Luis M. Liz‐Marzán

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.

Within the field of nanotechnology, nanoparticles are one of the most prominent and promising candidates for technological applications. Self-assembly of nanoparticles has been identified as an important process where the building blocks spontaneously organize into ordered structures by thermodynamic and other constraints. However, in order to successfully exploit nanoparticle self-assembly in technological applications and to ensure efficient scale-up, a high level of direction and control is required. The present review critically investigates to what extent self-assembly can be directed, enhanced, or controlled by either changing the energy or entropy landscapes, using templates or applying external fields.

This article provides an overview of current research into the synthesis and properties of gold nanorods. Interest in rod-shaped nanoparticles stems from their unique optical properties, which can be approximated by Mie–Gans theory. We begin by outlining briefly the origin of the shape-dependent optical properties of rods. The different synthetic strategies that have been developed to achieve decent yields and sample monodispersity are then described, and the methods used for physical characterization as well as results of inorganic structure studies follow. Some of the most innovative research dealing with surface modification and chemical reactivity of gold nanorods is highlighted, together with new directions such as the synthesis of core-shell particles and the interactions of gold nanorods with biomolecules. Gold nanorods can be excited by ultrafast laser-induced heating; the resulting relaxation processes are important in determining the material properties of the metal particles. In addition, vibrational modes and shape changes are elucidated, and a theoretical analysis of the expected behavior is also presented. The incorporation of the gold nanorods into thin films and gels provides a new avenue for designing and growing materials with anisotropic optical properties. Initial results on the optical properties of such nanocomposites are reviewed. This review is concluded with a section devoted to the future perspectives for gold rods as novel materials.

In this tutorial review, we summarise recent research into the controlled growth of gold nanoparticles of different morphologies and discuss the various chemical mechanisms that have been proposed to explain anisotropic growth. With the overview and discussion, we intended to select those published procedures that we consider more reliable and promising for synthesis of morphologies of interest. We expect this to be interesting to researchers in the wide variety of fields that can make use of metal nanoparticles.

Gold colloids have been homogeneously coated with silica using the silane coupling agent (3-aminopropyl)trimethoxysilane as a primer to render the gold surface vitreophilic. After the formation of a thin silica layer in aqueous solution, the particles can be transferred into ethanol for further growth using the Stöber method. The thickness of the silica layer can be completely controlled, and (after surface modification) the particles can be transferred into practically any solvent. Varying the silica shell thickness and the refractive index of the solvent allows control over the optical properties of the dispersions. The optical spectra of the coated particles are in good agreement with calculations using Mie's theory for core−shell particles.

Metal nanoparticles can be used as building blocks for the formation of nanostructured materials. For the design of materials with specific (optical) properties, several approaches can be followed, even when starting from the very same basic units. In this article, a survey is provided of the optical properties of noble metal nanoparticles, specifically gold, silver, and their combinations, prepared in solution through colloid chemical methods. The optical properties are shown to be mainly influenced by the surface plasmon resonance of conduction electrons, the frequency of which is not only determined by the nature of the metal but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. Recent results showing how these various parameters affect the optical properties are reviewed. The results highlight the high degree of control that can now be achieved through colloid chemical synthesis.

This tutorial review presents an overview of theoretical methods for predicting and understanding the optical response of gold nanoparticles. A critical comparison is provided, assisting the reader in making a rational choice for each particular problem, while analytical models provide insights into the effects of retardation in large particles and non-locality in small particles. Far- and near-field spectra are discussed, and the relevance of the latter in surface-enhanced Raman spectroscopy and electron energy-loss spectroscopy is emphasized.

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

Wet chemistry in organic solvents has proven highly efficient for the preparation of several types of metallic, metal-oxide, and semiconductor nanostructures. This Short Review focuses on the use of oleylamine (OAm) as a versatile reagent for the synthesis of various nanoparticle systems. We describe the ability of OAm to act as a surfactant, solvent, and reducing agent, as a function of other synthesis parameters. We also discuss the specific role of OAm either alone or in combination with other reactants, to form nanostructures using a variety of organic or inorganic compounds as precursors. In certain cases OAm can form complex compounds with the metal ions of the corresponding precursor, leading to metastable compounds that can act as secondary precursors and thus be decomposed in a controlled way to yield nanoparticles. We also point out that OAm-stabilized particles can often be dispersed in different organic solvents yielding solutions with enhanced colloidal stability over long times and the potential to find applications in a number of different fields.

Catalysis by metallic nanoparticles is certainly among the most intensely studied problems in modern nanoscience. However, reliable tests for catalytic performance of such nanoparticles are often poorly defined, which makes comparison and benchmarking rather difficult. We tackle in this tutorial review a subset of well-studied reactions that take place in aqueous phase and for which a comprehensive kinetic analysis is available. Two of these catalytic model reactions are under consideration here, namely the reduction of (i) p-nitrophenol and (ii) hexacyanoferrate (iii), both by borohydride ions. Both reactions take place at the surface of noble metal nanoparticles at room temperature and can be accurately monitored by UV-vis spectroscopy. Moreover, the total surface area of the nanoparticles in solution can be known with high precision and thus can be directly used for the kinetic analysis. Hence, these model reactions represent cases of heterogeneous catalysis that can be modelled with the accuracy typically available for homogeneous catalysis. Both model reactions allow us to discuss a number of important concepts and questions, namely the dependence of catalytic activity on the size of the nanoparticles, electrochemistry of nanoparticles, surface restructuring, the use of carrier systems and the role of diffusion control.

Polygonal (mainly triangular) silver nanoprisms were synthesized by boiling AgNO3 in N,N-dimethyl formamide, in the presence of poly(vinylpyrrolidone). Although during the synthesis, a mixture of nanoprisms and nanospheroids is formed, the latter can be removed through careful centrifugation. The UV−visible spectra of the nanoprisms display an intense in-plane dipolar plasmon resonance band, as well as weak bands for in-plane and out-of-plane quadrupolar resonances. The nanoprisms are also stable in other solvents, such as ethanol and water, and solvent exchange leads to strong shifts of the in-plane dipole plasmon band.

Multipod Au nanoparticles (nanostars) with single crystalline tips were synthesized in extremely high yield through the reduction of HAuCl4 in a concentrated solution of poly(vinylpyrrolidone) (PVP) in N,N-dimethylformamide (DMF), in the presence of preformed Au nanoparticle seeds, but with no need for external energy sources. Nanostar dispersions display a well-defined optical response, which was found (through theoretical modeling) to comprise a main mode confined within the tips and a secondary mode confined in the central body. Calculations of the surface enhanced Raman scattering (SERS) response additionally show that this morphology will be relevant for sensing applications.

SERS permits identifying the nature of molecules in extremely low concentrations, but it is hindered by poor enhancement or low reproducibility. We demonstrate controllable approximately 10(10) signal amplification reaching the zeptomol detection limit for a nonresonant molecule by sandwiching the analyte between the tips of star-shaped gold nanoparticles and a planar gold surface using a simple synthetic procedure. This unprecedented control over light-intensity amplification opens a new avenue toward high-yield, fully reproducible, SERS-based, zeptomol detection and holds promise for nonlinear optics applications at the single-particle level.

Au nanotriangles display interesting nanoplasmonic features with potential application in various fields. However, such applications have been hindered by the lack of efficient synthetic methods yielding sufficient size and shape monodispersity, as well as by insufficient morphological stability. We present here a synthesis and purification protocol that efficiently addresses these issues. The size of the nanotriangles can be tuned within a wide range by simply changing the experimental parameters. The obtained monodispersity leads to extended self-assembly, not only on electron microscopy grids but also at the air-liquid interface, allowing transfer onto centimeter-size substrates. These extended monolayers show promising performance as surface-enhanced Raman scattering substrates, as demonstrated for thiophenol detection.

Gold nanostars are multibranched nanoparticles with sharp tips, which display extremely interesting plasmonic properties but require optimization. We present a systematic investigation of the influence of different parameters on the size, morphology, and monodispersity of Au nanostars obtained via seeded growth in concentrated solutions of poly(vinylpyrrolidone) in N,N-dimethylformamide. Controlled prereduction of Au(3+) to Au(+) was found to influence monodispersity (narrower plasmon bands), while the [HAuCl(4)]/[seed] molar ratio significantly affects the morphology and tip plasmon resonance frequency. We also varied the size of the seeds (2-30 nm) and found a clear influence on the final nanostar dimensions as well as on the number of spikes, while synthesis temperature notably affects the morphology of the particles, with more rounded morphologies formed above 60 °C. This rounding effect allowed us to confirm the importance of sharp tips on the optical enhancing behavior of these nanoparticles in surface-enhanced raman scattering (SERS). Additionally, the sensitivity toward changes in the local refractive index was found to increase for larger nanostars, though lower figure of merit (FOM) values were obtained because of the larger polydispersity.

Anisotropy in plasmonic metal nanoparticles plays a major role in the enhancement of the Raman scattering of adsorbed molecules.

The use of nanometre thick silica shells as a means to stabilize metal clusters and semiconductor particles is discussed, and its potential advantages over conventional organic capping agents are presented. Shell deposition depends on control of the double layer potential, and requires priming of the core particle surface. Chemical reactions are possible within the core, via diffusion of reactants through the shell layer. Quantum dots can be stabilized against photochemical degradation through silica deposition, whilst retaining strong fluorescence quantum yields and their size dependent optical properties. Ordered 3D and 2D arrays of a macroscopic size with uniform particle spacing can be created. Thin colloid films can also be created with well-defined interparticle spacing, allowing controlled coupling of exciton and surface plasmon modes to be investigated. A number of future core–shell nanocomposite structures are postulated, including quantum bubbles and single electron capacitors based on Au@SiO2.

Highly organized supercrystals of Au nanorods with plasmonic antennae enhancement of electrical field have made possible fast direct detection of prions in complex biological media such as serum and blood. The nearly perfect three-dimensional organization of nanorods render these systems excellent surface enhanced Raman scattering spectroscopy substrates with uniform electric field enhancement, leading to reproducibly high enhancement factor in the desirable spectral range.

Gold nanoparticles (NPs) were prepared by reduction with salicylic acid in aqueous solution. The resulting dispersions were found to contain a mixture of flat triangular/hexagonal and smaller close-to-spherical NPs. As expected from theoretical considerations, such nanocolloids display two clearly differentiated surface plasmon bands at 540 and 860 nm associated with spherical and anisotropic triangular/hexagonal NPs, respectively. Layer-by-layer (LBL) assembly was used to deposit thin films of the Au colloids. UV−visible data indicate preferential adsorption of the flat particles on polyelectrolyte films. Importantly, a new band developed at 650 nm as the number of the Au NPs bilayers increased. This finding indicates that there exists a strong interaction between the NPs in adjacent layers, resulting in the surface plasmon absorption at a new wavelength. The insertion of extra polyelectrolyte or montmorillonite layers between the Au bilayers was shown to gradually reduce the interlayer interaction and resulted in the NP composite films with absorption spectra virtually identical to those of the original dispersion. The bilayer deposition sequence in LBL assembly, i.e. multilayer architecture, can be used to control the strength of NP−NP coupling in the layered composites.

The preparation and chemical reactivity of Ag@SiO2 particles have been investigated using UV−vis spectroscopy, laser Doppler electrophoresis, and electron microscopy. The factors governing the deposition of silica onto silane-primed silver particles have been investigated and the deposition conditions (pH and reagent concentrations) optimized. It is demonstrated that the thin silica shells deposited from aqueous/ethanolic sodium silicate solutions are porous. Silver cores dissolve in alkaline cyanide solutions, with the rate depending on the shell thickness. Ag2S@SiO2 can be prepared following exposure to sulfide ion, while silica-coated alloys of silver and gold can be prepared by reaction of Ag@SiO2 with AuCl4-. The kinetics of these core reactions with solution reagents is governed by their rate of diffusion through the shell. A diffusion coefficient of 10-12 cm2 s-1 is estimated for cyanide ion diffusing through non-heat-treated silica shells.

Lowering the limit of detection is key to the design of sensors needed for food safety regulations, environmental policies and the diagnosis of severe diseases. However, because conventional transducers generate a signal that is directly proportional to the concentration of the target molecule, ultralow concentrations of the molecule result in variations in the physical properties of the sensor that are tiny, and therefore difficult to detect with confidence. Here we present a signal-generation mechanism that redefines the limit of detection of nanoparticle sensors by inducing a signal that is larger when the target molecule is less concentrated. The key step to achieve this inverse sensitivity is to use an enzyme that controls the rate of nucleation of silver nanocrystals on plasmonic transducers. We demonstrate the outstanding sensitivity and robustness of this approach by detecting the cancer biomarker prostate-specific antigen down to 10(-18) g ml(-1) (4 × 10(-20) M) in whole serum.

Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most powerful analytical techniques for identification of molecular species, with the potential to reach single-molecule detection under ambient conditions. This Concept article presents a brief introduction and discussion of both recent advances and limitations of SERS in the context of diagnosis and biodetection, ranging from direct sensing to the use of encoded nanoparticles, in particular focusing on ultradetection of relevant bioanalytes, rapid diagnosis of diseases, marking of organelles within individual cells, and non-invasive tagging of anomalous tissues in living animals.

This Feature Article provides an overview of current research on the synthesis and properties of silver nanoplates. Starting from a brief description of the origin of the optical properties of Ag nanoparticles and the factors affecting them, we introduce the numerical methods used for modelling—discrete dipole approximation (DDA) and boundary element method (BEM)—and present a comparative study between theoretical predictions and experimental results. Then, the principal physical and wet-chemical synthetic protocols that have been used to obtain Ag nanotriangles/nanoplates in high yield are described, with a discussion of the formation mechanisms proposed by the different authors. Subsequently, the structural characterization of the particles is described, followed by a section devoted to the reactivity and stability of silver nanoplates. We conclude with a description of potential applications in the field of biological and chemical sensors and surface enhanced Raman spectroscopy (SERS).

ADVERTISEMENT RETURN TO ISSUEPREVViewpointNEXTA “Tips and Tricks” Practical Guide to the Synthesis of Gold NanorodsLeonardo Scarabelli*†, Ana Sánchez-Iglesias†, Jorge Pérez-Juste‡, and Luis M. Liz-Marzán*†§View Author Information† Bionanoplasmonics Laboratory, CIC biomaGUNE, Paseo de Miramon 182, 20009 Donostia-San Sebastian, Spain‡ Departamento de Quı́mica Fı́sica, Universidade de Vigo, 36310 Vigo, Spain§ Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain*E-mail: [email protected] (L.S.).*E-mail: [email protected] (L.M.L.-M.).Cite this: J. Phys. Chem. Lett. 2015, 6, 21, 4270–4279Publication Date (Web):November 5, 2015Publication History Published online5 November 2015Published inissue 5 November 2015https://doi.org/10.1021/acs.jpclett.5b02123Copyright © 2015 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views34136Altmetric-Citations298LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (5 MB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Absorption,Gold,Nanoparticles,Nanorods,Redox reactions Get e-Alerts

A method for controlled and homogeneous silica coating of low-aspect-ratio CTAB-stabilized gold nanorods has been developed through the combination of the LBL technique and the Stöber method. Hydrophobation of the gold nanoparticles was achieved via surface functionalization with a hydrophobic silane coupling agent.

Abstract The versatility of wet chemical methods has rendered them extremely popular for the preparation of metal nanoparticles with tailored size and shape. This Feature Article reviews the use of N , N ‐dimethylformamide (DMF) for the reduction of metal salts, mainly Au and Ag, while also acting as a solvent. Apart from describing the ability of DMF to reduce metal salts, the effect of different parameters, such as the concentration of capping agent and metal precursors, the presence of preformed seeds acting as catalysts or their crystalline structure, on particle morphology are analyzed. Published reports on the use of different capping agents are summarized, with particular emphasis on the role of poly(vinylpyrrolidone) to determine the morphology of the particles. Finally, a brief overview is provided on the modulation of the optical response in DMF‐based metal nanoparticle colloids with tunable size and shape.

Research on metal nanoparticles has been boosted by a wide variety of applications that often require a precise definition of the morphological features at the nanometer scale. Although the preparation (often based on colloid chemistry) of metal nanoparticles with many different shapes and sizes has been developed and optimized for spheres, rods, cubes, platelets and other shapes, the last few years have seen a rising interest in branched morphologies. This review article describes the main synthetic processes for the fabrication of such branched nanoparticles, often termed as nanostars, as well as some of the principal applications that have been found. A special emphasis is given to optical properties related to localized surface plasmon resonances and surface enhanced spectroscopies, for which nanostars have been predicted and demonstrated to shine brighter than any other shapes, thus opening new avenues for highly sensitive detection or biolabelling, among other applications.

Core–shell particles with tailored optical properties are obtained via manipulation of the number of Au@SiO2 nanoparticle layers deposited onto larger polymer spheres. The surface characteristics of silica, which surrounds the gold nanoparticles, are exploited to achieve a dense and uniform nanoparticle coating. The layer-by-layer (LbL) self-assembly technique yet again proves to be a worthy asset for the preparation of these novel metal-based core–shell and hollow colloids (see Figure).

Hydrophobic interactions constitute one of the most important types of nonspecific interactions in biological systems, which emerge when water molecules rearrange as two hydrophobic species come close to each other. The prediction of hydrophobic interactions at the level of nanoparticles (Brownian objects) remains challenging because of uncontrolled diffusive motion of the particles. We describe here a general methodology for solvent-induced, reversible self-assembly of gold nanoparticles into 3D clusters with well-controlled sizes. A theoretical description of the process confirmed that hydrophobic interactions are the main driving force behind nanoparticle aggregation.

The capacity to respond or adapt to environmental changes is an intrinsic property of living systems that comprise highly-connected subcomponents communicating through chemical networks. The development of responsive synthetic systems is a relatively new research area that covers different disciplines, among which nanochemistry brings conceptually new demonstrations. Especially attractive are ligand-protected gold nanoparticles, which have been extensively used over the last decade as building blocks in constructing superlattices or dynamic aggregates, under the effect of an applied stimulus. To reflect the importance of surface chemistry and nanoparticle core composition in the dynamic self-assembly of nanoparticles, we provide here an overview of various available stimuli, as tools for synthetic chemists to exploit. Along with this task, the review starts with the use of chemical stimuli such as solvent, pH, gases, metal ions or biomolecules. It then focuses on physical stimuli: temperature, magnetic and electric fields, as well as light. To reflect on the increasing complexity of current architectures, we discuss systems that are responsive to more than one stimulus, to finally encourage further research by proposing future challenges.

Anisotropic (nonspherical) metal nanoparticles are of widespread research interest because changing the shape of metals at the nanoscale can provide access to materials with unique optical, electronic, and catalytic properties. The development of seeded growth syntheses has provided researchers unprecedented access to anisotropic metal nanocrystals (particularly, gold, silver, platinum, and palladium nanocrystals) with precisely controlled dimensions and crystallographic features. The mechanisms by which the various reagents present in seeded growth syntheses accomplish shape control, however, have yet to be fully elucidated. Recently, the role halide ions play in controlling metal nanocrystal shape has become a subject of particular interest. There are many ways in which the halide ions may direct the anisotropic growth of metal nanocrystals, including modulating the redox potentials of the metal ions, acting as face-specific capping agents, and/or controlling the extent of silver underpotential deposition at the nanocrystal surface. In this Perspective, we examine recent progress in elucidating and articulating the role halide ions play in seeded growth with particular emphasis on gold nanoparticles.

Twisting nanoparticles: Plasmonic circular dichroism was experimentally obtained in chiral 3D organizations of gold nanorods obtained by self-assembly of the nanoantennas onto a fiber template with a twisted morphology. Numerical simulations based on coupled dipoles confirm the crucial role of gold nanorods in this intense circular dichroism.

Silver nanoparticles prepared through a borohydride-reduction method were directly coated with silica by means of a seeded polymerization technique based on the Stober method. Various amine catalysts were used for initialization of a sol-gel reaction of TEOS with no need for a prior surface modification. Use of dimethylamine (DMA) as a catalyst was found to be necessary to obtain a proper coating. The silica shell thickness was varied from 28 to 76 nm for TEOS concentrations of 1-15 mM at 11.1 M water and 0.8 M DMA. The optical spectra of the core-shell silver-silica composite particles show a qualitative agreement with predictions by Mie theory.

We show here that thermal treatment of small seeds results in extensive twinning and a subsequent drastic yield improvement (>85%) in the formation of pentatwinned nanoparticles, with pre-selected morphology (nanorods, bipyramids and decahedra) and aspect ratio.The "quality" of the seeds thus defines the yield of the obtained nanoparticles, which in the case of nanorods avoids the need for additives such as Ag+ ions.This modified seeded growth method also improves reproducibility, as the seeds can be stored for extended periods of time without compromising the quality of the final nanoparticles.Additionally, minor modification of the seeds with Pd allows their localization within the final particles, which opens new avenues toward mechanistic studies.All together, these results represent a paradigm shift in anisotropic gold nanoparticle synthesis.

ConspectusThe primary function of the cell membrane is to protect cells from their surroundings. This entails a strict regulation on controlling the exchange of matter between the cell and its environment. A key factor when considering potential biological applications of a particular chemical structure has to do with its ability to internalize into cells. Molecules that can readily cross cell membranes are frequently needed in biological research and medicine, since most therapeutic entities are designed to modulate intracellular components. However, the design of molecules that do not penetrate cells is also relevant toward, for example, extracellular contrast agents, which are most widely used in clinical diagnosis.Small molecules have occupied the forefront of biomedical research until recently, but the past few decades have seen an increasing use of larger chemical structures, such as proteins or nanoparticles, leading to unprecedented and often unexpectedly novel research. Great achievements have been made toward understanding the rules that govern cellular uptake, which show that cell internalization of molecules is largely affected by their size. For example, macromolecules such as proteins and nucleic acids are usually unable to internalize cells. Intriguingly, in the case of nanoparticles, larger sizes seem to facilitate internalization via endocytic pathways, through which the particles remain trapped in lysosomes and endosomes.In this Account, we aimed at presenting our personal view of how different chemical structures behave in terms of cell internalization due to their size, ranging from small drugs to large nanoparticles. We first introduce the properties of cell membranes and the main mechanisms involved in cellular uptake. We then discuss the cellular internalization of molecules, distinguishing between those with molecular weights below 1 kDa and biological macromolecules such as proteins and nucleic acids. In the last section, we review the biological behavior of nanoparticles, with a special emphasis on plasmonic nanoparticles, which feature a high potential in the biomedical field. For each group of chemical structures, we discuss the parameters affecting their cellular internalization but also strategies that can be applied to achieve the desired intracellular delivery. Particular attention is paid to approaches that allow conditional regulation of the cell internalization process using external triggers, such as activable cell penetrating peptides, due to the impact that these systems may have in drug delivery and sensing applications. The Account ends with a “Conclusions and Outlook” section, where general lessons and future directions toward further advancements are briefly presented.

Visible and near-infrared optical excitations are common currency in the biological world, and consequently, they are routinely used to investigate microscopic phenomena taking place in living organisms and their environment. However, the wavelength of light within that energy region is above hundreds of nanometers, thus averting the possibility of direct nanometer-scale resolution. We show in this Perspective that narrow gaps between metals and sharp tips in colloidal gold particles constitute excellent “light confiners” that permit solving this problem, and in particular, they lead to record levels of surface-enhanced Raman scattering. Our results are framed in the context of a historical quest toward achieving optical focusing in the near field, and we offer a tutorial explanation of why evanescent waves such as plasmons are needed for deep-subwavelength focusing. These results provide the required elements of intuition to understand light concentration at the nanometer scale and to design optimized systems for application in ultrasensitive optical analyses and nonlinear photonics.

It is widely accepted that the physical properties of nanostructures depend on the type of surface facets. For Au nanorods, the surface facets have a major influence on crucial effects such as reactivity and ligand adsorption and there has been controversy regarding facet indexing. Aberration-corrected electron microscopy is the ideal technique to study the atomic structure of nanomaterials. However, these images correspond to two-dimensional (2D) projections of 3D nano-objects, leading to an incomplete characterization. Recently, much progress was achieved in the field of atomic-resolution electron tomography, but it is still far from being a routinely used technique. Here we propose a methodology to measure the 3D atomic structure of free-standing nanoparticles, which we apply to characterize the surface facets of Au nanorods. This methodology is applicable to a broad range of nanocrystals, leading to unique insights concerning the connection between the structure and properties of nanostructures.

The response of gold nanorods to both thermal and ultrafast laser-induced heating has been examined. The thermal heating experiments show structural changes that occur on timescales ranging from hours to days. At the highest temperature examined (250 °C) the nanorods are transformed into spheres within an hour. On the other hand, no structural changes are observed in the laser-induced heating experiments up to temperatures of 700 ± 50 °C. This is attributed to thermal diffusion in the laser experiments. Measurements of the period of the extensional mode of the nanorods using time-resolved spectroscopy show a significant softening at high pump laser powers. However, the decrease in the period is less than expected from bulk Young's modulus vs. temperature data.

Caught in a trap: Colloids of gold nanoparticles coated with a thermally responsive poly-(N-isopropylacrylamide) (pNIPAM) microgel can trap molecules in different ways as a function of temperature (see scheme). The porous pNIPAM shells prevent electromagnetic coupling between metal particles, thus providing highly reproducible surface-enhanced Raman scattering (SERS) signals and intensity. 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.

A detailed study is presented of <italic>in vivo</italic> protein corona formation on anisotropic gold nanoparticles, after blood circulation in mice.

In this tutorial review, we provide an overview of the recent research toward surface functionalization of plasmonic nanoparticles for the generation of advanced optical sensors that make possible the analysis of various moieties by means of surface enhanced Raman scattering (SERS). Such moieties include atomic ions, low affinity target molecules, inorganic anions, biometabolites, pathogen markers and/or other analytes of interest even under very demanding circumstances such as those related to real life samples. We expect this review to be of interest to researchers in a broad diversity of fields that can take advantage of the unprecedented sensitivity of this type of molecular spectroscopy, in a wide variety of analytical and bioanalytical problems.

Recent reports have illustrated the promising potential of chiral metal nanostructures, which exploit the characteristic localized surface plasmon resonance of metal colloids, to produce intense optical activity. In this article we review the concepts, synthetic methods, and theoretical predictions underlying the chirality of metal colloids with a particular emphasis on the size range of 10–100 nanometers. The formation of individual colloidal nanoparticles with a chiral morphology and a plasmonic response remains elusive; however, collective chirality and the associated optical activity in nanoparticle assemblies is a promising alternative that has seen a few recent experimental demonstrations. We conclude with a perspective on chiral nanostructures built up from achiral anisotropic metal particles.

Materials scientists have performed exceptional accomplishments in the design of various types of materials that can be directly used for biomedical research. In particular, nanomaterials (including plasmonic nanoparticles) have become forefront scaffolds for designing bioactive materials. The application of such materials in biomedicine however requires a directed design providing actuation and stability in a particularly complex environment such as living organisms. Enhanced diagnostic tools for diseases such as cancer and HIV are pursued, and in this context nanoparticles offer exclusive physicochemical features for accurate biosensing, as well as actuation. We discuss the biosensing capabilities of plasmonic nanoparticles, in connection with SERS imaging. Novel therapies based on local drug delivery and photothermal therapy activated by nanoparticles are being explored. These applications are briefly discussed in this article, considering the actual biological problems faced by materials scientists and highlighting the beneficial interactions between materials science and biomedicine, which lead to novel routes in biomedical research and practice.

Surface enhanced Raman scattering (SERS) spectroscopy is a powerful technique that provides molecular information through greatly enhanced Raman scattering from minute amounts of substance near nanostructured metallic surfaces. SERS is thus a promising technique for ultrasensitive sensing applications. Plasmonic nanostructures including metal nanoparticles and lithographically prepared nanostructures are ideal substrates to produce enhanced Raman signals. Numerous studies have been published on the production of SERS-active substrates for SERS measurements including solution phase methods and solid supports. In SERS applications, hot spots where the electromagnetic field is particularly intense, play a key role. In this review, we provide an overview of techniques designed for the creation of SERS hot spots both in solution and on solid supports. We first introduce the self-assembly of spherical and anisotropic nanoparticles in solution, to then focus on a wide variety of techniques to assemble nanoparticles onto solid supports. We also describe top-down approaches typically based on lithography techniques. Finally, we provide our own view on the current state of the field and the aspects where further development is expected.

Surface-enhanced Raman scattering (SERS) is one of the most straightforward applications of the so-called nanoplasmonics. This powerful molecular spectroscopy technique is based on the enhancement of the inelastic scattering from molecules located near nanostructured metallic surfaces when these are illuminated and surface plasmons are excited. The analytical applications of SERS are hindered when the Raman cross-section of the analyte is too low, which is often the case in inorganic molecular species. This problem is even more serious when atomic species are to be identified, since these cannot display a vibrational signal. Herein we discuss the recent advancements toward the SERS detection of small inorganic compounds, including both molecular and atomic species.

Coupling of localized surface plasmon resonances results in singular effects at the void space between noble metal nanoparticles. However, implementation of practical applications based on plasmon coupling calls for the high yield production of metal nanoparticle clusters (dimers, trimers, tetramers,…) with small gaps. Therefore, controlled assembly using colloid chemistry methods is an emerging and promising field. We present a brief overview over the controlled assembly of plasmonic nanoparticle clusters by colloid chemistry methods, together with a description of their plasmonic properties and some applications, with an emphasis in sensing through surface-enhanced Raman scattering spectroscopy for bio-detection purposes. We point out the important role of separation methods to obtain colloidal clusters in high yield. A special encouragement to explore assembly of anisotropic building blocks is pursued.

Gold nanoparticles are encapsulatedwithin thermoresponsive pNIPAMmigrogels through an easy two-stepprotocol. The core/shell structure ofthe composite is characterized by TEM,AFM, PCS, and UV-vis spectroscopy. The restricted environment and thehigh porosity of the microgel shell arestudied through the overgrowth of thegold core. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2008/adma200800064_s.pdf or from the author. 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.

Metal colloids are of great interest in the field of nanophotonics, mainly due to their morphology-dependent optical properties, but also because they are high-quality building blocks for complex plasmonic architectures. Close-packed colloidal supercrystals not only serve for investigating the rich plasmonic resonances arising in strongly coupled arrangements but also enable tailoring the optical response, on both the nano- and the macroscale. Bridging these vastly different length scales at reasonable fabrication costs has remained fundamentally challenging, but is essential for applications in sensing, photovoltaics or optoelectronics, among other fields. We present here a scalable approach to engineer plasmonic supercrystal arrays, based on the template-assisted assembly of gold nanospheres with topographically patterned polydimethylsiloxane molds. Regular square arrays of hexagonally packed supercrystals were achieved, reaching periodicities down to 400 nm and feature sizes around 200 nm, over areas up to 0.5 cm2. These two-dimensional supercrystals exhibit well-defined collective plasmon modes that can be tuned from the visible through the near-infrared by simple variation of the lattice parameter. We present electromagnetic modeling of the physical origin of the underlying hybrid modes and demonstrate the application of superlattice arrays as surface-enhanced Raman scattering (SERS) spectroscopy substrates which can be tailored for a specific probe laser. We therefore investigated the influence of the lattice parameter, local degree of order, and cluster architecture to identify the optimal configuration for highly efficient SERS of a nonresonant Raman probe with 785 nm excitation.

Plasmonic nanostructures have played a significant role in the field of nanotechnology due to their unprecedented ability to concentrate light at the nanometre scale, which renders them precious for various sensing applications. The adsorption of plasmonic nanoparticles and nanostructures onto solid substrates in a controlled manner is a crucial process for the fabrication of nanoplasmonic devices, in which the nanoparticles amplify the electromagnetic fields for enhanced device performance. In this perspective article we summarize recent developments in the fabrication of flexible nanoplasmonic devices for sensing applications based on surface enhanced Raman scattering (SERS) and localized surface plasmon resonance (LSPR) shifts. We introduce different types of flexible substrates such as filter paper, free-standing nanofibres, elastomers, plastics, carbon nanotubes and graphene, for the fabrication of low-cost flexible nanoplasmonic devices. Various techniques are described that allow impregnation of such flexible substrates with plasmonic nanoparticles, including solution processes, physical vapour deposition and lithographic techniques. From the discussion in this Perspective, it is clear that highly sensitive and reproducible flexible plasmonic devices can currently be fabricated on a large scale at relatively low-cost, toward real-world applications in diagnostics and detection.

Nanoplasmonics is a rapidly growing field of research that opens up multiple opportunities toward practical applications. The understanding of the extreme confinement of light at the nanoscale has facilitated the development of a wide range of interesting materials for many different fields. Nanoparticles of noble metals, such as gold or silver, present unique optical properties that may end up making a large impact on our daily lives. Modern biomedical techniques can successfully treat cancer via plasmon‐mediated photothermal therapy, in which metal nanoprobes act as intense heaters to kill cancer cells. Moreover, our society is also seeing an increasing interest in the development of alternative (green) energy sources, where plasmonic nanostructures are also considered to provide an advantage, e.g., improving the performance and feasibility of photovoltaic devices. In this progress report, relevant advances and applications of plasmonic nanoparticles, from energy to health, are discussed, and their potential implications in future society are highlighted.

Colloidal nanoparticles (NPs) have become versatile building blocks in a wide variety of fields. Here, we discuss the state-of-the-art, current hot topics, and future directions based on the following aspects: narrow size-distribution NPs can exhibit protein-like properties; monodispersity of NPs is not always required; assembled NPs can exhibit collective behavior; NPs can be assembled one by one; there is more to be connected with NPs; NPs can be designed to be smart; surface-modified NPs can directly reach the cytosols of living cells.

Significance This contribution reports on the application of gold nanorods to the detection of amyloids in Parkinson’s and prion diseases. We found that gold nanorods show no interaction with monomeric proteins but adsorb onto helical protein fibrils. Chiral amyloid templates induce helical arrangement of nanorods, giving rise to intense optical activity at the plasmon resonance wavelengths. This report shows the use of protein fibrils as templates for chiral nanoparticle assembly and development of a biodetection technique. We show this effect on a model recombinant protein, α-synuclein (involved in Parkinson’s disease), using CD, cryogenic transmission EM tomography, and theoretical simulations supporting the experimental findings. We additionally show application to identify patients with Parkinson’s disease from human brain homogenates.

We investigate theoretically the optical activity of a dimer of plasmonic nanoantennas, mimicking the geometry of a molecule with two isolated chromophores, a situation commonly described as exciton coupling in organic chemistry. As the scale of the system increases and approaches the wavelength of visible light, a rich variety of effects arise that are unique to the plasmonic case. Scattering of light by the particles, negligible in very small clusters, strongly perturbs, and eventually dominates, the optical activity. Additionally, retardation effects in dimers with an interparticle separation commensurate with the wavelength of the incident light affect the electromagnetic coupling between the particles and lead to an asymmetric circular dichroism spectrum. We identify conditions for efficient interaction and predict remarkably large anisotropy factors.

Nanoparticles are widely used in various fields of science and technology as well as in everyday life. In particular, gold and silver nanoparticles display unique optical properties that render them extremely attractive for various applications. In this review, we focus on the use of noble metal nanoparticles as plasmonic nanosensors with extremely high sensitivity, even reaching single molecule detection. Sensors based on plasmon resonance shifts, as well as the use of surface-enhanced Raman scattering and surface-enhanced fluorescence, will be considered in this work.

Plasmonic nanoparticles made of gold and silver have attracted a great deal of research attention in various fields, such as biosensors, imaging, therapy, nanophotonics, catalysis and light harvesting due to their unique optical and electronic properties. Plasmonic nanoparticle colloids may exhibit strong colours in the visible region due to localized surface plasmon resonances, whereas their aggregates exhibit different linear and nonlinear optical properties. Therefore, a smart design of chemical interactions between analytes and the nanoparticles surface may lead to gradual optical changes, which can be probed by various sensing methods, allowing quantitative analyte detection. A significant amount of research has been carried out toward the development of plasmonic sensors based on analyte-induced aggregation of Au or Ag nanoparticles, and the sensitivity and selectivity of such plasmonic biosensors have been greatly improved over the years. In this feature article, we summarize different design strategies that have been employed to induce the aggregation of plasmonic nanoparticles upon the addition of various analytes such as DNA, proteins, organic molecules and inorganic ions. We introduce various optical assays, such as colorimetry, surface-enhanced Raman scattering, two-photon photoluminescence, dynamic light scattering, hyper-Rayleigh scattering and chiroptical activity. From the discussion, it can be concluded that plasmonic sensors based on nanoparticle aggregation offer simple, highly sensitive and selective detection of various analytes. Finally, we discuss some of the future directions of plasmonic nanosensors toward device integration for practical applications.

ConspectusThe vast majority of the outstanding applications of metal nanoparticles (NPs) developed during the last two decades have arisen from their unique optical properties. Within this context, rational synthesis and assembly of gold NPs have been the main research focus, aiming at the design of nanoplasmonic devices with tailored optical functionalities. The progress made in this field is thus to be ascribed to the understanding of the origin of the interaction between light and such gold nanostructures, the dynamics of which have been thoroughly investigated with significant contributions from short and ultrashort pulse laser technologies.We focus this Account on the potential of pulse lasers to provide new fundamental insights into the electron dynamics involved in the interaction of light with the free conduction electrons of Au NPs, that is, localized surface plasmon resonances (LSPRs). The excitation of LSPRs with a femtosecond pulse laser is followed by thermalization of the Au NP electrons and the subsequent relaxation of the nanocrystal lattice and the surrounding environment, which generally results in surface melting. By contrast, nanosecond irradiation usually induces AuNP fragmentation and uncontrolled melting due to overlapping excitation and relaxation phenomena. These concepts have been exploited toward the preparation of highly monodisperse gold nanospheres via pulse laser irradiation of polyhedral nanocrystal colloids, or in the fabrication of nanostructures with “written-in” optical properties. The applicability of pulsed coherent light has been extended toward the direct synthesis and manipulation of Au NPs. Through ablation of a gold target in a liquid with pulse lasers, spherical Au NPs can be synthesized with no need of stabilizing ligands, which is a great advantage in terms of reducing toxicity, rendering these NPs particularly suitable for medical applications. In addition, femtosecond laser irradiation has been proven a unique tool for the controlled welding of plasmonic gold nanostructures by electromagnetic field enhancement at the hot spots of assembled Au NPs. The combination of such nanostructures with pulse lasers promises significant chemical and biochemical advances, including the structural determination of organic reaction intermediates, the investigation of phase transitions in inorganic nanomaterials at mild reaction conditions, or the efficient photothermal destruction of cancer cells avoiding damage of surrounding tissue.

The optical properties of metal nanoparticles, particularly their localized surface plasmon effects, are well established. These plasmonic nanoparticles can respond to their surroundings or even influence the optical processes (for example, absorption, fluorescence and Raman scattering) of molecules located at their surface. As a result, plasmonic nanoparticles have been developed for multiple purposes, ranging from the detection of chemicals and biological molecules to light-harvesting enhancement in solar cells. By dispersing the nanoparticles in polymers and creating a hybrid material, the robustness, responsiveness and flexibility of the system are enhanced while preserving the intrinsic properties of the nanoparticles. In this Review, we discuss the fabrication and applications of plasmonic polymer nanocomposites, focusing on applications in optical data storage, sensing and imaging and photothermal gels for in vivo therapy. Within the nanocomposites, the nanoporosity of the matrix, the overall mechanical stability and the dispersion of the nanoparticles are important parameters for achieving the best performance. In the future, translation of these materials into commercial products rests on the ability to scale up the production of plasmonic polymer nanocomposites with tailored optical features. A responsive material in the form of a polymer or hydrogel can be combined with a signal transduction element in the form of plasmonic particles, resulting in hybrid plasmonic polymer nanocomposites. In this Review, the fabrication and applications of such nanocomposites are discussed. The applications described focus on optical data storage, sensing and imaging and the use of photothermal gels for in vivo therapy.

The translation of a technology from the laboratory into the real world should meet the demand of economic viability and operational simplicity. Inspired by recent advances in conductive ink pens for electronic devices on paper, we present a “pen‐on‐paper” approach for making surface enhanced Raman scattering (SERS) substrates. Through this approach, no professional training is required to create SERS arrays on paper using an ordinary fountain pen filled with plasmonic inks comprising metal nanoparticles of arbitrary shape and size. We demonstrate the use of plasmonic inks made of gold nanospheres, silver nanospheres and gold nanorods, to write SERS arrays that can be used with various excitation wavelengths. The strong SERS activity of these features allowed us to reach detection limits down to 10 attomoles of dye molecules in a sample volume of 10 μL, depending on the excitation wavelength, dye molecule and type of nanoparticles. Furthermore, such simple substrates were applied to pesticide detection down to 20 ppb. This universal approach offers portable, cost effective fabrication of efficient SERS substrates at the point of care. This approach should bring SERS closer to the real world through ink cartridges to be fixed to a pen to create plasmonic sensors at will.

The immense importance of nanoparticles and growing concerns of environmental impact motivate the exploration of new greener synthetic techniques.

While acting as catalysts, Au NP-loaded paper composites display excellent surface enhanced Raman scattering (SERS) efficiency, allowing the real-time monitoring of chemical reactions.

Abstract Hybrid colloids consisting of noble metal cores and metal oxide shells have been under intense investigation for over two decades and have driven progress in diverse research lines including sensing, medicine, catalysis, and photovoltaics. Consequently, plasmonic core–shell particles have come to play a vital role in a plethora of applications. Here, an overview is provided of recent developments in the design and utilization of the most successful class of such hybrid materials, silica‐coated plasmonic metal nanoparticles. Besides summarizing common simple approaches to silica shell growth, special emphasis is put on advanced synthesis routes that either overcome typical limitations of classical methods, such as stability issues and undefined silica porosity, or grant access to particularly sophisticated nanostructures. Hereby, a description is given, how different types of silica can be used to provide noble metal particles with specific functionalities. Finally, applications of such nanocomposites in ultrasensitive analyte detection, theranostics, catalysts, and thin‐film solar cells are reviewed.

Development of novel surface-enhanced Raman scattering (SERS) substrates and how they interface target analytes plays a pivotal role in determining the spectrum profile and SERS enhancement magnitude, as well as their applications. We present here the seed-mediated growth of reduced graphene oxide-gold nanostar (rGO-NS) nanocomposites and employ them as active SERS materials for anticancer drug (doxorubicin, DOX) loading and release. By this synthetic approach, both the morphology of rGO-NS nanohybrids and the corresponding optical properties can be precisely controlled, with no need of surfactant or polymer stabilizers. The developed rGO-NS nanohybrids show tunable optical properties by simply changing growth reaction parameters, improved stability as compared to bare Au nanostars, and sensitive SERS response toward aromatic organic molecules. Furthermore, SERS applications of rGO-NS to probe DOX loading and pH-dependent release are successfully demonstrated, showing promising potential for drug delivery and chemotherapy.

Janus Au–Fe₃O₄ star-sphere nanoparticles show their high versatility as contrast agents in multimodal imaging.

We experimentally and theoretically investigate the interactions between localized plasmons in gold nanorods and excitons in J-aggregates under ambient conditions. Thanks to our sample preparation procedure we are able to track a clear anticrossing behavior of the hybridized modes not only in the extinction but also in the photoluminescence (PL) spectra of this hybrid system. Notably, while previous studies often found the PL signal to be dominated by a single mode (emission from so-called lower polariton branch), here we follow the evolution of the two PL peaks as the plasmon energy is detuned from the excitonic resonance. Both the extinction and PL results are in good agreement with the theoretical predictions obtained for a model that assumes two interacting modes with a ratio between the coupling strength and the plasmonic losses close to 0.4, indicative of the strong coupling regime with a significant Rabi splitting estimated to be ∼200 meV. The evolution of the PL line shape as the plasmon is detuned depends on the illumination wavelength, which we attribute to an incoherent excitation given by decay processes in either the metallic rods or the J-aggregates.

Analytical expressions are applied to calculate the plasmonic spectra of nanoparticles with arbitrary morphology, in excellent agreement with experimental data.

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.

Molybdenum disulfide (MoS2), a promising two-dimensional transition-metal dichalcogenide, presents a challenge in the tuning of its optoelectronic and chemical properties. Herein, we demonstrate an efficient route to alter the crystalline structure of MoS2 by chemical exfoliation. Using NaK metal alloys, exfoliated and covalently functionalized MoS2 derivatives were obtained with a high metallic (1T) phase ratio, up to 94.5%. Consequently, exfoliated MoS2 showed a significant surface-enhanced Raman scattering activity toward rhodamine 6G (R6G) and crystal violet, with low detection limits. The versatility of this approach allows the covalent functionalization of MoS2 without relying on edge or basal-plane defects of the structure and preserving the high-ratio 1T phase.

We have recently witnessed a major improvement in the quality of nanoparticles encoded with Raman-active molecules (SERS tags). Such progress relied mainly on a major improvement of fabrication methods for building-blocks, resulting in widespread application of this powerful tool in various fields, with the potential to replace commonly used techniques, such as those based on fluorescence. We present hereby a brief Perspective on surface enhanced Raman scattering (SERS) tags, regarding their composition, morphology, and structure, and describe our own selection from the current state-of-the-art. We then focus on the main bioimaging applications of SERS tags, showing a gradual evolution from two-dimensional studies to three-dimensional analysis. Recent improvements in sensitivity and multiplexing ability have enabled great advancements toward in vivo applications, e.g., highlighting tumor boundaries to guide surgery. In addition, the high level of biomolecule sensitivity reached by SERS tags promises an expansion toward biomarker detection in cases for which traditional methods offer limited reliability, as a consequence of the frequently low analyte concentrations.

Synthetic methods allow the growth of metal nanoparticles with intrinsic chiral morphology and plasmonic optical activity in the visible and near-IR.

Future precision medicine will be undoubtedly sustained by the detection of validated biomarkers that enable a precise classification of patients based on their predicted disease risk, prognosis, and response to a specific treatment. Up to now, genomics, transcriptomics, and immunohistochemistry have been the main clinically amenable tools at hand for identifying key diagnostic, prognostic, and predictive biomarkers. However, other molecular strategies, including metabolomics, are still in their infancy and require the development of new biomarker detection technologies, toward routine implementation into clinical diagnosis. In this context, surface-enhanced Raman scattering (SERS) spectroscopy has been recognized as a promising technology for clinical monitoring thanks to its high sensitivity and label-free operation, which should help accelerate the discovery of biomarkers and their corresponding screening in a simpler, faster, and less-expensive manner. Many studies have demonstrated the excellent performance of SERS in biomedical applications. However, such studies have also revealed several variables that should be considered for accurate SERS monitoring, in particular, when the signal is collected from biological sources (tissues, cells or biofluids). This Perspective is aimed at piecing together the puzzle of SERS in biomarker monitoring, with a view on future challenges and implications. We address the most relevant requirements of plasmonic substrates for biomedical applications, as well as the implementation of tools from artificial intelligence or biotechnology to guide the development of highly versatile sensors.

From small molecules to entire organisms, evolution has refined biological structures at the nanoscale, microscale and macroscale to be chiral—that is, mirror dissymmetric. Chirality results in biological, chemical and physical properties that can be influenced by circularly polarized electromagnetic fields. Chiral nanoscale materials can be designed that mimic, refine and advance biological chiral geometries, to engineer optical, physical and chemical properties for applications in photonics, sensing, catalysis and biomedicine. In this Review, we discuss the mechanisms underlying chirality transfer in nature and provide design principles for chiral nanomaterials. We highlight how chiral features emerge in inorganic materials during the chemical synthesis of chiral nanostructures, and outline key applications for inorganic chiral nanomaterials, including promising designs for biomedical applications, such as biosensing and immunomodulation. We conclude with an outlook to future opportunities and challenges, including the need for refined characterization techniques. Chiral inorganic nanomaterials can induce specific physical, chemical and biological phenomena. This Review discusses how chiral biomolecules and polarized light allow nanoscale chirality control in inorganic nanomaterials, which can be applied in optical devices, sensing, catalysis and biomedicine.

With the total amount of worldwide data skyrocketing, the global data storage demand is predicted to grow to 1.75 × 1014 GB by 2025. Traditional storage methods have difficulties keeping pace given that current storage media have a maximum density of 103 GB/mm3. As such, data production will far exceed the capacity of currently available storage methods. The costs of maintaining and transferring data, as well as the limited lifespans and significant data losses associated with current technologies also demand advanced solutions for information storage. Nature offers a powerful alternative through the storage of information that defines living organisms in unique orders of four bases (A, T, C, G) located in molecules called deoxyribonucleic acid (DNA). DNA molecules as information carriers have many advantages over traditional storage media. Their high storage density, potentially low maintenance cost, ease of synthesis, and chemical modification make them an ideal alternative for information storage. To this end, rapid progress has been made over the past decade by exploiting user-defined DNA materials to encode information. In this review, we discuss the most recent advances of DNA-based data storage with a major focus on the challenges that remain in this promising field, including the current intrinsic low speed in data writing and reading and the high cost per byte stored. Alternatively, data storage relying on DNA nanostructures (as opposed to DNA sequence) as well as on other combinations of nanomaterials and biomolecules are proposed with promising technological and economic advantages. In summarizing the advances that have been made and underlining the challenges that remain, we provide a roadmap for the ongoing research in this rapidly growing field, which will enable the development of technological solutions to the global demand for superior storage methodologies.

The acquisition of strong chiroptical activity has revolutionized the field of plasmonics, granting access to novel light-matter interactions and revitalizing research on both the synthesis and application of nanostructures. Among the different mechanisms for the origin of chiroptical properties in colloidal plasmonic systems, the self-assembly of achiral nanoparticles into optically active materials offers a versatile route to control the structure-optical activity relationships of nanostructures, while simplifying the engineering of their chiral geometries. Such unconventional materials include helical structures with a precisely defined morphology, as well as large scale, deformable substrates that can leverage the potential of periodic patterns. Some promising templates with helical structural motifs like liquid crystal phases or confined block co-polymers still need efficient strategies to direct preferential handedness, whereas other templates such as silica nanohelices can be grown in an enantiomeric form. Both types of chiral structures are reviewed herein as platforms for chiral sensing: patterned substrates can readily incorporate analytes, while helical assemblies can form around structures of interest, like amyloid protein aggregates. Looking ahead, current knowledge and precedents point toward the incorporation of semiconductor emitters into plasmonic systems with chiral effects, which can lead to plasmonic-excitonic effects and the generation of circularly polarized photoluminescence.

A robust and reproducible methodology to prepare stable inorganic nanoparticles with chiral morphology may hold the key to the practical utilization of these materials. An optimized chiral growth method to prepare fourfold twisted gold nanorods is described herein, where the amino acid cysteine is used as a dissymmetry inducer. Four tilted ridges are found to develop on the surface of single-crystal nanorods upon repeated reduction of HAuCl4 , in the presence of cysteine as the chiral inducer and ascorbic acid as a reducing agent. From detailed electron microscopy analysis of the crystallographic structures, it is proposed that the dissymmetry results from the development of chiral facets in the form of protrusions (tilted ridges) on the initial nanorods, eventually leading to a twisted shape. The role of cysteine is attributed to assisting enantioselective facet evolution, which is supported by density functional theory simulations of the surface energies, modified upon adsorption of the chiral molecule. The development of R-type and S-type chiral structures (small facets, terraces, or kinks) would thus be non-equal, removing the mirror symmetry of the Au NR and in turn resulting in a markedly chiral morphology with high plasmonic optical activity.

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTBest Practices for Using AI When Writing Scientific ManuscriptsCaution, Care, and Consideration: Creative Science Depends on ItJillian M. Buriak*Jillian M. Buriak*Email: [email protected]More by Jillian M. Buriakhttps://orcid.org/0000-0002-9567-4328, Deji AkinwandeDeji AkinwandeMore by Deji Akinwandehttps://orcid.org/0000-0001-7133-5586, Natalie ArtziNatalie ArtziMore by Natalie Artzihttps://orcid.org/0000-0002-2211-6069, C. Jeffrey BrinkerC. Jeffrey BrinkerMore by C. Jeffrey Brinkerhttps://orcid.org/0000-0002-7145-9324, Cynthia BurrowsCynthia BurrowsMore by Cynthia Burrowshttps://orcid.org/0000-0001-7253-8529, Warren C. W. ChanWarren C. W. ChanMore by Warren C. W. Chanhttps://orcid.org/0000-0001-5435-4785, Chunying ChenChunying ChenMore by Chunying Chenhttps://orcid.org/0000-0002-6027-0315, Xiaodong ChenXiaodong ChenMore by Xiaodong Chenhttps://orcid.org/0000-0002-3312-1664, Manish ChhowallaManish ChhowallaMore by Manish Chhowallahttps://orcid.org/0000-0002-8183-4044, Lifeng ChiLifeng ChiMore by Lifeng Chihttps://orcid.org/0000-0003-3835-2776, William ChuehWilliam ChuehMore by William Chuehhttps://orcid.org/0000-0002-7066-3470, Cathleen M. CruddenCathleen M. CruddenMore by Cathleen M. Cruddenhttps://orcid.org/0000-0003-2154-8107, Dino Di CarloDino Di CarloMore by Dino Di Carlohttps://orcid.org/0000-0003-3942-4284, Sharon C. GlotzerSharon C. GlotzerMore by Sharon C. Glotzerhttps://orcid.org/0000-0002-7197-0085, Mark C. HersamMark C. HersamMore by Mark C. Hersamhttps://orcid.org/0000-0003-4120-1426, Dean HoDean HoMore by Dean Hohttps://orcid.org/0000-0002-7337-296X, Tony Y. HuTony Y. HuMore by Tony Y. Huhttps://orcid.org/0000-0002-5166-4937, Jiaxing HuangJiaxing HuangMore by Jiaxing Huanghttps://orcid.org/0000-0001-9176-8901, Ali JaveyAli JaveyMore by Ali Javeyhttps://orcid.org/0000-0001-7214-7931, Prashant V. KamatPrashant V. KamatMore by Prashant V. Kamathttps://orcid.org/0000-0002-2465-6819, Il-Doo KimIl-Doo KimMore by Il-Doo Kimhttps://orcid.org/0000-0002-9970-2218, Nicholas A. KotovNicholas A. KotovMore by Nicholas A. Kotovhttps://orcid.org/0000-0002-6864-5804, T. Randall LeeT. Randall LeeMore by T. Randall Leehttps://orcid.org/0000-0001-9584-8861, Young Hee LeeYoung Hee LeeMore by Young Hee Leehttps://orcid.org/0000-0001-7403-8157, Yan LiYan LiMore by Yan Lihttps://orcid.org/0000-0002-3828-8340, Luis M. Liz-MarzánLuis M. Liz-MarzánMore by Luis M. Liz-Marzánhttps://orcid.org/0000-0002-6647-1353, Paul MulvaneyPaul MulvaneyMore by Paul Mulvaneyhttps://orcid.org/0000-0002-8007-3247, Prineha NarangPrineha NarangMore by Prineha Naranghttps://orcid.org/0000-0003-3956-4594, Peter NordlanderPeter NordlanderMore by Peter Nordlanderhttps://orcid.org/0000-0002-1633-2937, Rahmi OkluRahmi OkluMore by Rahmi Okluhttps://orcid.org/0000-0003-4984-1778, Wolfgang J. ParakWolfgang J. ParakMore by Wolfgang J. Parakhttps://orcid.org/0000-0003-1672-6650, Andrey L. RogachAndrey L. RogachMore by Andrey L. Rogachhttps://orcid.org/0000-0002-8263-8141, Mathieu SalanneMathieu SalanneMore by Mathieu Salannehttps://orcid.org/0000-0002-1753-491X, Paolo SamorìPaolo SamorìMore by Paolo Samorìhttps://orcid.org/0000-0001-6256-8281, Raymond E. SchaakRaymond E. SchaakMore by Raymond E. Schaakhttps://orcid.org/0000-0002-7468-8181, Kirk S. SchanzeKirk S. SchanzeMore by Kirk S. Schanzehttps://orcid.org/0000-0003-3342-4080, Tsuyoshi SekitaniTsuyoshi SekitaniMore by Tsuyoshi Sekitanihttps://orcid.org/0000-0003-1070-2738, Sara SkrabalakSara SkrabalakMore by Sara Skrabalakhttps://orcid.org/0000-0002-1873-100X, Ajay K. SoodAjay K. SoodMore by Ajay K. Soodhttps://orcid.org/0000-0002-4157-361X, Ilja K. VoetsIlja K. VoetsMore by Ilja K. Voetshttps://orcid.org/0000-0003-3543-4821, Shu WangShu WangMore by Shu Wanghttps://orcid.org/0000-0001-8781-2535, Shutao WangShutao WangMore by Shutao Wanghttps://orcid.org/0000-0002-2559-5181, Andrew T. S. WeeAndrew T. S. WeeMore by Andrew T. S. Weehttps://orcid.org/0000-0002-5828-4312, and Jinhua YeJinhua YeMore by Jinhua Yehttps://orcid.org/0000-0002-8105-8903Cite this: ACS Nano 2023, 17, 5, 4091–4093Publication Date (Web):February 27, 2023Publication History Published online27 February 2023Published inissue 14 March 2023https://doi.org/10.1021/acsnano.3c01544Copyright © 2023 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views102732Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. 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The pseudo-two-dimensional (2D) morphology of plate-like metal nanoparticles makes them one of the most anisotropic, mechanistically understood, and tunable structures available. Although well-known for their superior plasmonic properties, recent progress in the 2D growth of various other materials has led to an increasingly diverse family of plate-like metal nanoparticles, giving rise to numerous appealing properties and applications. In this review, we summarize recent progress on the solution-phase growth of colloidal plate-like metal nanoparticles, including plasmonic and other metals, with an emphasis on mechanistic insights for different synthetic strategies, the crystallographic habits of different metals, and the use of nanoplates as scaffolds for the synthesis of other derivative structures. We additionally highlight representative self-assembly techniques and provide a brief overview on the attractive properties and unique versatility benefiting from the 2D morphology. Finally, we share our opinions on the existing challenges and future perspectives for plate-like metal nanomaterials.

Silver nanoparticles coated with a uniform, thin shell of titanium dioxide are synthesized via a remarkably simple one-pot route, where the reduction of Ag+ to Ag0 and the controlled polymerization of TiO2 on the surface of silver crystallites take place simultaneously. The prepared dispersions of coated nanoparticles display a surface plasmon band, which is significantly red-shifted with respect to that of bare Ag. High-quality ultrathin films of the core−shell clusters are prepared via layer-by-layer assembly. The nanoparticles are arranged in closely packed layers interlaced with polyelectrolyte producing a stratified core−shell hybrid material with unique structure and catalytic and electron-transport properties.

Nanometre-sized CdS semiconductor particles were synthesized in the presence of sodium citrate, and subsequently surrounded by a homogeneous silica shell. The coating procedure makes use of 3-(mercaptopropyl) trimethoxy silane (MPS) as a surface primer to deposit a thin silica shell in water. The dispersion is then transferred into ethanol, where thicker shells can be grown. The citrate-stabilized particles are slowly degraded through photochemical oxidation in the presence of dissolved oxygen. This destabilizing process is suppressed when a homogeneous, microporous silica shell is built up around the particles, through a limited access of O2 molecules to the CdS surface.

Core–shell and multishell bimetallic AuAg nanoparticles have been synthesized by successive reduction of metal salts with ascorbic acid on pre-made seeds in the presence of a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The coverage of the seeds is extremely uniform, although in some cases deviations from a spherical shape are observed with the formation of nanorods or nanoprisms. The evolution of the optical properties as further metal layers are deposited is very dramatic and can be modelled using Mie theory for multilayer spheres. However, preliminary results using high-resolution STEM-XEDS elemental mapping suggest that the actual distribution of the two metals within the multilayer spheres may involve (partial) alloying of the metals.

The formation of nanostructured materials through the assembly of nanocrystals is described, focusing in particular on silica and other metal oxide coated core particles. The preparation and optical characterization of core−shell materials are reviewed, and some of the unique properties of core−shell materials are presented. Shell layers are shown to serve various functions. They may increase colloid stability, aid dispersion in various media, alter the optical and electrical properties of the core, add robustness, or provide a contiguous framework from which inverse lattices may be generated. The assembly of the particles into well-defined thin films and two-dimensional and three-dimensional crystals is discussed, and the resultant optical properties are reviewed. Approaches to increase the topological complexity are studied, and the potential for the creation of a variety of space-filling nanostructures (such as inverse lattices, opals, and photonic crystals) is illustrated.

The synthesis of monodispersed, amorphous cobalt nanoparticles coated with silica in aqueous/ethanolic solution is described. Both the core size and the silica shell thickness can be controlled through the synthetic conditions. Furthermore, the transformation of the cobalt cores into crystalline, metallic cobalt upon annealing in air is demonstrated through X-ray diffraction data. Both the initial, amorphous nanoparticles and their crystalline counterpart are magnetic, which promises important applications for ferrofluid preparation and for magnetic recording media.

CdSe and CdSe@CdS semiconductor nanocrystals have been synthesized in aqueous solutions, using sodium citrate as a stabilizer. Although initially these quantum dots display photoluminescence with very low quantum yields, upon prolonged illumination with visible light, enhancements up to 5000% have been measured. This leads to aqueous quantum dots with high luminescence, which can have important implications in biological and other applications. A distinct correlation between the photocorrosion process and the photoactivation process is observed. The primary reason for luminescence enhancement is considered to be the smoothing of the CdSe core surface. Importantly, even stronger activation was observed in silica- and CdS-coated nanocolloids where the CdSe core was expected to be shielded from photocorrosion. Preferential adsorption of oxygen molecules in the porous silicate shell accelerates the photocorrosion process. In CdS-coated particles, incomplete coating of the original particles is postulated, which is accompanied by the reforming of the CdS coat because of ionic diffusion at the interface on the newly opening areas with smoother surfaces.

Advances in nanophotonics have shown the potential of colloidal metal particles with sharp tips, such as nanostars, to focalize the plasmonic electromagnetic fields. We describe in this paper the performance of gold nanostars in common surface-enhanced scattering (SES) experiments, including SERS, SERRS, and SEF. The study was carried out for several analytes and demonstrated the potential of nanostars for ultradetection of nonfunctionalized analytes, by simply depositing nanostars on top of analyte thin films previously assembled onto a smooth gold surface.

A super lattice: The title system allows the spontaneous formation of self-assembled 2D and 3D highly ordered aggregates of standing nanorods on large superlattice domains (see picture). The hexagonal close packing of nanorods perpendicular to the substrate resembles smectic-B liquid-crystalline phases. Optical characterization of the aggregates demonstrates their anisotropic optical response. 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.

Thiol-modified poly(ethylene glycol) (mPEG-SH) has been used to replace standard capping agents from the surfaces of gold nanoparticles with different sizes and shapes. Upon PEG stabilization, the nanoparticles can be transferred into ethanol, where silica can be directly grown on the particle surfaces through the standard Stober process. The obtained silica shells are uniform and homogeneous, and the method allows a high degree of control over shell thickness for any particle size and shape. Additionally, Raman-active molecules can be readily incorporated within the composite nanoparticles during silica growth so that SERS/SERRS-encoded nanoparticles can be fabricated containing a variety of tags, thereby envisaging multiplexing capability.

The optical extinction spectra of single silver nanoparticles coated with a silica shell were investigated in the size range 10−50 nm. Measurements were performed using the spatial modulation spectroscopy technique which permits independent determination of both the size of the metal nanoparticle under study and the width of its localized surface plasmon resonance (LSPR). These parameters can thus be directly correlated at a single particle level for the first time. The results show a linear increase of the width of the LSPR with the inverse diameter in the small size regime (less than 25 nm). For these nanoparticles of well-controlled environment, this can be ascribed to quantum confinement of electrons or, classically, to increase of the electron surface scattering processes. The impact of this effect was measured quantitatively and compared to the predictions by theoretical models.

The use of tetraalkylammonium hydroxides to prepare ZnO colloids with diameters ranging from 1 to 6 nm is described. The position of the first excitonic transition has been measured by UV-vis spectrometry and correlated with the particle size, which has been measured using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and ultracentrifugation (UC). The exciton transition is first visible at 265–270 nm corresponding to particle diameters around 1 nm; the exciton absorption band then becomes sharper and narrower, while the band red-shifts only slowly. Based on the sizing data from HRTEM, XRD, and UC, it is concluded that the quantum size effect at sizes less than the Bohr radius is significantly less than predicted from the Kayanuma equation. Based on the blue-shift in the trap emission as a function of nanocrystal size, the effective masses of the electron and hole (me, mh) remain constant in particles down to 1 nm in diameter, with a relative value given by me/(me+mh)=0.55 ± 0.04.

This review article presents a general view of the recent progress in the fast developing area of surface-enhanced Raman scattering spectroscopy as an analytical tool for the detection and identification of molecular species in very small concentrations, with a particular focus on potential applications in the biomedical area. We start with a brief overview of the relevant concepts related to the choice of plasmonic nanostructures for the design of suitable substrates, their implementation into more complex materials that allow generalization of the method and detection of a wide variety of (bio)molecules and the strategies that can be used for both direct and indirect sensing. In relation to indirect sensing, we devote the final section to a description of SERS-encoded particles, which have found wide application in biomedicine (among other fields), since they are expected to face challenges such as multiplexing and high-throughput screening.

Gold nanoparticles prepared through a conventional citrate-reduction method were directly coated with silica by means of a seeded polymerization technique based on the Stöber method. The method required no surface modification. The addition of tetraethylorthosilicate and water prior to ammonia was found to be critical to obtain a proper coating. The silica shell thickness was varied from 30 to 90 nm for TEOS concentrations of 0.0005-0.02 M at 10.9 M of water and 0.4 M of ammonia. The optical spectra of the core-shell gold-silica composite particles agreed with predictions of Mie theory.

We present a theoretical and experimental study involving the sensing characteristics of wavelength-interrogated plasmonic sensors based on surface plasmon polaritons (SPP) in planar gold films and on localized surface plasmon resonances (LSPR) of single gold nanorods. The tunability of both sensing platforms allowed us to analyze their bulk and surface sensing characteristics as a function of the plasmon resonance position. We demonstrate that a general figure of merit (FOM), which is equivalent in wavelength and energy scales, can be employed to mutually compare both sensing schemes. Most interestingly, this FOM has revealed a spectral region for which the surface sensitivity performance of both sensor types is optimized, which we attribute to the intrinsic dielectric properties of plasmonic materials. Additionally, in good agreement with theoretical predictions, we experimentally demonstrate that, although the SPP sensor offers a much better bulk sensitivity, the LSPR sensor shows an approximately 15% better performance for surface sensitivity measurements when its FOM is optimized. However, optimization of the substrate refractive index and the accessibility of the relevant molecules to the nanoparticles can lead to a total 3-fold improvement of the FOM in LSPR sensors.

Gold nanorods in aqueous solution are generally surrounded by surfactants or capping agents. This is crucial for anisotropic growth during synthesis and for their final stability in solution. When CTAB is used, a bilayer has been evidenced from analytical methods even though no direct morphological characterization of the precise thickness and compactness has been reported. The type of surfactant layer is also relevant to understand the marked difference in further self-assembling properties of gold nanorods as experienced using 16-EO(1)-16 gemini surfactant instead of CTAB. To obtain a direct measure of the thickness of the surfactant layer on gold nanorods synthesized by the seeded growth method, we coupled TEM, SAXS, and SANS experiments for the two different cases, CTAB and gemini 16-EO(1)-16. Despite the strong residual signal from micelles in excess, it can be concluded that the thickness is imposed by the chain length of the surfactant and corresponds to a bilayer with partial interdigitation.

A detailed high-resolution electron microscopy study of the formation of Ag nanowires by solvent reduction in N,N-dimethylformamide (DMF), in the presence of poly(vinylpyrrolidone) (PVP) at high temperature provided clear evidence that the nanowires grow through the oriented aggregation of precursor nanoparticles. The HRTEM images demonstrate that initially, icosahedral and cuboctahedral Ag nanoparticles are formed, which then self-assemble to form aligned stripes, and eventually fuse with each other to yield single crystalline nanowires. The nanoparticle aggregation only takes place through preferred facets of the original nanocrystals, and therefore intermediate twisted wires are observed.

Gold nanoparticles encapsulated in a thermoresponsive microgel (pNIPAM) were used as catalysts in the electron-transfer reaction between hexacyanoferrate(III) and borohydride ions. The thermosensitive pNIPAM network can act as a "nanogate" that can be opened or closed to a certain extent, thereby controlling the diffusion of reactants toward the catalytic core. Interestingly, the crosslinker density plays an important role, because it defines the thermal response of the Au@pNIPAM system and, in turn, the extent of the volume change and therefore the polymeric density. The catalytic activity of the encapsulated gold nanoparticles is thus affected both by temperature and by the composition of the shell. A mathematical model reproducing the key features of the temperature-controlled catalysis by our thermosensitive nanoparticles confirms the effect of diffusion rate through the shell on the actual reaction rate.

Gold nanoparticles are very interesting because of their potential applications in microelectronics, optical devices, analytical detection schemes, and biomedicine. Though shape control has been achieved in several polar solvents, the capability to prepare organosols containing elongated gold nanoparticles has been very limited. In this work we report a novel, simplified method to produce long, thin gold nanowires in an organic solvent (oleylamine), which can be readily redispersed into nonpolar organic solvents. These wires have a characteristic flexible, hairy morphology arising from a small thickness (<2 nm) and an enormous length (up to several micrometers), with the possibility of adjusting the dimensions through modification of the growth conditions, in particular, the gold salt concentration. Despite their extreme aspect ratio, the wires are stable in solution for long periods of time but easily break when irradiated with high-energy electron beams during transmission electron microscopy.

We present a simple, generally applicable procedure for the assembly of nanoparticles on carbon nanotubes in aqueous solution. The method makes use of polyelectrolytes for wrapping carbon nanotubes and providing them with adsorption sites for electrostatically driven nanoparticle deposition. The method is exemplified by the assembly of gold nanoparticles which results in single, optically labelled carbon nanotubes.

Development of multifunctional drug delivery vehicles with therapeutic and imaging capabilities as well as in situ methods of monitoring of intracellular processes will greatly benefit from a simple method of preparation of plasmonic Au structures with nanometer scale gaps between sharp metallic elements where the so-called SERS hot spots can be formed. Here the synthesis of gold lace capsules with average diameters ca. 100 nm made of a network of metallic branches 3-5 nm wide and separated by 1-3 nm gaps is reported. Biocompatible amphiphilic polyurethanes (PUs) were used as template for these particles. The unusual topology of the produced gold lace shells somewhat reminiscent of Fabergé eggs is likely to reflect the network of hydrophobic and hydrophilic domains of PU globules. The gold lace develops from initial open weblike structures by gradual enveloping the PU template. The diameter of gold lace shell is determined by the size of PUs in water and can be adjusted by the molecular mass of PUs. The close proximity between branches makes them excellent supports for surface-enhanced Raman spectroscopy (SERS), which was demonstrated using 1-naphthalenethiol upon excitation with photons with different wavelengths. The loading and releasing of pyrene as a model of hydrophobic drugs and the use of SERS to monitor it were demonstrated.

We present in this review article an overview of the capabilities of surface enhanced Raman scattering (SERS) spectroscopy as a technique for applications related to environmental analysis and monitoring, ranging from the structural characterization of soils, through ultrasensitive detection of pollutants and heavy metal ions, to the analysis of plants, tissues and microorganisms, with a critical approach in which the drawbacks and difficulties associated to the various experimental configurations and enhancing substrates are introduced, as well as perspectives in the different fields.

Single-crystalline Cu nanoplates with a prominent in-plane dipole surface plasmon band are fabricated through reduction of copper salt with hydrazine using PVP as stabilizer and no need for inert atmosphere. Due to the lower free-electron character of copper, the interband transitions overlap, and therefore damp, the out-of-plane dipole plasmon resonance (see image). 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.