Hua Kuang

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

The field of chiral inorganic nanostructures is rapidly expanding. It started from the observation of strong circular dichroism during the synthesis of individual nanoparticles (NPs) and their assemblies and expanded to sophisticated synthetic protocols involving nanostructures from metals, semiconductors, ceramics, and nanocarbons. Besides the well-established chirality transfer from bioorganic molecules, other methods to impart handedness to nanoscale matter specific to inorganic materials were discovered, including three-dimentional lithography, multiphoton chirality transfer, polarization effects in nanoscale assemblies, and others. Multiple chiral geometries were observed with characteristic scales from ångströms to microns. Uniquely high values of chiral anisotropy factors that spurred the development of the field and differentiate it from chiral structures studied before, are now well understood; they originate from strong resonances of incident electromagnetic waves with plasmonic and excitonic states typical for metals and semiconductors. At the same time, distinct similarities with chiral supramolecular and biological systems also emerged. They can be seen in the synthesis and separation methods, chemical properties of individual NPs, geometries of the nanoparticle assemblies, and interactions with biological membranes. Their analysis can help us understand in greater depth the role of chiral asymmetry in nature inclusive of both earth and space. Consideration of both differences and similarities between chiral inorganic, organic, and biological nanostructures will also accelerate the development of technologies based on chiroplasmonic and chiroexcitonic effects. This review will cover both experiment and theory of chiral nanostructures starting with the origin and multiple components of mirror asymmetry of individual NPs and their assemblies. We shall consider four different types of chirality in nanostructures and related physical, chemical, and biological effects. Synthetic methods for chiral inorganic nanostructures are systematized according to chirality types, materials, and scales. We also assess technological prospects of chiral inorganic materials with current front runners being biosensing, chiral catalysis, and chiral photonics. Prospective venues for future fundamental research are discussed in the conclusion of this review.

Nanoscale plasmonic assemblies display exceptionally strong chiral optical activity. So far, their structural design was primarily driven by challenges related to metamaterials whose practical applications are remote. Here we demonstrate that gold nanorods assembled by the polymerase chain reaction into DNA-bridged chiral systems have promising analytical applications. The chiroplasmonic activity of side-by-side assembled patterns is attributed to a 7-9 degree twist between the nanorod axes. This results in a strong polarization rotation that matches theoretical expectations. The amplitude of the bisignate 'wave' in the circular dichroism spectra of side-by-side assemblies demonstrates excellent linearity with the amount of target DNA. The limit of detection for DNA using side-by-side assemblies is as low as 3.7 aM. This chiroplasmonic method may be particularly useful for biological analytes larger than 2-5 nm which are difficult to detect by methods based on plasmon coupling and 'hot spots'. Circular polarization increases for inter-nanorod gaps between 2 and 20 nm when plasmonic coupling rapidly decreases. Reaching the attomolar limit of detection for simple and reliable bioanalysis of oligonucleotides may have a crucial role in DNA biomarker detection for early diagnostics of different diseases, forensics and environmental monitoring.

Chiral self-assembled nanomaterials with biological applications have attracted great interest. In this study, DNA-driven gold-upconversion nanoparticle (Au-UCNP) pyramids were fabricated to detect intracellular microRNA (miRNA) in real time. The Au-UCNP pyramids are doubly optically active, displaying strong plasmonic circular dichroism (CD) at 521 nm and significant luminescence in 500–600 nm, and therefore can be monitored by both of them. CD will decrease while the luminescence intensity increases in the presence of miRNA. The experimental results show that the CD intensity had an outstanding linear range from 0.073 to 43.65 fmol/10 μgRNA and a limit of detection (LOD) of 0.03 fmol/10 μgRNA, whereas the luminescence intensity ranged from 0.16 to 43.65 fmol/10 μgRNA with a LOD of 0.12 fmol/10 μgRNA. These data indicate that the CD signal is much more sensitive to the concentration of miRNA than the luminescent signal, which is attributed to the strong CD intensity arising from the spin angular momentum of the photon interaction with chiral nanostructures and the plasmonic enhancement of the intrinsic chirality of DNA molecules in the pyramids. This approach opens up a new avenue to the ultrasensitive detection and quantification of miRNA in living cells.

Chirality at the nanometer scale represents one of the most rapidly developing areas of research. Self-assembly of DNA–nanoparticle (NP) hybrids enables geometrically precise assembly of chiral isomers. The concept of a discrete chiral nanostructure of tetrahedral shape and topology fabricated from four different NPs located in the corners of the pyramid is fundamental to the field. While the first observations of optical activity of mixed pyramidal assemblies were made in 2009 (Chen, W.; Nano Lett. 2009, 9, 2153−2159), further studies are difficult without finely resolved optical data for precisely organized NP pyramidal enantiomers. Here we describe the preparation of a family of self-assembled chiral pyramids made from multiple metal and/or semiconductor NPs with a yield as high as 80%. Purposefully made R- and S-enantiomers of chiral pyramids with four different NPs from three different materials displayed strong chiroptical activity, with anisotropy g-factors as high as 1.9 × 10–2 in the visible spectral range. Importantly, all NP constituents contribute to the chiroptical activity of the R/S pyramids. We were able to observe three different circular dichroism signals in the range of 350–550 nm simultaneously. They correspond to the plasmonic oscillations of gold, silver, and bandgap transitions of quantum dots. Tunability of chiroptical bands related to these transitions is essential from fundamental and practical points of view. The predictability of optical properties of pyramids, the simplicity of their self-assembly in comparison with lithography, and the possibility for polymerase chain reaction-based automation of their synthesis are expected to facilitate their future applications.

Three disease biomarkers can simultaneously be detected at the attomolar level because of a novel surface-enhanced Raman scattering (SERS) encoded silver pyramid sensing system. This newly designed pyramidal sensor with well-controlled geometry exhibits highly sensitive, selective, and reproducible SERS signals, and holds promising potential for biodetection applications. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Chiral assemblies of nanoparticles (NPs) are typically constructed with helical or tetrahedral geometries. Simple pairs of NPs are not expected to display chirality due to basic symmetry considerations made under the assumption of their spherical geometry. In this study we demonstrate that assemblies consisting of two metallic NPs do possess chirality and strongly rotate polarization of light. Their chiroplasmonic properties are attributed to the prolate geometry of individual colloidal particles. When bridged by biomolecules, the NP pairs acquire scissor-like geometry, with the long axes of NPs forming an angle of ∼9°. This small dihedral angle results in chirality of the NP pair, while the consistency of its sign due to the specific conformation of the bridging biomacromolecules breaks the enantiomeric equivalence of the NP pairs. Strong polarization rotation in these nanoassemblies makes possible their utilization in biological analysis. Heterodimers of gold and silver NPs were made using antibody–antigen bridges. Taking advantage of their chiroplasmonic properties, we investigated their bioanalitical potential for detection of an environmental toxin, microcystin-LR, and a cancer biomarker, prostate-specific antigen. The order-of-magnitude improvements in limits of detection compared to all other analytical techniques are attributed to plasmonic enhancement of intrinsic chirality of biological compounds, strong optical coupling of photons with NP assemblies with twisted geometries, and signal amplification due to the bisignate nature of circular dichroism bands.

Multiple properties of plasmonic assemblies are determined by their geometrical organization. While high degree of complexity was achieved for plasmonic superstructures based on nanoparticles (NPs), little is known about the stable and structurally reproducible plasmonic assemblies made up from geometrically diverse plasmonic building blocks. Among other possibilities, they open the door for the preparation of regiospecific isomers of nanoscale assemblies significant both from a fundamental point of view and optical applications. Here, we present a synthetic method for complex assemblies from NPs and nanorods (NRs) based on selective modification of NRs with DNA oligomers. Three types of assemblies denoted as End, Side, and Satellite isomers that display distinct elements of regiospecificity were prepared with the yield exceeding 85%. Multiple experimental methods independently verify various structural features, uniformity, and stability of the prepared assemblies. The presence of interparticle gaps with finely controlled geometrical parameters and inherently small size comparable with those of cellular organelles fomented their study as intracellular probes. Against initial expectations, SERS intensity for End, Side, and Satellite isomers was found to be dependent primarily on the number of the NPs in the superstructures rationalized with the help of electrical field simulations. Incubation of the label-free NP-NR assemblies with HeLa cells indicated sufficient field enhancement to detect structural lipids of mitochondria and potentially small metabolites. This provided the first proof-of-concept data for the possibility of real-time probing of the local organelle environment in live cells. Further studies should include structural optimization of the assemblies for multitarget monitoring of metabolic activity and further increase in complexity for applications in transformative optics.

The development of a unique and universal strategy for the simultaneous quantification of different types of biomolecules (i.e., nucleic acids and proteins) in living cells is extremely challenging. Herein, a two-signal platform, based upon surface-enhanced Raman scattering and upconversion, for the ultrasensitive and quantitative in situ detection of microRNA (miR)-21 and telomerase in living cells is reported. In the presence of miR-21 and telomerase, the hybridization of miR-21 with a molecular beacon leads to the separation of 3,3′-diethylthiocarbamyl cyanine iodide-modified Au NR dimers, resulting in a decrease in Raman signal. Also, the target telomerase triggers elongation of the telomerase primer strands, followed by substitutional hybridization and release of upconversion nanoparticles, leading to an increase in luminescence. A linear relationship between the Raman intensities and logarithmic concentration of intracellular miR-21 between 0.021 and 22.36 amol/ngRNA is observed, and the limit of detection (LOD) was determined to be 0.011 amol/ngRNA. The luminescence data show a linear response between 0.6 × 10–12 and 31 × 10–12 IU for logarithmic concentration of intracellular telomerase with a LOD of 3.2 × 10–13 IU. These results are in good agreement with Raman and confocal imaging. Importantly, the ultrasensitive detection of miR-21 was possible due to strong plasmonic “hot spots”. This innovative two-signal approach can be utilized for the quantitative and precise detection of many types of signaling molecules in living cells and to understand the chemistry within cellular systems and its application in the diagnosis of disease.

Parallel or angle parked: Gold nanorods (see picture) were selectively modified either on the sides or ends using complementary microcystin (MC-LR) antibody and antigen (blue). Fast detection of MC-LR (green) was successfully achieved with these assemblies, and both sensitivity and detection ranges were markedly better for the end-to-end motif (right) than the side-to-side variant (left). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

DNA-driven hierarchical core–satellite nanostructures with plasmonic gold nanorod dimers and upconversion nanoparticles are fabricated. Once the core–satellite structure is activated, combined photothermal therapy and photodynamic therapy are carried out under the guidance of upconversion luminesce, T1-weighted magnetic resonance, photoacoustics, and computed tomography imaging of tumors in vivo, which exhibit the multifunctional biological applications of the DNA-based self-assemblies. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Integration of nanoparticles (NPs) and other nanomaterials with existing technologies must take place in order to substantially widen the spectrum of their applications. This task can be simplified by taking advantage of NP assemblies provided that they retain the unique properties of nanomaterials in organized systems of larger dimensions. There is a large variety of methods of assembling NPs into superstructures containing 10-10(10) particles that include field-, bio-, and interface-directed techniques as well as self-organization. Some of them can traverse the scales from typical lengths of 10(-9) m (nano) to 10(-5) m (micro) and 10(1) m (macro) conducive to other technologies. Such dimensional transformation of nanomaterials makes possible utilization of well-established processing techniques, and hardware tools operating at these scales. Therefore, answering the question "What types of the assembly techniques are suitable for such a task?" is vital for the future application of nanoscale materials in any field of use. These techniques must result in organized structures of at least 5 × 10(-7) m in size, offer relative simplicity and fault tolerance. This review focuses on the recent development of NP assembly techniques that have the possibility of satisfying these requirements. The expected applications and future developments are also discussed.

Although nanoparticle (NP) assemblies are at the beginning of their development, their unique geometrical shapes and media-responsive optical, electronic, and magnetic properties have attracted significant interest. Nanoscale assembly bridges multiple levels of hierarchy of materials: individual nanoparticles, discrete molecule-like or virus-like nanoscale agglomerates, microscale devices, and macroscale materials. The capacity to self-assemble can greatly facilitate the integration of nanotechnology with other technologies and, in particular, with microscale fabrication. In this Account, we describe developments in the emerging field of dynamic NP assemblies, which are spontaneously form superstructures containing more than two inorganic nanoscale particles that display the ability to change their geometrical, physical, chemical, and other attributes. In many ways, dynamic assemblies can represent a bottleneck in the "bottom-up" fabrication of NP-based devices because they can produce a much greater variety of assemblies, but they also provide a convenient tool for variation of geometries and dimensions of nanoparticle assemblies. Superstructures of NPs (and those held together by similar intrinsic forces)are classified into two groups: Class 1 where media and external fields can alter shape, conformation, and order of stable super structures with a nearly constant number of NPs or Class 2 where the total number of NPs changes, while the organizational motif in the final superstructure remains the same. The future development of successful dynamic assemblies requires understanding the equilibrium in dynamic NP systems. The dynamic nature of Class 1 assemblies is associated with the equilibrium between different conformations of a superstructure and is comparable to the isomerization in classical chemistry. Class 2 assemblies involve the formation or breakage of linkages between the NPs, which is analogous to the classical chemical equilibrium for the formation of a molecule from atoms. Finer classification of NP assemblies in accord with established conventions in the field may include different size dimensionalities: discrete assemblies (artificial molecules) and one-dimensional (spaced chains), two-dimensional (sheets), and three-dimensional (superlattices, twisted structures) assemblies. Notably, these dimensional attributes must be regarded as primarily topological in nature because all of these superstructures can acquire complex three-dimensional shapes. We discuss three primary strategies used to prepare NP superstructures: (1) anisotropy-based assemblies utilizing either intrinsic force field anisotropy around NPs or external anisotropy associated with templates or applied fields, (2) assembly methods utilizing uniform NPs with isotropic interactions, and (3) methods based on mutual recognition of biomolecules, such as DNA and antigen-antibody interactions. We consider optical, electronic, and magnetic properties of dynamic superstructures, focusing primarily on multiparticle effects in NP superstructures as represented by surface plasmon resonance, NP-NP charge transport, and multibody magnetization. Unique properties of NP superstructures are being applied to biosensing, drug delivery, and nanoelectronics. For both Class 1 and Class 2 dynamic assemblies, biosensing is the most dominant and well-developed area of dynamic nanostructures being successfully transitioned into practice. We can foresee the rapid development of dynamic NP assemblies toward applications in harvesting of dissipated energy, photonics, and electronics. The final part of this Account is devoted to the fundamental questions facing dynamic assemblies of NPs in the future.

A self-assembled nanostar dimer based on the Hg(2+)-mediated T-T base pair of ssDNA has been developed as a SERS sensor for Hg(2+) detection. The enormous enhancement of the electromagnetic field by the dimer structures facilitates extraordinary SERS intensity. The LOD is 0.8 pg mL(-1) and its linear range is 0.002 to 1 ng mL(-1).

Chiral nanoscale photonic systems typically follow either tetrahedral or helical geometries that require four or more different constituent nanoparticles. Smaller number of particles and different chiral geometries taking advantage of the self-organization capabilities of nanomaterials will advance understanding of chiral plasmonic effects, facilitate development of their theory, and stimulate practical applications of chiroplasmonics. Here we show that gold nanorods self-assemble into side-by-side orientated pairs and "ladders" in which chiral properties originate from the small dihedral angle between them. Spontaneous twisting of one nanorod versus the other one breaks the centrosymmetric nature of the parallel assemblies. Two possible enantiomeric conformations with positive and negative dihedral angles were obtained with different assembly triggers. The chiral nature of the angled nanorod pairs was confirmed by 4π full space simulations and the first example of single-particle CD spectroscopy. Self-assembled nanorod pairs and "ladders" enable the development of chiral metamaterials, (bio)sensors, and new catalytic processes.

Dopamine (DA) is a neurotransmitter which plays a key role in the life science. Self-assembled Au@Ag nanorod dimers based on aptamers were developed for ultrasensitive dopamine detection. The electronic field was significantly enhanced by the addition of silver shell coating on the surface of Au NR dimer. The results displayed that Au@Ag NR dimers were ideal building blocks for constructing the SERS substrates with prominent Raman enhancement effects. It was found that with using this Surface-enhanced Raman scattering (SERS)-encoded this sensing system, a limit of detection of 0.006 pM and a wide linear range of 0.01-10 pM for dopamine detection were obtained. Our work open up a new avenue for the diagnosis and drug-discovery programs.

DNA-bridged pairs of seemingly spherical metallic nanoparticles (NPs) have chiral geometry due to the nonideal oblong shape of the particles and scissor-like conformation. Here we demonstrate that deposition of gold and silver shells around the NP heterodimers enables spectral modulation of their chiroplasmonic bands in 400–600 nm region and results in significantly enhanced optical activity with g-factors reaching 1.21 × 10–2. The multimetal heterodimers optimized for coupling with the spin angular momentum of incident photons enable polymerase chain reaction (PCR)-based DNA detection at the zeptomolar level. This significant improvement in the sensitivity of detection is attributed to improvement of base pairing in the presence of NPs, low background for chiroplasmonic detection protocol, and enhancement of photon–plasmon coupling for light with helicity matching that of the twisted geometry of the heterodimers.

A semi-quantitative and quantitative multi-immunochromatographic (ICA) strip detection assay was developed for the simultaneous detection of twenty types of mycotoxins from five classes, including zearalenones (ZEAs), deoxynivalenols (DONs), T-2 toxins (T-2s), aflatoxins (AFs), and fumonisins (FBs), in cereal food samples. Sensitive and specific monoclonal antibodies were selected for this assay. The semi-quantitative results were obtained within 20 min by the naked eye, with visual limits of detection for ZEAs, DONs, T-2s, AFs and FBs of 0.1-0.5, 2.5-250, 0.5-1, 0.25-1 and 2.5-10 μg kg(-1), and cut-off values of 0.25-1, 5-500, 1-10, 0.5-2.5 and 5-25 μg kg(-1), respectively. The quantitative results were obtained using a hand-held strip scan reader, with the calculated limits of detection for ZEAs, DONs, T-2s, AFs and FBs of 0.04-0.17, 0.06-49, 0.15-0.22, 0.056-0.49 and 0.53-1.05 μg kg(-1), respectively. The analytical results of spiked samples were in accordance with the accurate content in the simultaneous detection analysis. This newly developed ICA strip assay is suitable for the on-site detection and rapid initial screening of mycotoxins in cereal samples, facilitating both semi-quantitative and quantitative determination.

MicroRNAs (miRNAs), a kind of single-stranded small RNA molecules, play a crucial role in physiological and pathological processes in human beings. We describe here the detection of miRNA, by side-by-side self-assembly of plasmonic nanorod dimers in living cells, which gives rise to a distinct intense chiroplasmonic response and surface-enhanced Raman scattering (SERS). The dynamic assembly of chiral nanorods was confirmed by fluorescence resonance energy transfer (FRET), also in living cells. Our study provides insights into in situ self-assembly of plasmonic probes for the real-time measurement of biomarkers in living cells. This could improve the current understanding of cellular RNA-protein complexes, pharmaco-genomics, and genetic diagnosis and therapies.

Optoelectronic effects differentiating absorption of right and left circularly polarized photons in thin films of chiral materials are typically prohibitively small for their direct photocurrent observation. Chiral metasurfaces increase the electronic sensitivity to circular polarization, but their out-of-plane architecture entails manufacturing and performance trade-offs. Here, we show that nanoporous thin films of chiral nanoparticles enable high sensitivity to circular polarization due to light-induced polarization-dependent ion accumulation at nanoparticle interfaces. Self-assembled multilayers of gold nanoparticles modified with L-phenylalanine generate a photocurrent under right-handed circularly polarized light as high as 2.41 times higher than under left-handed circularly polarized light. The strong plasmonic coupling between the multiple nanoparticles producing planar chiroplasmonic modes facilitates the ejection of electrons, whose entrapment at the membrane-electrolyte interface is promoted by a thick layer of enantiopure phenylalanine. Demonstrated detection of light ellipticity with equal sensitivity at all incident angles mimics phenomenological aspects of polarization vision in marine animals. The simplicity of self-assembly and sensitivity of polarization detection found in optoionic membranes opens the door to a family of miniaturized fluidic devices for chiral photonics.

For decades, chiral nanomaterials have been extensively studied because of their extraordinary properties. Chiral nanostructures have attracted a lot of interest because of their potential applications including biosensing, asymmetric catalysis, optical devices, and negative index materials. Circularly polarized light (CPL) is the most attractive source for chirality owing to its high availability, and now it has been used as a chiral source for the preparation of chiral matter. In this review, the recent progress in the field of CPL-enabled chiral nanomaterials is summarized. Firstly, the recent advancements in the fabrication of chiral materials using circularly polarized light are described, focusing on the unique strategies. Secondly, an overview of the potential applications of chiral nanomaterials driven by CPL is provided, with a particular emphasis on biosensing, catalysis, and phototherapy. Finally, a perspective on the challenges in the field of CPL-enabled chiral nanomaterials is given.

Flupyradifurone (FPF) is a neonicotinoid insecticide that effectively controls the spread of various pests. In this study, we established an immunochromatographic assay based on a highly specific and sensitive anti-FPF monoclonal antibody (mAb) to screen for FPF residues in grapes, blueberries, and tomatoes. The cut-off value for the immunochromatographic assay was 5 mg/kg for grapes and 10 mg/kg for blueberries and tomatoes. The calculated limit of detection of the immunochromatographic assay was 0.009 mg/kg, 0.033 mg/kg, and 0.040 mg/kg for grapes, blueberries, and tomatoes, respectively. The recovery rates of the immunochromatographic assay were 97.0-108.2 % in grape samples, 90.9-105.1 % in blueberry samples, and 94.0-103.7 % in tomato samples, and the detection results were highly consistent with LC-MS/MS results. Therefore, this immunochromatographic assay was an effective and rapid tool for screening for FPF in grapes, blueberries, and tomatoes.

An ultrasensitive and rapid electrochemical platform for the specific detection of ochratoxin A (OTA) was developed. In this method, three single-stranded DNA molecules, including the aptamer, were immobilized on the surface of an electrode. Binding of the OTA target analyte to the aptamer changed the redox current of methylene blue (MB), which was used as the electrochemical probe, in a manner that was dependent on OTA concentration. With signal enhancement from gold nanoparticle-functionalized DNA, the sensitivity of this method for OTA was as low as 30 pg/mL, and the effective sensing range was from 0.1 to 20 ng/mL. To investigate the sensing process, the conformational switch of the aptamer was studied by circular dichroism (CD), which confirmed the recognition of the aptamer by the target OTA. Given its sensitivity and rapid detection, we believe this approach has the potential to be a main technology for the detection of toxins in the field of food safety, and in other areas.

Melamine (MEL) is an emerging contaminant in milk, infant formula and pet food, and is the subject of much recent research. This review focuses on analytical methods for detecting MEL residue. We present and discuss the advantages, the disadvantages and the applicability of methods, including common techniques [e.g., capillary electrophoresis, high-performance liquid chromatography (HPLC), LC with mass spectrometry (LC-MS), LC with tandem (LC-MS2), gas chromatography with MS (GC-MS), matrix-assisted laser desorption/ionization MS (MALDI-MS), nuclear magnetic resonance spectroscopy, vibrational spectroscopy, chemiluminescence analysis and immunoassay] and several novel detection methods. We propose that the new generation of analytical methods for detecting MEL requires development of powerful analytical devices, combination of multiple techniques, and application of new materials.

Here, we report a simple fluorescent strip sensor based on aptamer-quantum dots technology that can meet toxin monitoring demands using ochratoxin A (OTA) as a model toxin. The limit of the detection (LOD) for the fluorescent strip was 1.9 ng mL(-1), while the time needed for the detection is only 10 min; this conforms to the standards of World Health Organization (WHO) or better. Overall functional parameters are also better than the analogous characteristics of gold nanoparticle strips. High selectivity was maintained as well, making them suitable for the samples with complex solution composition.

An aptamer-based chromatographic strip assay method for rapid toxin detection was developed. The aptamer-based strip assay was based on the competition for the aptamer between ochratoxin A and DNA probes. The sensing results indicated that the sensitivity of the aptamer-based strip was better than that of conventional antibody-based strips. The visual limit of detection of the strip for qualitative detection was 1 ng/mL while the LOD for semi-quantitative detection could down to 0.18 ng/mL by using scanning reader. The recoveries of test samples were from 96% to 110%. All detections could be achieved in less than 10 min, indicating that the aptamer-based strip could be a potential useful tool for rapid on-site detections.

A surface-enhanced Raman scattering (SERS) sensor based on gold nanostar (Au NS) core-silver nanoparticle (Ag NP) satellites was fabricated for the first time to detect aflatoxinB1 (AFB1). We constructed the SERS sensor using AFB1 aptamer (DNA1)-modified Ag satellites and a complementary sequence (DNA2)-modified Au NS core. The Raman label (ATP) was modified on the surface of Ag satellites. The SERS signal was enhanced when the satellite NP was attached to the Au core NS. The AFB1 aptamer on the surface of Ag satellites would bind to the targets when AFB1 was present in the system, Ag satellites were then removed and the SERS signal decreased. This SERS sensor showed superior specificity for AFB1 and the linear detection range was from 1 to 1000 pg mL(-1) with the limit of detection (LOD) of 0.48 pg mL(-1). The excellent recovery experiment using peanut milk demonstrated that the sensor could be applied in food and environmental detection.

Advanced MaterialsVolume 28, Issue 28 p. 5907-5915 Communication Propeller-Like Nanorod-Upconversion Nanoparticle Assemblies with Intense Chiroptical Activity and Luminescence Enhancement in Aqueous Phase Xiaoling Wu, Xiaoling Wu State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this authorLiguang Xu, Liguang Xu State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this authorWei Ma, Wei Ma State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this authorLiqiang Liu, Liqiang Liu State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this authorHua Kuang, Corresponding Author Hua Kuang State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaE-mail: kuangh@jiangnan.edu.cnSearch for more papers by this authorNicholas A. Kotov, Nicholas A. Kotov Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, 48109-2136 USASearch for more papers by this authorChuanlai Xu, Chuanlai Xu State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this author Xiaoling Wu, Xiaoling Wu State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this authorLiguang Xu, Liguang Xu State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this authorWei Ma, Wei Ma State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this authorLiqiang Liu, Liqiang Liu State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this authorHua Kuang, Corresponding Author Hua Kuang State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaE-mail: kuangh@jiangnan.edu.cnSearch for more papers by this authorNicholas A. Kotov, Nicholas A. Kotov Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, 48109-2136 USASearch for more papers by this authorChuanlai Xu, Chuanlai Xu State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. China International Joint Research Laboratory for Biointerface and Biodetection and School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122 P. R. ChinaSearch for more papers by this author First published: 09 May 2016 https://doi.org/10.1002/adma.201601261Citations: 118Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Propeller-like nanoscale assemblies with exceptionally intense chiroptical activity and strong luminescence are prepared using gold nanorods and upconversion nanoparticles. The circular dichroism intensity of the tetramer reached 80.9 mdeg, with g-factor value of 2.1 × 10–2. The enhancement factor of upconversion luminescence is as high as 21.3 in aqueous phase. Attomolar bioanalysis of a cancer biomarker with two model is also achieved, showing potential for early disease diagnosis and environmental monitoring. Citing Literature Supporting Information As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Filename Description adma201601261-sup-0001-S1.pdf889.9 KB Supplementary Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. Volume28, Issue28July 27, 2016Pages 5907-5915 RelatedInformation

In this study, we have first developed a rapid and sensitive strip immunosensor based on two heterogeneously-sized gold nanoparticles (Au NPs) probes for the detection of trace lead ions in drinking water. The sensitivity was 4-fold higher than that of the conventional LFA under the optimized conditions. The visual limit of detection (LOD) of the amplified method for qualitative detection lead ions was 2 ng/mL and the LOD for semi-quantitative detection could go down to 0.19 ng/mL using a scanning reader. The method suffered from no interference from other metal ions and could be used to detect trace lead ions in drinking water without sample enrichment. The recovery of the test samples ranged from 96% to 103%. As the detection method could be accomplished within 15 min, this method could be used as a potential tool for preliminary monitoring of lead contamination in drinking water.

In this paper, we describe the development of a multicomponent lateral-flow assay based on an antibody–antigen reaction for the rapid and simultaneous detection of trace contaminants in water, including a heavy metal, algal toxin, antibiotic, hormone, and pesticide. The representative analytes chosen for the study were lead (Pb(II), microcystin–leucine–arginine (MC–LR), chloramphenicol (CAP), testosterone (T), and chlorothalonil (CTN). Five different antigens were immobilized separately in five test lines on a nitrocellulose membrane. The monoclonal antibodies specifically recognized the corresponding antigens, and there was no cross-reactivity between the antibodies in the detection assay. Samples or standards containing the five analytes were preincubated with the freeze-dried colloidal-gold-labeled monoclonal antibody conjugates to improve the sensitivity of the assay. The results were obtained within 20 min with a paper-based sensor. The cut-off values for the strip test were 4 ng/mL for Pb(II), 1 ng/mL for MC–LR, 0.1 ng/mL for CAP, 5 ng/mL for T, and 5 ng/mL for CTN. The assay was evaluated using spiked water samples, and the accuracy and reproducibility of the results were good. In summary, this lateral-flow device provides an effective and rapid method for the onsite detection of multiple contaminants in water samples, with no treatment or devices required.

Melamine toxicity causing the renal failure and death of animals and humans has recently attracted worldwide attention. Developing an easy, fast, and sensitive method for the routine melamine detection is of great importance. Herein, we report the colorimetric sensing of melamine, based on the 18-crown-6 ether functionalized gold nanoparticles (GNPs) through the formation of cavity complexes with amines. Based on high extinction coefficients and spectral sensitivity of the surface plasmon resonance band of the GNPs, the rapid and sensitive melamine detection was achieved both visually and spectroscopically. Under the optimal conditions, melamine could be selectively detected in a concentration range from 10 to 500 ppb with a limit of detection as 6 ppb (3σ), which is much lower than the strictest melamine safety requirement of 1 ppm. To demonstrate the selectivity and practicality of the method, melamine detection was realized in the real complex samples (dairy) with excellent analyte concentration recovery, indicating its applicability for real-time monitoring of toxins in common products. Crown ether assembly of GNP also opens a new route for the formation of three-dimensional pseudorotaxane-like assemblies of nanoparticles that can be applicable to a variety of amine-bearing ligands.

Abstract Assemblies of nanomaterials for biological applications in living cells have attracted much attention. Herein, graphene oxide (GO)–gold nanoparticle (Au NP) assemblies are driven by a splint DNA strand, which is designed with two regions at both ends that are complementary with the DNA sequence anchored on the surface of the GO and the Au NPs. In the presence of microRNA (miR)‐21 and epithelial cell‐adhesion molecule (EpCAM), the hybridization of miR‐21 with a molecular probe leads to the separation of 6‐fluorescein‐phosphoramidite‐modified Au NPs from GO, resulting in a decrease in the Raman signal, while EpCAM recognition reduces circular dichroism (CD) signals. The CD signals reverse from negative in original assemblies into positive when reacted with cells, which correlates with two enantiomer geometries. The EpCAM detection has a good linear range of 8.47–74.78 pg mL −1 and a limit of detection (LOD) of 3.63 pg mL −1 , whereas miR‐21 detection displays an outstanding linear range of 0.07–13.68 amol ng −1 RNA and LOD of 0.03 amol ng −1 RNA . All the results are in good agreement with those of the Raman and confocal bioimaging. The strategy opens up an avenue to allow the highly accurate and reliable diagnosis (dual targets) of clinic diseases.

Gold‐gap‐silver nanostructures (GGS NSs) with interior nanobridged gaps are enantioselectively fabricated. Guided by l/d ‐cysteine, the GGS‐L/D (L/D represents l/d ‐cysteine) NSs show reversed plasmon‐induced circular dichroism (CD) signals in the visible region. It is found that the nanogap plays a key role in the plasmonic CD of GGS NSs and the chiroptical response can be tailored by adjusting the amount of cysteine. The anisotropy factor of GGS‐L/D NSs with a 0.5 nm interior gap at 430 nm is as high as ≈0.01. The circularly polarized photocatalytic activity of GGS NSs is examined. It is shown that upon irradiation with left‐circularly polarized light, the catalytic efficiency of GGS‐L NSs is 73‐fold and 17‐fold higher than that of Au nanoparticles (NPs) and Au@Ag core–shell NPs, respectively. Upon irradiation with right‐circularly polarized light, the catalytic activity of GGS‐D NSs is about 71 times and 17 times higher than that of Au NPs and Au@Ag core–shell NPs, respectively. These unique chiral NSs with high plasmonic response can be applied to enantioselective catalysis.

Assemblies of plasmonic nanoparticles enable new modalities for biosensing. Engineered superstructures from metal nanoparticles can enhance the plasmon resonances and chiroptical activity of nanoscale dispersions. Such phenomena are keys to the fabrication of highly sensitive, selective and fast-responding detection platforms, making them promising candidates for clinical applications. This tutorial review summarizes and discusses recent advances in this area. The topics covered in the review include the basic strategies adopted for assembly and engineering of plasmonic nanoparticles, optical properties of the assembled nanostructures and their applications to both in vitro and in vivo detection of biological compounds. We also offer our vision of the future prospects of this field of research. Among emerging applications in this area are novel nanosensors and platforms, for food safety, environmental monitoring, health safeguarding, as well as biodefense.

The highly sensitive and quantitative biodetection of intracellular telomerase is challenging. A DNA‐driven nanoparticle self‐assembling pyramid encoding a Raman reporter (Cy5) is reported that detects telomerase in live cells. In the presence of the target, the telomerase primer is extended and the inner DNA chain is replaced, leading to the reduction in the surface‐enhanced Raman scattering (SERS) signal and the simultaneous recovery of the fluorescent signal. The SERS signal has a linear range for the detection of telomerase in situ of 1 × 10 –14 to 5 × 10 –11 IU, with a limit of detection of 6.2 × 10 –15 IU. The fluorescent signal is used to confirm the intracellular telomerase activity, demonstrating the efficacy of the designed pyramid probe. This biosensing strategy provides a reliable and ultrasensitive protocol for the quantification of biomarkers in living cells.

This review discusses the application of quantum dots (QDs) to chemical and biological detection, for which they have excellent features, particularly size-dependent optical properties. We can summarize the main areas discussed in this review as follows: (1) QDs associated with enzyme-linked immunosorbent assay (ELISA), chip detection and capillary electrophoresis (CE) enhance the sensitivity and the speed of detection of residues; (2) QDs are applied with other techniques, including polymerase chain reaction (PCR), fluorescence resonance-energy transfer (FRET) analysis, fluorescence in-situ hybridization (FISH) and western blot analysis; and, (3) QDs combined with the above techniques can successfully detect DNA and protein. We also cover perspectives and challenges in analytical applications of QDs.

This study strategically fabricates multifunctional nanopyramids to allow the ultrasensitive quantification of dual microRNAs (miR-203b and miR-21) in living cells and their responsive bioimaging in vivo. The nanopyramids, composed of Au-Cu9 S5 nanoparticles (NPs), upconversion NPs (UCNPs), and Ag2 S NPs, emit two luminescent signals simultaneously with excitation at 808 nm, arising from the UCNPs at 541 nm in the visible region and from the Ag2 S NPs at 1227 nm in the second window of near-infrared (NIR-II) region. The upconversion luminescence has a linear relationship with miR-203b from 0.13 to 54.54 fmol per 10 µgRNA and a limit of detection (LOD) of 0.09 fmol per 10 µgRNA , whereas the Ag2 S NP luminescence has a linear relationship with miR-21 from 0.37 to 43.56 fmol per 10 µgRNA , with a LOD of 0.23 fmol per 10 µgRNA . Significantly, this study demonstrates that the nanopyramids can be successfully used for miRs-responsive bioimaging in a tumor-bearing animal model. Furthermore, taking advantage of the photothermal capabilities of pyramids, the tumors can also be eliminated completely. These nanopyramids not only overcome the obstacles in the simultaneous detection of multiple miRs at the cellular level but also provide a cancer theranostic platform in vivo.

Mercuric ions (Hg2+) mediate the transformation of single-stranded DNA to form double helical DNA by T–Hg2+–T interaction between base pairs. With this strategy, DNA modified gold nanoparticles (Au NPs) were assembled into chains which were displayed remarkable surface-enhanced Raman scattering (SERS) signal. Under optimized conditions, the length of gold nanochains was directly proportional to the mercuric ions concentrations over 0.001–0.5 ng mL−1 and the limit of detection (LOD) in drinking water was as low as 0.45 pg mL−1. With ultrasensitivity and excellent selectivity, this feasible and simple method is potentially as a promising tool for monitoring of mercury ions in food safety and environmental applications.

Abstract The development of artificial chiral architectures, especially chiral inorganic nanostructures, has greatly promoted research into chirality in nanoscience. The nanoscale chirality of artificial chiral nanostructures offers many new application opportunities, including chiral catalysis, asymmetric synthesis, chiral biosensing, and others that may not be allowed by natural chiral molecules. Herein, the progress achieved during the past decade in chirality‐associated biological applications (biosensing, biolabeling, and bioimaging) combined with individual chiral nanostructures (such as chiral semiconductor nanoparticles and chiral metal nanoparticles) or chiral assemblies is discussed.

Group-specific monoclonal antibodies (Mabs) with selectivity for 27 sulfonamides were developed based on new combinations of immunogen and coating antigen. The Mab was able to recognize 27 sulfonamides with 50% inhibition concentration (IC50) values ranging from 0.15 to 15.38 μg/L. In particular, the IC50 values for five sulfonamides (sulfamethazine, sulfaquinoxaline, sulfamonomethoxine, sulfadimethoxine, and sulfamethoxazole) were 0.51, 0.15, 0.56, 0.54, and 2.14 μg/L, respectively. On the basis of the Mab, an immunochromatographic lateral flow strip test was established for rapid screening of sulfonamides in honey samples. The visual limit of detection of the strip test for most sulfonamides in spiked honey samples was below 10 μg/kg, satisfying the requirements of authorities. Positive honey and pork liver samples, which had been confirmed by high-performance liquid chromatography/mass spectrometry, were used to validate the reliability of the proposed strip test. The immunochromatographic lateral flow strip test provides a rapid and convenient method for fast screening of sulfonamides in honey samples.

Photodynamic therapy (PDT) agent, which generates singlet oxygen ( 1 O 2 ) under light, has attracted significant attention for its broad biological and medical applications. Here, DNA‐driven shell–satellite (SS) gold assemblies as chiral photosensitizers are first fabricated. The chiral plasmonic nanostructure, coupling with cysteine enantiomers on its surface, exhibits intense chiroplasmonic activities (−40.2 ± 2.6 mdeg) in the visible region. These chiral SS nanoassemblies have high reactive oxygen species generating efficiency under circular polarized light illumination, resulting in a 1 O 2 quantum yield of 1.09. Meanwhile, it is found that SS could be utilized as PDT agent with remarkable efficiency under right circular polarized light irradiation in vitro and in vivo, allowing X‐ray computed tomography (CT) and photoacoustics (PA) imaging for tumors simultaneously. The achievements reveal that the enantiomer‐dependent and structure‐induced nanoassemblies play an important role in PDT effects. The present researches open up a new avenue for cancer diagnose and therapy using chiral nanostructures as multifunctional platform.

An ultrasensitive method for surface enhanced Raman scattering (SERS) detection of prostate-specific antigens (PSAs) was established based on the aptamer directed core-satellite nanostructures. A limit of detection (LOD) of 4.8 aM for PSA was obtained.

Here, a triple Raman label-encoded gold nanoparticle (AuNP) trimer is fabricated for heavy metal ion detection. In the presence of target ions, the gold nanoparticles modified with different Raman labels are assembled into trimers and produce different enhancements of Raman reporters, which are functionalized as Raman probes for simultaneous silver and mercury ion detection. Under optimized conditions, the limits of detection of Ag+ and Hg2+ reach 8.42 × 10–12 and 16.78 × 10–12m, respectively. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

A novel, rapid and ultrasensitive surface-enhanced Raman scattering (SERS) immunoassay for the detection of microcystin LR was developed based on the assembly of gold nanorods (GNRs). GNRs were assembled into nanorod chains through the bio-recognition. The SERS signal of the probe molecule modified to the end of the NRs could be enhanced due to the hot spot between the NRs. Meanwhile, the finite integration technique simulation revealed that the electrical field of nanorods was increased obviously depending on the degree of end to end assembled structures. The research results demonstrated that the linear detection range was from 0.01 ng mL−1 to 5 ng mL−1, the limit of detection was 5 pg mL−1, and the time necessary for the analysis was only 15 min.

Nucleic acids are natural biopolymers of nucleotides that store, encode, transmit and express genetic information, which play central roles in diverse cellular events and diseases in living things. The analysis of nucleic acids and nucleic acids-based analysis have been widely applied in biological studies, clinical diagnosis, environmental analysis, food safety and forensic analysis. During the past decades, the field of nucleic acids analysis has been rapidly advancing with many technological breakthroughs. In this review, we focus on the methods developed for analyzing nucleic acids, nucleic acids-based analysis, device for nucleic acids analysis, and applications of nucleic acids analysis. The representative strategies for the development of new nucleic acids analysis in this field are summarized, and key advantages and possible limitations are discussed. Finally, a brief perspective on existing challenges and further research development is provided.

The intra- and extracellular positioning of plasmonic nanoparticles (NPs) can dramatically alter their curative/diagnostic abilities and medical outcomes. However, the inability of common spectroscopic identifiers to register the events of transmembrane transport denies their intracellular vs. extracellular localization even for cell cultures. Here we show that the chiroptical activity of DNA-bridged NP dimers allows one to follow the process of internalization of the particles by the mammalian cells and to distinguish their extra- vs intra-cellular localizations by real-time spectroscopy in ensemble. Circular dichroism peaks in the visible range change from negative to positive during transmembrane transport. The chirality reversal is associated with a spontaneous twisting motion around the DNA bridge caused by the large change in electrostatic repulsion between NPs when the dimers move from interstitial fluid to cytosol. This finding opens the door for spectroscopic targeting of plasmonic nanodrugs and quantitative assessment of nanoscale interactions. The efficacy of dichroic targeting of chiral nanostructures for biomedical applications is exemplified here as photodynamic therapy of malignancies. The efficacy of cervical cancer cell elimination was drastically increased when circular polarization of incident photons matched to the preferential absorption of dimers localized inside the cancer cells, which is associated with the increased generation of reactive oxygen species and their preferential intracellular localization.

In this study, we established gold nanorods (Au NRs) core-silver nanoparticles (Ag NPs) satellite assemblies as an ultrasensitive aptamer-based SERS sensor for the detection of Mucin-1, a specific breast cancer marker protein. The limit of detection (LOD) was 4.3 aM and the wide linear range was 0.005-1 fM.

A high yield DNA-driven gold-quantum dot core-satellite is developed for miRNA detection in vitro and vivo. In the presence of the target miRNA, the DNA hairpin between core and satellite is ruined, resulting in the recovery of fluorescence. The limit of detection for miRNA-21 detection in living cells reaches 296 copies per cell.

Accurate and highly sensitive detection of Pantoea stewartii sbusp. stewartii-NCPPB 449 (PSS) is urgently required for international shipments due to tremendous agricultural economic losses. Herein, a dual amplified electrochemical sandwich immunosensor for PSS detection was developed, utilizing the good specificity and low cost of electrochemical immunoassay, the favorable conductivity and large specific surface area of gold nanoparticles (Au NPs), and the excellent catalytic ability of and horseradish peroxidase (HRP). A linear curve between current response and PSS concentration was established, and the limit of detection (LOD) was 7.8 × 103 cfu/mL, which is 20 times lower than that for conventional enzyme-linked immunosorbent assay (ELISA). This strategy is a useful approach for the highly sensitive detection of plant pathogenic bacterium.

Abstract Here, we construct a handedness‐dependent circular polarized light (CPL)‐activated chiral satellite assemblies formed from DNAzymes and spiny platinum modified with gold nanorods and upconversion nanoparticles (UCNPs), enabling the simultaneous quantitative analysis of multiple divalent metal ions in living cells. The chiral nanoprobes, in coordination with their corresponding divalent metal ions under 980 nm left circular polarized (LCP) light illumination, served as an in situ confocal bioimaging platform for the quantitation of the given intracellular metal ions. The limit of detection (LOD) of the chiral probes in living cells is 1.1 nmol/10 6 cells, 1.02 nmol/10 6 cells and 0.45 nmol/10 6 cells for Zn 2+ , Mg 2+ , and Cu 2+ , respectively.

Abstract In this study, via a simple one‐step method, chiral copper sulfide quantum dots (d/l‐QDs) were prepared using d‐/l‐penicillamine (d‐/l‐Pen). The anisotropy factor of d/l‐QDs was as high as 0.01. The d/l‐QDs can be used as photocatalysts to cleave proteins. Notably, the l‐QDs displayed the highest catalytic performance under left‐circularly polarized light irradiation. Mechanistic investigations indicate the generation of hydroxyl radicals as the reactive species that cause the cutting of proteins.

Abstract The accumulation and deposition of β‐amyloid (Aβ) plaques in the brain is considered a potential pathogenic mechanism underlying Alzheimer's disease (AD). Chiral l/d ‐Fe x Cu y Se nanoparticles (NPs) were fabricated that interfer with the self‐assembly of Aβ42 monomers and trigger the Aβ42 fibrils in dense structures to become looser monomers under 808 nm near‐infrared (NIR) illumination. d ‐Fe x Cu y Se NPs have a much higher affinity for Aβ42 fibrils than l ‐Fe x Cu y Se NPs and chiral Cu 2− x Se NPs. The chiral Fe x Cu y Se NPs also generate more reactive oxygen species (ROS) than chiral Cu 2− x Se NPs under NIR‐light irradiation. In living MN9D cells, d ‐NPs attenuate the adhesion of Aβ42 to membranes and neuron loss after NIR treatment within 10 min without the photothermal effect. In‐vivo experiments showed that d ‐Fe x Cu y Se NPs provide an efficient protection against neuronal damage induced by the deposition of Aβ42 and alleviate symptoms in a mouse model of AD, leading to the recovery of cognitive competence.

A novel biosensor for ultrasensitive detection of prostate-specific antigen (PSA) was established based on gold nanorod (Au NR) dimers assembly. The circular dichroism signal was significantly amplified by a silver shell depositing on the surface of the Au NR dimers. A low limit of detection of 0.076 aM and high specificity were observed within the range of 0.1 to 50 aM target PSA. The developed biosensor has the potential to serve as a general platform for the detection of cancer biomarkers.

Abstract A colloidal gold immunochromatographic assay based on a generic monoclonal antibody is developed for the simultaneous detection of benzimidazoles and metabolite residues in milk samples. The monoclonal antibody is prepared using 2‐(methoxycarbonylamino)‐3H‐benzimidazole‐5‐carboxylic acid as the hapten, and it can recognize 11 types of benzimidazoles simultaneously. The immunochromatographic strip is assembled and labeled using gold nanoparticles. This strip can detect 11 benzimidazoles including albendazole, albendazole s‐oxide, albendazole sulfone, fenbendazole, fenbendazole sulfone, flubendazole, mebendazole, parbendazole, oxfendazole, oxibendazole, and carbendazim within 15 min in milk samples. Results are obtained visually with the naked eye, and the cutoff values and the visual limit of detection values for these benzimidazoles are 25, 6.25, 12.5, 12.5, 50, 25, 50, 50, 50, 6.25, and 25 ng mL −1 , and 6.25, 3.125, 3.125, 1.56, 12.5, 6.25, 12.5, 12.5, 6.25, 0.78, and 12.5 ng mL −1 , respectively. Results are also obtained using a hand‐held strip scan reader, with calculated limit of detection values for these benzimidazoles of 0.83, 0.77, 1.83, 0.98, 7.67, 3.50, 3.96, 5.71, 0.92, 0.59, and 1.69 ng mL −1 , respectively. In short, the developed paper sensor is a useful tool for rapid and simple screening of residues of benzimidazoles in milk samples.

In this study, we developed highly sensitive and specific monoclonal antibodies (mAbs) against estrone (E1), 17β-estradiol (17β-E2), and estriol (E3). The half-maximal inhibitory concentration values of anti-E1, anti-17β-E2, and anti-E3 mAbs were 0.46, 0.36, and 0.39 ng/mL, respectively, based on competitive enzyme-linked immunosorbent assay (ic-ELISA) results. A rapid colloidal gold-based immunoassay strip assay was developed for the determination of E1, 17β-E2, and E3 residues in milk samples. The assay had a visual cut-off value of 5 ng/mL, and required 10 min to assess with the naked eye. The results obtained from the immunochromatographic strip assay were consistent with those obtained from ic-ELISA and gas chromatography-mass spectrometry. The immunochromatographic strip assay is useful and rapid for the detection of E1, 17β-E2, and E3 in milk.

Alpha-fetoprotein (AFP) and mucoprotein1 (mucin-1) are two important disease biomarkers.

Abstract Here, Au@AgAu yolk–shell nanorods (YSNRs) with tunable plasmonic circular dichroism (PCD) responses are synthesized, for the first time, using chiral d ‐ or l ‐penicillamine. The concentration of chiral molecules and the nanogap size play key roles in the PCD signal of the YSNRs. Importantly, the PCD response could be regulated by changing the aspect ratio of gold nanorods, and the largest anisotropy factor ( g ‐factor) is 0.009. Remarkably, the YSNRs are used as new chiroptical building blocks together with Au nanoparticles (NPs) to build YSNR@NP core–satellite (CS) assemblies, which display much stronger PCD intensity and an increased g ‐factor of 0.021. The theoretical calculation data demonstrate that the significant PCD activity of nanoassemblies is originated from chiral structures and the intrinsic chirality of the building blocks. Noticeably, the developed CS superstructures with photothermal effects are utilized to quantitatively detect zinc ion in living cell lines. This study reports an emerging class of chiral inorganic nanostructures with important future applications, including enantioselective separation, asymmetric catalysis, and biomedical sensing.

In this study, we produced a sensitive and specific monoclonal antibody (mAb) against diclazuril based on a new hapten. The mAb, which belongs to the IgG2 subclass, had a 50%-inhibitory concentration of 0.36 ng/mL. A cross reactivity test revealed that the mAb had good specificity for diclazuril. A gold nanoparticle-based lateral-flow strip was assembled for the rapid screening of diclazuril in raw chicken breast and thigh samples. The strip assay had a visual limit of detection (LOD) of 2 μg/kg and a cut-off value of 20 μg/kg for diclazuril in chicken samples when evaluated with the naked eye. With the aid of a strip scan reader, the proposed assay obtained a quantitative measurement for diclazuril with an LOD of 1.08 μg/kg. Therefore, this gold nanoparticle-based lateral-flow strip assay represents a potentially useful tool for on-site detection and rapid initial screening of diclazuril in chicken samples.

Self‐assembled nanostructures have been used for the detection of numerous cancer biomarkers. In this study, a gold‐upconversion‐nanoparticle (Au‐UCNP) pyramid based on aptamers is fabricated to simultaneously detect thrombin and prostate‐specific antigen (PSA) using surface‐enhanced Raman scattering (SERS) and fluorescence, respectively. The higher the concentration of thrombin, the lower the intensity of SERS. PSA connected with the PSA aptamer leads to an increase in fluorescence intensity. The limit of detection of thrombin and PSA reaches 57 × 10 −18 and 0.032 × 10 −18 m , respectively. In addition, the pyramid also exhibits great target specificity. The results of human serum target detection demonstrate that the Au‐UCNP pyramid is an excellent choice for the quantitative determination of cancer biomarkers, and is feasible for the early diagnosis of cancer.

Organophosphorus (OP) and pyrethroid (PYR) pesticides are widely used to control various vectors and pests in agriculture, multiple industries, public health, green area servicing, and water reservoirs, among others. OP and PYR exposure cause respiratory, myocardial, and neuromuscular impairments in humans and acute toxicity in aquatic organisms and honeybees, respectively. Therefore, rapid, easy, sensitive, and quantitative OP and PYR detection methods are required. Immunoassays have been used in the detection of a variety of OP and PYR pesticides. In this review, we report the recent advances in immunoassays for detecting OPs and PYRs with an emphasis on the synthesis of haptens for immunogens and coating antigens, preparation, sensitivity, and specificity of antibodies, and extraction methods of OPs and PYRs. This review will assist in the development of sensitive and accurate analytical assays.

Ultrasensitive immunoassays, including an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and a lateral-flow immunochromatographic assay (ICA), were developed based on a monoclonal antibody for the analysis of deoxynivalenol in food and feed samples. With 0.01 M PBS, 20% ethanol–PBS, and 60% ethanol–PBS extraction, which are environmentally safe, the 50% inhibitory concentration (IC50) and limit of detection (LOD) values were 1.83–4.68 μg/kg and 0.241–0.664 μg/kg, respectively, with recovery rates of 87.7%–137% and coefficient variation values of 3.99–9.88% (intra-assay) and 4.17–9.81% (inter-assay) for the ic-ELISA relative to the results obtained by liquid chromatography–tandem mass spectrometry (LC–MS). For the ICA strip, the visual LODs were 10–150 μg/kg, the cut-off values were 50–750 μg/kg, and the calculated LODs were 1.97–46.8 μg/kg, with different sample extraction solutions, and the recovery rates were 66.7%–127%. These methods are sensitive, simple and safe, providing an auxiliary analytical tool for screening the massive samples in markets.

Abstract Heterodimers of upconversion nanoparticles (UCNPs) and gold yolk–shell nanoparticles are fabricated for the quantification of polymyxin‐B‐resistant Escherichia coli . They produce two signals, circular dichroism (CD) and upconversion luminescence (UCL). Interestingly, due to the different affinity of polymyxin B for sensitive and resistant strain, as the concentration of polymyxin B increases, the amount of UCNPs in sensitive bacteria increases sharply, increasing the intracellular UCL signal at a low polymyxin B concentration immobilized on the UCNP. The CD intensity is correspondingly reduced as the amount of UCNPs in solution decreased. Meanwhile, for polymyxin‐B‐resistant strain, the intracellular UCL increases slowly even in a high polymyxin B concentration, and the CD intensity in solution is also enhanced because of the inefficient entering of UCNP. Therefore, based on the concentration of polymyxin B coupled to the UCNPs, the levels of polymyxin‐B‐resistant bacteria can be detected with dual signals. Importantly, with 980 nm irradiation, both polymyxin‐B‐sensitive strains and polymyxin‐resistant bacteria used to induce infection in mice are detected with UCL imaging in vivo and treated well with photodynamic therapy. This novel dual‐mode heterodimer has potential utility for the advanced surveillance and control of drug‐resistant bacteria.

In this study, a sensitive monoclonal antibody (mAb) against toltrazuril (Tol) was developed based on a novel hapten. The 50% inhibitory concentrations (IC50) of toltrazuril and its metabolites ranged from 2.19 ng/mL to 4.21 ng/mL. Based on this mAb, a colorimetric paper-based sensor was developed for the rapid screening of Tol and its metabolites in samples. The proposed assay has cutoff values of <20 μg/kg for Tol and 50 μg/kg for Tol sulfone when evaluated with the naked eye, and the results could be obtained in 15 min. Quantitative results were obtained with a strip scan reader, with limits of detection <2.60 μg/kg for Tol and its metabolites in real samples. The sensitivity of both qualitative and quantitative detection meets the European Union requirements. Therefore, this strip assay provides a useful tool for the on-site detection and rapid initial screening of Tol and its derivatives in feed, egg, and chicken samples.

The development of the lateral flow assay (LFA) has received much attention in both academia and industry because of their broad applications to food safety, environmental monitoring, clinical diagnosis, and so forth. The user friendliness, low cost, and easy operation are the most attractive advantages of the LFA. In recent years, quantitative detection has become another focus of LFA development. Here, the most recent studies of quantitative LFAs are reviewed. First, the principles and corresponding formats of quantitative LFAs are introduced. In the biomaterial and nanomaterial sections, the detection, capture, and signal amplification biomolecules and the optical, fluorescent, luminescent, and magnetic labels used in LFAs are described. The invention of dedicated strip readers has drawn further interest in exploiting the better performance of LFAs. Therefore, next, the development of dedicated reader devices is described and the usefulness and specifications of these devices for LFAs are discussed. Finally, the applications of LFAs in the detection of metal ions, biotoxins, pathogenic microorganisms, veterinary drugs, and pesticides in the fields of food safety and environmental health and the detection of nucleic acids, biomarkers, and viruses in clinical analyses are summarized.

Paraquat (PQ) poisoning is a serious threat to human health that leads to pulmonary toxicity, neurotoxicity, and inflammation. Protecting humans from PQ exposure requires the development of rapid analytical methods for on-site detection. Here, two monoclonal antibodies against PQ were generated and an immunochromatographic assay (ICA) was exploited to determine PQ concentrations in water samples. The results showed that the monoclonal antibody 1D6 exhibited higher affinity and sensitivity, with an affinity constant of 5.4 × 108 mol/L and a limit of detection as low as 0.02 ng/mL. Without sample pretreatment, the developed ICA method provided visible limits of detection ranging from 0.25 to 1 ng/mL, and cut-off limits ranging from 1 to 5 ng/mL, where average recoveries were between 83.15% ± 1.9% and 94.49% ± 2.45% with a coefficient of variation ranging from 1.40% to 7.37%. Importantly, these observations were consistent with liquid chromatography tandem mass spectrometry. These data and results suggested that the ICA method was a reliable, portable, and high-throughput method for determining PQ residues in water samples.

Abstract In this study, a Cu x OS@ZIF‐8 nanostructure is fabricated to quantify the levels of hydrogen sulfide (H 2 S) in living cells and in vivo. Zeolitic lmidazolate framework‐8 (ZIF‐8) is chosen as an encapsulation shell to improve the selectivity of this probe. Using this unique nanostructure, ultrasensitive quantification and bioimaging of H 2 S in living cells are successfully achieved. The lower limit of detection is 0.8 and 5.3 nmol per 10 6 cells for circular dichroism and fluorescence modes, respectively. It is found that the chiral Cu x OS NPs transformed into achiral Cu x S NPs contribute to the ultrasensitive detection. Notably, this probe can also be carried out to detect and track H 2 S levels in tumor‐bearing animals. The discoveries put forward for the creation of a detection platform for quantitative tracking and analysis in clinic.

Abstract Senescence is a state of stable cell cycle arrest that can escape apoptosis and lead to aging and numerous age‐related diseases. In this study, an upconversion‐nanoparticle (UCNP)‐centered Au 20 –Au 30 nanoparticles tetrahedron (UAuTe) is prepared by DNA hybridization, which can selectively accelerate the clearance of senescent cells. When the beta‐2‐microglobulin antibody (anti‐B2MG) on the Au NPs recognizes senescent cells, the application of near‐infrared (NIR) light induces the disassembly of the UAuTe by breaking the boronic ester linkage. Subsequently, the Granzyme B exposed on the UCNPs induces apoptosis in senescent cells, which can then be tracked by changes in fluorescence. It is found that, as compared to single Granzyme B, the UAuTe can not only control the Granzyme B delivery by NIR‐responsivity, but also synergistically target and activate the Granzyme B in the senescent cell without the need of perforin. Moreover, this tool is applied successfully in vivo; the results demonstrate that the NIR‐responsive tetrahedron can restore renal function, tissue homeostasis, fur density, and athletic ability in a mouse model of senescence after 30 d of treatment. The NIR‐induced tetrahedron provides a practical strategy for clinical diagnosis and therapy, particularly for aging and age‐related diseases.

We developed a sensitive and rapid lateral flow immunochromatographic (LFI) assay for the simultaneous detection of fipronil and its metabolites in eggs and cucumbers using gold nanoparticle (GNP)-labeled monoclonal antibodies (mAbs). Anti-fipronil mAbs (1B6) were produced using two haptens and identified by heterologous indirect competitive enzyme-linked immunosorbent assay (icELISA) with half maximal inhibitory concentration (IC50) and limit of detection (LOD) values of 0.46 ± 0.07 and 0.05 ± 0.01 ng mL−1, respectively. The developed LFI strip showed high sensitivity and specificity in the detection of fipronil with cut-off and visual limit of detection (vLOD) values of 10 and 0.25 ng mL−1, respectively. Furthermore, the application of LFI in the detection of fipronil-spiked egg and cucumber samples was validated by liquid chromatography tandem mass spectrometry (LC-MS/MS). Our developed LFI assay is suitable for detection of fipronil and its metabolites in real samples.

Pharmaceutical and food products are fortified with pantothenic acid (PA) to address potential deficiency. Therefore, its fast, reliable, and accurate detection is of great importance to the quality control. Here, an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and a gold nanoparticle-based lateral flow immunoassay (LFIA) were established for the determination of PA based on an anti-PA monoclonal antibody (mAb). The ic-ELISA displayed a limit of detection (LOD) of 32.22 ng/mL, and the linear range was 64.44–628.84 ng/mL. Average recoveries of PA in fortified samples were 88.60–110.11% when using the ic-ELISA and a good correlation between the ic-ELISA and LC-MS/MS was obtained when analyzing samples. Furthermore, the developed LFIA strip showed a calculated LOD of 71.99, 115.80, and 240.12 ng/mL in B-complex Vitamin tablets, energy drink and infant milk powder samples, respectively. All the results demonstrated that both of these immunoassays are suitable for determining PA in pharmaceutical and food products.

Detection of cancer markers is important for early diagnosis and timely treatment of cancer. In this study, we fabricated a tailorable gold nanofilm-anodized aluminum oxide (Au-AAO) ion channel through nanoparticle self-assembly and proposed a highly sensitive and selective Mucin 1 (MUC1) detection method. By engineering the optimal layers of the Au-AAO ion channel and encoding the aptamer between the interlayers, a highly controllable ion rectification phenomenon was observed. From this, the relationship between the rectification ratio (RR) and the concentration of MUC1 was established and the highly sensitive detection of MUC1 is achieved. We found that the aptamer-modified Au-AAO ion channel has a good linear range within the MUC1 concentration of 1–104 fg mL–1 and the limit of detection (LOD) was as low as 0.0364 fg mL–1 (0.0025 aM). Thus, this research opens a new horizon for fabricating multi-functional ion channels as well as developing ultrasensitive detection technologies.

Biological application of chiral nanoparticles (NPs) has aroused enormous levels of attention over recent years. Here, we synthesized magneto-chiral cobalt hydroxide (Co(OH)2) NPs that exhibited strong chiroptical and unique magnetic properties and applied these NPs to detect and monitor reactive oxygen species (ROS) in living cells and in vivo. Circular dichroism (CD) and magnetic resonance imaging (MRI) signals of the magneto-chiral Co(OH)2 NPs exhibited a wide intracellular ROS detection range from 0.673 to 612.971 pmol/106 cells with corresponding limits of detection (LOD) at 0.087 and 0.179 pmol/106 cells, far below that of currently available probes; the LOD for d-aspartic acid coated Co(OH)2 NPs (d-Co(OH)2 NPs) was 5.7 times lower than that for l-aspartic acid coated Co(OH)2 NPs (l-Co(OH)2 NPs) based on the CD signals. In addition, d-Co(OH)2 NPs also exhibited dynamic ROS monitoring ability. The high levels of selectivity and sensitivity to ROS in complex biological environments can be attributed to the Co2+ oxidation reaction on the surface of the NPs. Furthermore, magneto-chiral Co(OH)2 NPs were able to quantify the levels of ROS in living mice by fluorescence and MRI signals. Collectively, these results reveal that magneto-chiral Co(OH)2 NPs exhibit a remarkable ability to quantify ROS levels in living organisms, and could therefore provide new tools for exploring chiral nanomaterials as a potential biosensor to investigate biological events.

To ensure food quality and prevent histamine (HA) toxicity, a rapid and direct method of detecting HA is required. In this work, we prepared a monoclonal antibody (mAb) against HA using a hapten produced by the introduction of a phenyl-containing linker. The novel mAb exhibited high sensitivity against HA as determined by ELISA, with a half-maximal inhibitory concentration of 21.51 ng/mL. A gold nanoparticle-based immunosensor was fabricated for rapid detection of HA in fish samples. After optimizing the immunosensor, a visual limit of detection (LOD) and a calculated LOD were 0.25 mg/kg and 10.48 μg/kg for HA, respectively. Recovery rates from the spiked fish samples ranged from 87.33% to 104.67% with the coefficient of variation below 10.82%. Concurrently, the whole process in testing real sample was completed within 15 min, and all results were well confirmed and comparable by liquid chromatography-mass spectrometry and the commercial test strip. These data revealed that the proposed immunosensor could be used as a monitoring tool for the rapid and direct detection of HA in fish samples.

Tadalafil (TDL) is an illegal additive drug found in drinks and functional foods that could threaten public health. There was a great concern whether the adulteration occurred in coffee added with similar type of herbs. Here we have developed a rapid, simple, sensitive, and semi-quantitative lateral flow immunoassay (LFIA) based on gold and fluorescence labelled monoclonal antibody (mAb) for detection of TDL in coffee sample. Under optimal conditions, the cut off limits using gold nanoparticles labelled mAb (GLM) was found to be 250 ng/mL and 100 ng mL using fluorescent labelled mAb (FLM) in coffee samples. The coffee samples were spiked with TDL, and the LFIA with GLM gave average recoveries of 92–105.3% (intra-assay) and 96.6–105.9% (inter-assay), meanwhile with FLM gave recoveries 97.9–107.3% (intra-assay) and 98.3–108.9% (inter-assay). Results gave LFIA with FLM more sensitive than with GLM and all the test can be completed within 10 min, which would be an option for convenient and rapid assay of TDL detection.

The differentiation of neural stem cells via nanomaterials has attracted attention and has become a potential tool. However, the chirality effect in neural stem cell differentiation has not been investigated. Here, this study shows that chiral nanoparticles (NPs) with strong chirality can efficiently accelerate the differentiation of mouse neural stem cells (NSCs) into neurons under near-infrared (NIR) light illumination. L-type NPs are 1.95 times greater than D-type NPs in promoting NSCs differentiation due to their 1.47-fold endocytosis efficiency. Whole gene expression map analysis reveals that circularly polarized light illumination and chiral NPs irradiation significantly upregulate Map2, Yap1, and Taz genes, resulting in mechanical force, cytoskeleton protein action, and accelerated NSCs differentiation. In vivo experiments show that successful differentiation can further alleviate symptoms in Alzheimer's disease mice. Moreover, the clearance of L-type NPs on amyloid and hyperphosphorylated p-tau protein reachs 68.24% and 66.43%, respectively, under the synergy of NIR irradiation. The findings suggest that strong chiral nanomaterials may have advantages in guiding cell development and can be used in biomedicine.

In the rapidly expanding fields of nanoscience and nanotechnology, there is considerable interest in chiral nanomaterials, which are endowed with unusually strong circular dichroism. In this review, we summarize the principles of organization underlying chiral nanomaterials and generalize the recent advances in the main strategies used to fabricate these nanoparticles for bioscience applications. The creation of chirality from nanoscale building blocks has been investigated both experimentally and theoretically, and the tunability of chirality using external fields, such as light and magnetic fields, has allowed the optical activity of these materials to be controlled and their properties understood. Therefore, the specific recognition and potential applications of chiral materials in bioscience are discussed. The effects of the chirality of nanostructures on biological systems have been exploited to sense and cut molecules, for therapeutic applications, and so on. In the final part of this review, we examine the future perspectives for chiral nanomaterials in bioscience and the challenges posed by them.

Enrofloxacin, a veterinary antibiotic that persists in food, poses a risk to human health. Here, a monoclonal antibody against enrofloxacin, 1H12, was prepared based on the hapten ENR-1, and showed excellent sensitivity with a 50% inhibitory concentration (IC50) of 0.03 ng/mL. Using this antibody, 2 lateral-flow immunochromatographic assays were developed for determination of enrofloxacin in egg, milk, honey, and chicken meat samples. The detection ranges (IC20-IC80) were 0.16-0.82 ng/g, 0.24-1.8 ng/g, 0.25-3.6 ng/g, and 0.61-3.9 ng/g by colloidal gold-immunochromatographic sensor (CG-ICS) analysis, and 0.022-0.42 ng/g, 0.054-0.42 ng/g, 0.069-1.4 ng/g, and 0.19-2.2 ng/g by Eu-fluorescence-immunochromatographic sensor (EF-ICS) analysis. The intraassay and interassay recovery rates were 88.9 to 108.5% with coefficients of variation of 1.3 to 7.0% by CG-ICS analysis, and 88.6 to 113.6% with coefficients of variation of 1.3 to 8.1% by EF-ICS analysis. Thus, our newly developed ICS are sensitive and reliable, providing an option for rapid quantitative detection of enrofloxacin in food samples.

Propamocarb is a carbamate fungicide used to control Phytophthora disease. Frequent and large-scale use of propamocarb means that it poses a potential threat to the health of consumers. Monoclonal antibodies against propamocarb were prepared using a hapten of propamocarb that was generated by introducing a benzene ring and a carboxyl group into the structure of propamocarb. A lateral flow immunoassay strip was developed for the detection of propamocarb in tomato and cucumber samples using the gold nanoparticle-labeled antibody. The immunoassay strip was found to provide a visible limit of detection was 5 ng/g and the cut-off value was 250 ng/g for propamocarb in food samples. For quantitative analysis, the calculated limits of detection (LODs) of the immunoassay strip were 1.43 ng/g and 0.44 ng/g in cucumber and tomato, respectively. Using the immunoassay strip, the average recoveries ranged from 95.5 ± 5.4% to 108.8 ± 6.8%, with CVs of 3.1-6.2% for the cucumber, and the average recoveries were 95.1 ± 6.5%-111.9 ± 4.2%, with CVs ranging from 3.7% to 6.8% for tomato samples. All the results demonstrated that the immunoassay strip was suitable for the detection of propamocarb in fruits and vegetables.

Isoprothiolane (IPT) is widely used to control rice blast, but can cause unacceptable harm to organisms making its detection in rice crucial. In this work, a hapten based on the structure of IPT was produced to prepare a monoclonal antibody (mAb) with high sensitivity and specificity. The half maximum inhibitory concentration of the anti-IPT mAb was 0.81 ng/mL as determined by ELISA, and the cross reactivity with analogues was negligible. A GNP-based lateral flow immunoassay (LFIA) method was subsequently developed to quantitatively detect IPT in brown and polished rice. The optimized LFIA, in brown rice samples, showed a visual limit of detection, cut-off value and calculated limit of detection of 2 mg/kg, 10 mg/kg and 81 ug/kg, respectively and 0.2 mg/kg, 4 mg/kg and 66 ug/kg in polished rice samples. Recovery rates in spiked brown and polished rice were 95.21 %–103.06 % and 91.05 %–104.13 %, with a coefficient of variation of 1.25 %–4.17 % and 2.93 %–8.42 %, respectively. No significant difference in recovery rates were seen between LFIA and LC-MS/MS indicating that the prepared GNP-based LFIA had good potential for the detection of IPT in rice.

Wheat gliadin is one of the most important causes of gluten sensitivity. This study aimed to develop a sandwich enzyme-linked immunosorbent assay (ELISA) and gold nanoparticle-based lateral flow (LFIA) strips to detect wheat allergen in food. Through cell screening, ten monoclonal antibodies (mAbs) against gliadin and after optimization were obtained, a pair of mAbs suitable for its detection (capture antibody: mAb 7; detection antibody: HRP-labeled mAb 6) were identified. Based on two of these antibodies, a sandwich ELISA with limit of detection (LOD) of 60 ng/mL in negative milk, and more importantly, negligible cross-reactivity to other allergens was developed. The average recoveries for gliadin in negative milk were 99.16%–100.07% using the sandwich ELISA. We also developed LFIA strips for the rapid detection of gliadin with visual limit of detection (vLOD) of 25 ng/mL and calculated LOD value of 6.56 ng/mL in negative milk. The test results of positive samples obtained from the LFIA strips were highly consistent with those of the sandwich ELISA. Thus, the developed LFIA strip is an effective and reliable tool for the rapid and on-site detection of wheat allergen in milk.

An immunochromatographic test strip method for detecting A29 was established. The strips utilizing mAb-7C5 and 5D8 showed the best sensitivity with the lowest LOD, 50 pg mL −1 for A29.

In this study, a hapten of methomyl was designed and used to produce monoclonal antibodies (mAbs) against methomyl. Based on these mAbs, we developed an enzyme-linked immunosorbent assay (ELISA) and immunochromatographic assay (ICA) strip for the determination of methomyl residues. Results from the ELISA showed that mAb 1D10 exhibited higher affinity with an affinity constant of 2.76 × 1010 L/mol and higher sensitivity with a limit of detection (LOD) was 8.12 ng/mL. After optimizing the ICA, a visible limit of detection (vLOD) was found to be 100 ng/g and the cut-off value was 500 ng/g for methomyl in cabbage and tomato. The calculated LODs were 3.2 ng/g and 5.4 ng/g in cabbage and tomato, respectively. Moreover, results from the ICA were consistent with those of the ELISA in our recovery assay using spiked samples. Hence, the ICA method has a bright future and great prospects for the detection of methomyl in food samples.

Foodborne pathogens cause diseases in humans. The traditional methods of detecting foodborne pathogens are time-consuming. The lateral flow immunoassay (LFIA) has become a widely used detection platform for onsite testing of various foodborne pathogens due to its time-efficiency, cost-effectiveness, portability, and ease of use. With the development of novel nanomaterials, the sensitivity of the LFIA has improved tremendously compared with traditional colorimetric LFIA sensors. This review first summarizes the principles and corresponding formats of the LFIA. Then, a detailed classification of nanomaterial label (e.g., metallic, carbon and selenium, fluorescent, and magnetic nanoparticles) synthesis, signal amplification strategy, and detection principles are discussed as related to food safety. Subsequently, the LFIA used in the detection of pathogenic bacteria, including Escherichia coli, Vibrio parahaemolyticus, Staphylococcus aureus, Listeria monocytogenes, and Salmonella, are classified and summarized. Multiple signal modes have been explored that improve the sensitivity of foodborne pathogen detection. Further improvement should focus on the design and preparation of high signal-to-noise ratio nanomaterials to achieve highly sensitive detection, and multitarget and multimode sensing.

Chlordimeform (CDM) is a broad-spectrum and highly effective insecticide and acaricide used to control pests in agriculture. We produced two monoclonal antibodies (mAbs) against CDM and developed an immunochromatographic assay to screen CDM in cucumbers and tomatoes. MAb 4A3 had high sensitivity with a 50% inhibitory concentration of 0.287 ng mL-1. The assay had a cut-off value of 25 μg kg-1 and a visual limit of detection (vLOD) of 1 μg kg-1 in cucumbers and a cut off value of 50 μg kg-1 and a vLOD of 2.5 μg kg-1 in tomatoes. The calculated limit of detection (cLOD) in cucumbers and tomatoes was 0.115 μg kg-1 and 0.215 μg kg-1, respectively. The recovery rates were 97.9% to 106.9% for cucumbers and 97.8% to 107.4% for tomatoes, consistent with the results obtained from indirect competitive ELISA. Our findings showed that the immunochromatographic assay is an efficient and accurate method for CDM detection in cucumbers and tomatoes.

In this study, a sensitive monoclonal antibody (mAb) 1B5 against eugenols was prepared based on a novel hapten. Based on this mAb, a paper-based lateral-flow immunoassay (LFIA) was developed using Eu-fluorescent microspheres sensor, that could achieve qualitative and quantitative detection of eugenols within 10 min. Results showed colorimetric values observed by the naked eye were 12.3 µg/kg, 12.3 µg/kg, 37 µg/kg and 111 µg/kg for eugenol, isoeugenol, methyl eugenol, and methyl isoeugenol, respectively, in both water and fish samples. For quantitative detection of eugenol, isoeugenol, methyl eugenol and methyl isoeugenol, the detection ranges were 4.49-48.4 µg/kg, 6.02-66.8 µg/kg, 16.5-150 µg/kg and 47.9-710 µg/kg in water, and 3.9-30.9 µg/kg, 5.9-62.6 µg/kg, 16.7-255 µg/kg, and 44.5-890 µg/kg in fish, respectively. The recovery test and detection in fish demonstrated the reliability of the LFIA in real samples. Therefore, the developed LFIA produced a promising alternative tool for the rapid on-site detection of eugenols.

Torasemide is a new loop diuretic agent added illegally to health foods for weight loss, which can result in serious health risks for consumers. A rapid and sensitive immunochromatographic assay for detection of torasemide (ICA) based on a new monoclonal antibody (mAb) was developed. The mAb IC50 for torasemide was 0.93 ng/mL, and the mAb did not cross-react with other analogues. In PBS, the cut-off value and limit of detection were 1 ng/mL and 0.11 ng/mL, respectively, with a linear range between 0.61 and 6.13 ng/mL. In slimming tablet and capsule samples, the cut-off value was 5 ng/g. Recoveries were 101.1% ± 1.7%-106.1% ± 1.3% in tablet samples and 101.2% ± 2.2%-109.1% ± 3.9% in capsule samples, with coefficients of variation 2.1%-3.1% and 1.8%-3.6%, respectively, consistent with existing LC-MS/MS methods. Therefore, the ICA is suitable for use in slimming tablet and capsule samples.

In this work, we report the application of gold nanorods ladder assemblies as chiroptical sensors for detecting mercury ions (Hg2+). By taking advantage of the Hg2+-mediated T–T base pair of DNA and the high sensitivity of CD measurements, the method offers a simple and sensitive detection of target Hg2+ residues in water. Therefore, the developed method will be a promising tool for monitoring heavy metal ions, other small molecules and biomacromolecules.

A universal chirality detection platform based on immuno-recognition-driven nanoparticle assembly has been fabricated for the first time. A strong shifted chiral signal was produced by asymmetric plasmonic nanoparticle dimers. Using bisphenol A (BPA) as a model target substrate, the LOD was 0.02 ng mL(-1).

Organization of nanoparticles (NPs) of different materials into superstructures of higher complexity represents a key challenge in nanotechnology. Polymerase chain reaction (PCR) was used in this study to fabricate chains consisting of plasmonic NPs of different sizes, thus denoted heterochains. The NPs in such chains are connected by DNA oligomers, alternating in a sequence big-small-big-small-... and spanning lengths in the range of 40-300 nm by varying the number of PCR cycles. They display strong plasmonic chirality at 500-600 nm, the chiral activity revealing nonmonotonous dependence on the length of heterochains. We find the strength of surface-enhanced Raman scattering (SERS) to increase with chain length, while the chiral response initially increased and then decreased with the number of PCR cycles. The relationship between the optical properties of the heterochains and their structure/length is discussed. The length-dependent intense optical response of the plasmonic NP heterochains holds great potential for biosensing applications.

In this study, we report a new fluorogenic sensor based on fluorescence resonance energy transfer (FRET) for detection of heavy metal ions in aqueous solution. The method showed the advantage of being simple, highly sensitive and selective, and rapid. The donor (CdTe QDs) and acceptor (TAMRA or Cy5) are brought into close proximity to one another due to Hg2+ and Ag+ form strong and stable T-Hg2+-T complexes and C-Ag+-C complexes, which quenches the fluorescent intensity of CdTe QDs and enables the energy transfer from donor to acceptor. This sensor showed high sensitivity and selectivity when only one kind of ion (Ag+ or Hg2+) exists. Furthermore, the assay can also simultaneously detect Ag+ and Hg2+ in water media with the limit of detection (LOD) of 2.5 and 1.8 nM, separately, which satisfactorily meets the sensitivity demands of Environmental Protection Agency (EPA) and World Health Organization (WHO). This assay also exhibits excellent selectivity toward Ag+ and Hg2+. Therefore, this method is of great practical and theoretical importance for detecting heavy metal ions in aqueous solution.

The strong plasmonic chiroptical activities of gold core‐DNA‐silver shell nanoparticles (NPs) are reported for the first time, using cytosine‐rich single‐stranded DNA as the template for the guidance of silver shell growth. The anisotropy factor of the optically active NPs at 420 nm reaches 1.93 × 10 −2 . Their chiroptical properties are likely induced by the DNA–plasmon interaction and markedly amplified by the strong electromagnetic coupling between the gold core and silver shell.

A rapid, simple, and sensitive immunochromatographic test strip has been developed for testing residues of ciprofloxacin (CIP). A specific and sensitive monoclonal antibody (mAb) for CIP was generated by immunizing BALB/c mice with well-characterized CIP-Keyhole limpet haemocyanin. Under the optimized conditions, the cut-off limits of test strips for CIP were found to be 5 ng/mL in phosphate-buffered saline and 2.5 ng/mL in milk samples. Each test can be evaluated within 3 min. The cross-reactivities of the CIP test strip to enrofloxacin (ENR), norfloxacin (NOR), nadifloxacin (NDF), danofloxacin (DANO), pefloxacin (PEX), lomefloxacin (LOME), enoxacin (ENO), and sarafloxacin (SAR) were 71.4%, 71.4%, 66%, 50%, 33%, 20%, 12.5%, and 6.25%, respectively. The data indicate that the method is sensitive, specific, and has the advantages of simplicity and speed, therefore, this test strip is a useful screening method for the detection of CIP residues in milk samples.