Gold nanorods and their plasmonic properties

Localized surface plasmon resonance for enhanced electrocatalysis

Electrocatalysis plays a vital role in energy conversion and storage in modern society. Localized surface plasmon resonance (LSPR) is a highly attractive approach to enhance the electrocatalytic activity and selectivity with solar energy. LSPR excitation can induce the transfer of hot electrons and holes, electromagnetic field enhancement, lattice heating, resonant energy transfer and scattering, in turn boosting a variety of electrocatalytic reactions. Although the LSPR-mediated electrocatalysis has been investigated, the underlying mechanism has not been well explained. Moreover, the efficiency is strongly dependent on the structure and composition of plasmonic metals. In this review, the currently proposed mechanisms for plasmon-mediated electrocatalysis are introduced and the preparation methods to design supported plasmonic nanostructures and related electrodes are summarized. In addition, we focus on the characterization strategies used for verifying and differentiating LSPR mechanisms involved at the electrochemical interface. Following that are highlights of representative examples of direct plasmonic metal-driven and indirect plasmon-enhanced electrocatalytic reactions. Finally, this review concludes with a discussion on the remaining challenges and future opportunities for coupling LSPR with electrocatalysis.

Starch Capped Atomically Thin CuS Nanocrystals for Efficient Photothermal Therapy

Photothermal therapy requires efficient plasmonic nanomaterials with small size, good water dispersibility, and biocompatibility. This work reports a one-pot, 2-min synthesis strategy for ultrathin CuS nanocrystals (NCs) with precisely tunable size and localized surface plasmon resonance (LSPR), where a single-starch-layer coating leads to a high LSPR absorption at the near-IR wavelength 980 nm. The CuS NC diameter increases from 4.7 (1 nm height along [101]) to 28.6 nm (4.9 nm height along [001]) accompanied by LSPR redshift from 978 to 1200 nm, as the precursor ratio decreases from 1 to 0.125. Photothermal temperature increases by 38.6 °C in 50 mg L^-1 CuS NC solution under laser illumination (980 nm, 1.44 W cm^-2 ). Notably, 98.4% of human prostate cancer PC-3/Luc+ cells are killed by as little as 5 mg L^-1 starch-coated CuS NCs with 3-min laser treatment, whereas CuS NCs without starch cause insignificant cell death. LSPR modeling discloses that the starch layer enhances the photothermal effect by significantly increasing the free carrier density and blue-shifting the LSPR toward 980 nm. This study not only presents a new type of photothermally highly efficient ultrathin CuS NCs, but also offers in-depth LSPR modeling investigations useful for other photothermal nanomaterial designs.

Prospects for More Efficient Multi-Photon Absorption Photosensitizers Exhibiting Both Reactive Oxygen Species Generation and Luminescence

The use of two-photon absorption (TPA) for such applications as microscopy, imaging, and photodynamic therapy (PDT) offers several advantages over the usual one-photon excitation. This creates a need for photosensitizers that exhibit both strong two-photon absorption and the highly efficient generation of reactive oxygen species (ROS), as well as, ideally, bright luminescence. This review focuses on different strategies utilized to improve the TPA properties of various multi-photon absorbing species that have the required photophysical properties. Along with well-known families of photosensitizers, including porphyrins, we also describe other promising organic and organometallic structures and more complex systems involving organic and inorganic nanoparticles. We concentrate on the published studies that provide two-photon absorption cross-section values and the singlet oxygen (or other ROS) and luminescence quantum yields, which are crucial for potential use within PDT and diagnostics. We hope that this review will aid in the design and modification of novel TPA photosensitizers, which can help in exploiting the features of nonlinear absorption processes.

Diattenuation and retardance signature of plasmonic gold nanorods in turbid media revealed by Mueller matrix polarimetry

Plasmonic gold nanorods (GNRs) are finding increasing use in biomedicine due to their unique electromagnetic properties, optical contrast enhancement and biocompatibility; they also show promise as polarization contrast agents. However, quantification of their polarization-enhancing properties within heterogeneous turbid media remains challenging. We report on polarization response in controlled tissue phantoms consisting of dielectric microsphere scatterers with varying admixtures of GRNs. Experimental Mueller matrix measurements and polarization sensitive Monte-Carlo simulations show excellent agreement. Despite the GNRs’ 3D random orientation and distribution in the strong multiply scattering background, significant linear diattenuation and retardance were observed. These exclusive measurable characteristics of GNRs suggest their potential uses as contrast enhancers for polarimetric assessment of turbid biological tissue.

A universal route with fine kinetic control to a family of penta-twinned gold nanocrystals

Some of the major difficulties hindering the synthesis of different types of colloidal nanocrystals are their complex synthetic methods and the lack of a universal growth mechanism in one system. Herein, we propose a general strategy of kinetically controlled seed-mediated growth to synthesize a family of penta-twinned gold nanocrystals. Specifically, different kinds of penta-twinned nanocrystals (truncated penta-twinned decahedra, truncated bipyramids, bipyramids, truncated bipyramids with tips, star-like penta-twinned nanocrystals, decahedra with concave edges, and decahedra) with tunable sizes and high purity were readily achieved in one system solely by tailoring the deposition kinetics of adatoms on different sites of decahedral seeds. The controllable deposition kinetics can be realized by changing the ratio of reductant/gold precursors (R), which dictates whether horizontal or vertical features along the 5-fold axis direction of Au decahedral seeds are produced. Additionally, the selective growth of a second metal (silver) on penta-twinned gold seeds can be reached through minor modification of R, which opens a new avenue for mechanistic investigation by visualizing the seed localization within the final particles. The present work demonstrates a general paradigm for the kinetic growth of penta-twinned crystals and would be extended to the synthesis of other families of nanocrystals.

We report the synthesis of linear ADPr oligomers of defined length up to a pentamer using an improved solid phase method. Binding study with human oncogenic helicase ALC1 shows that ADPr oligomers bind to ALC1 in a length-dependent manner.

Functionalized Gold Nanorod Probes: A Sophisticated Design of SERS Immunoassay for Biodetection in Complex Media

Surface-enhanced Raman scattering (SERS) probes offer considerable opportunities in label-based biosensing and analysis. However, achieving specific and reproducible performance, where low detection limits are needed in complex media, remains a challenge. Herein, we present a general strategy employing gold nanorod SERS probes and rationally designed surface chemistry involving protein resistant layers and antibodies to allow for the selective detection of species in complex media. By utilizing the ability of gold nanorods for selective surface modification, Raman reporters (4-mercaptobenzoic acid) were attached to the tips. Importantly, the sides of the nanorods were modified using a mixed layer of two different length stabilizing ligands (carboxyl-terminated oligo ethylene glycols) to ensure colloidal stability, while antibodies were attached to the stabilizing ligands. The nanoparticle interfacial design improves the colloidal stability, unlocks the capability of the probes for targeting biomolecules in complex matrices, and gives the probes the high SERS efficiency. The utility of this probe is demonstrated herein via the detection of Salmonella bacteria at the single bacterium level in complex food matrices using an anti-Salmonella IgG antibody-conjugated probe. The modular nature of the surface chemistry enables the SERS probes to be employed with a molecularly diverse range of biorecognition species (e.g., antibodies and peptides) for many different analytes, thus opening up new opportunities for efficient biosensing applications.

Nanomolding of Gold and Gold-Silicon Heterostructures at Room Temperature

Nanofabrication techniques are limited by at least one of the required characteristics such as choice of material, control over geometry, fabrication requirements, yield, cost, and scalability. Our previously developed method of thermomechanical nanomolding fulfills these requirements, although it requires high processing temperatures. Here, we demonstrate low-temperature molding where we utilize the enhanced diffusivity on "eutectic interfaces". Gold nanorods are molded at room temperature using Au-Si alloy as feedstock. Instead of using alloy feedstock, these "eutectic interfaces" can also be established through a feedstock-mold combination. We demonstrate this by using pure Au as feedstock, which is molded into Si molds at room temperature, and also the reverse, Si feedstock is molded into Au molds forming high aspect ratio Au-Si core-shell nanorods. We discuss the mechanism of this low-temperature nanomolding in terms of lower homologous temperature at the eutectic interface. This technique, based on enhanced eutectic interface diffusion, provides a practical nanofabrication method that eliminates the previous high-temperature requirements, thereby expanding the range of the materials that can be practically nanofabricated.

Dendrimer-modified gold nanorods as a platform for combinational gene therapy and photothermal therapy of tumors

Background

The exploitation of novel nanomaterials combining diagnostic and therapeutic functionalities within one single nanoplatform is challenging for tumor theranostics.

Methods

We synthesized dendrimer-modified gold nanorods for combinational gene therapy and photothermal therapy (PTT) of colon cancer. Poly(amidoamine) dendrimers (PAMAM, G3) grafted gold nanorods were modified with GX1 peptide (a cyclic 7-mer peptide, CGNSNPKSC). The obtained Au NR@PAMAM-GX1 are proposed as a gene delivery vector to gene (FAM172A, regulates the proliferation and apoptosis of colon cancer cells) for the combination of photothermal therapy (PTT) and gene therapy of Colon cancer cells (HCT-8 cells). In addition, the CT imaging function of Au NR can provide imaging evidence for the diagnosis of colon cancer.

Results

The results display that Au NR@PAMAM-GX1 can specifically deliver FAM172A to cancer cells with excellent transfection efficiency. The HCT-8 cells treated with the Au NR@PAMAM-GX1/FAM172A under laser irradiation have a viability of 20.45%, which is much lower than the survival rate of other single-mode PTT treatment or single-mode gene therapy. Furthermore, animal experiment results confirm that Au NR@PAMAM-GX1/FAM172A complexes can achieve tumor thermal imaging, targeted CT imaging, PTT and gene therapy after tail vein injection.

Conclusion

Our findings demonstrate that the synthesized Au NR@PAMAM-GX1 offer a facile platform to exert antitumor and improve the diagnostic level of tumor.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02105-3.

Amplified plasmonic and microfluidic setup for DNA monitoring

Plasmonic nanosensors for label-free detection of DNA require excellent sensing resolution, which is crucial when monitoring short DNA sequences, as these induce tiny peak shifts, compared to large biomolecules. We report a versatile and simple strategy for plasmonic sensor signal enhancement by assembling multiple (four) plasmonic sensors in series. This approach provided a fourfold signal enhancement, increased signal-to-noise ratio, and improved sensitivity for DNA detection. The response of multiple sensors based on AuNSpheres was also compared with  AuNRods, the latter showing better sensing resolution. The amplification system based on AuNR was integrated into  a microfluidic sequential injection platform and applied to the monitoring of DNA, specifically from environmental invasive species-zebra mussels. DNA from zebra mussels was log concentration-dependent from 1 to 1 × 10⁶ pM, reaching a detection limit of 2.0 pM. In situ tests were also successfully applied to real samples, within less than 45 min, using DNA extracted from zebra mussel meat. The plasmonic nanosensors' signal can be used as a binary output (yes/no) to assess the presence of those invasive species. Even though these genosensors were applied to the monitoring of DNA in environmental samples, they potentially offer advantage in a wide range of fields, such as disease diagnostics.

How Do Proteins Associate with Nanoscale Metal-Organic Framework Surfaces?

It is well known that colloidal nanomaterials, upon exposure to a complex biological medium, acquire biomolecules on their surface to form coronas. Porous nanomaterials present an opportunity to sequester biomolecules and/or control their orientation at the surface. In this report, a metal-organic framework (MOF) shell around gold nanorods was compared to MOF nanocrystals as potential protein sponges to adsorb several common proteins (lysozyme, beta-lactoglobulin-A, and bovine serum albumin) and potentially control their orientation at the surface. Even after correction for surface area, MOF shell/gold nanorod materials adsorbed more protein than the analogous nanoMOFs. For the set of proteins and nanomaterials in this study, all protein-surface interactions were exothermic, as judged by isothermal titration calorimetry. Protein display at the surfaces was determined from limited proteolysis experiments, and it was found that protein orientation was dependent both on the nature of the nanoparticle surface and on the nature of the protein, with lysozyme and beta-lactoglobulin-A showing distinct molecular positioning.

The impacts of metal-based engineered nanomaterial mixtures on microbial systems: A review

The last decade has witnessed tremendous growth in the commercial use of metal-based engineered nanomaterials (ENMs) for a wide range of products and processes. Consequently, direct and indirect release into environmental systems may no longer be considered negligible or insignificant. Yet, there is an active debate as to whether there are real risks to human or ecological health with environmental exposure to ENMs. Previous research has focused primarily on the acute effects of individual ENMs using pure cultures under controlled laboratory environments, which may not accurately reveal the ecological impacts of ENMs under real environmental conditions. The goal of this review is to assess our current understanding of ENM effects as we move from exposure of single to multiple ENMs or microbial species. For instance, are ENMs' impacts on microbial communities predicted by their intrinsic physical or chemical characteristics or their effects on single microbial populations; how do chronic ENM interactions compare to acute toxicity; does behavior under simplified laboratory conditions reflect that in environmental media; finally, is biological stress modified by interactions in ENM mixtures relative to that of individual ENM? This review summarizes key findings and our evolving understanding of the ecological effects of ENMs under complex environmental conditions on microbial systems, identifies the gaps in our current knowledge, and indicates the direction of future research.

Programmable Self-Assembly of Gold Nanoarrows via Regioselective Adsorption

Programing the self-assembly of colloidal nanoparticles into predetermined superstructures represents an attractive strategy to realize functional assemblies and novel nanodevices, but it remains a challenge. Herein, gold nanoarrows (GNAs) showing a distinct convex-concave structure were employed as unique building blocks for programmable self-assembly involving multiple assembly modes. Regioselective adsorption of 1,10-decanedithiol on the vertexes, edges, and facets of GNAs allowed for programmable self-assembly of GNAs with five distinct assembly modes, and regioselective blocking with 1-dodecanethiol followed by adsorption of 1,10-decanedithiol gave rise to programmable self-assembly with six assembly modes including three novel wing-engaged modes. The assembly mode was essentially determined by regioselective adsorption of the dithiol linker dictated by the local curvature together with the shape complementarity of GNAs. This approach reveals how the geometric morphology of nanoparticles affects their regioselective functionalization and drives their self-assembly.

How to Utilize Excited Plasmon Energy Efficiently

Plasmonic nanoparticles can concentrate electromagnetic fields at the nanoscale and function as a powerful intermediary to enhance light-matter interactions. They have been widely employed for solar energy harvesting, photocatalysis, medicine, sensing, imaging, spectroscopy, optics, and optoelectronics. In this Perspective, we provide a brief overview of research progress in the utilization of excited plasmon energy, with emphasis on the charge- and energy-transfer processes. We discuss important factors that affect the charge- and energy-transfer efficiencies and present open questions and major challenges in the efficient utilization of excited plasmon energy.

Liquid-liquid interfacial self-assembled triangular Ag nanoplate-based high-density and ordered SERS-active arrays for the sensitive detection of dibutyl phthalate (DBP) in edible oils

DBP, one of the phthalic acid esters (PAEs), is known as an endocrine disruptor and is toxic to humans in abnormal concentrations. Here, a high-density and ordered SERS substrate based on the self-assembly of triangular Ag nanoplate (TAgNP) arrays is developed for DBP detection. Benefiting from the ordered arrangement and sharp corners of TAgNPS, the arrays can provide sufficient and uniform hotspots for reproducible and highly active SERS effects. Using Rhodamine 6G (R6G) as a reporter molecule, the SERS enhancement factor (EF) of the TAgNP arrays was found to be as high as 1.2 × 107 and the relative standard deviation was 6.56%. As a trial for practical applications, the TAgNP array substrates were used for the detection of dibutyl phthalate (DBP) in edible oils. In this assay, edible oil samples were added to hexane as an organic phase for the formation of the TAgNP arrays, which caused DBP to be loaded at hotspots. DBP in edible oils could be identified at concentrations as low as 10-7 M. This SERS substrate based on the TAgNP arrays has great potential applications in the high sensitivity and reproducible detection of contaminants in food.

Surface Engineering and Controlled Ripening for Seed-Mediated Growth of Au Islands on Au Nanocrystals

Engineering the nucleation and growth of plasmonic metals (Ag and Au) on their pre-existing seeds is expected to produce nanostructures with unconventional morphologies and plasmonic properties that may find unique applications in sensing, catalysis, and broadband energy harvesting. Typical seed-mediated growth processes take advantage of the perfect lattice match between the deposited metal and seeds to induce conformal coating, leading to either simple size increases (e.g., Au on Au) or the formation of core-shell structures (e.g., Ag on Au) with limited morphology change. In this work, we show that the introduction of a thin layer of metal with considerable lattice mismatch can effectively induce the nucleation of well-defined Au islands on Au nanocrystal seeds. By controlling the interfacial energy between the seed and the deposited material, the oxidative ripening, and the surface diffusion of metal precursors, we can regulate the number of islands on the seeds and produce complex Au nanostructures with morphologies tunable from core-satellites to tetramers, trimers, and dimers.

Designed Co-DNA-Locker and Ratiometric SERS Sensing for Accurate Detection of Exosomes Based on Gold Nanorod Arrays

Exosomes, which can transfer and deliver information about the original cell, are considered to be ideal candidates for early cancer diagnosis and evaluation of therapeutic efficacy due to their high abundance and stability. However, the highly expressed proteins on the surface of exosomes are usually associated with a variety of cancers; it is difficult to distinguish them by a single marker. Herein, a controlled self-assembly of gold nanorod (AuNR) arrays was prepared to construct a surface-enhanced Raman spectroscopy (SERS) sensor for the specific detection of exosomes secreted by SK-Br-3 cells based on a designed colocalization-dependent system (Co-DNA-Locker) and ratiometric strategy. After the exosomes are captured in the sensing array by the EpCAM aptamer modified on the surface of AuNRs, the DNA logic process occurs because the other two proteins, CD63 and HER2, are expressed simultaneously on the surface of exosomes secreted by SK-Br-3 cells, and the SERS signal intensity of the Rhodamine 6G (R6G) tagged on the terminal of DNA T_E increased with an increase in the concentration of the exosomes, while the SERS signal intensity of Cy5 linked on the terminal of the EpCAM aptamer, which acts as an internal standard, remains stable. The AuNRs are uniformly arranged in a hexagonal shape, and the dense "hot spots" produce "hot surfaces," which greatly improve the sensitivity and uniformity of detection. In the presence of target exosomes, the DNA colocalization three-signal input switch and the ratiometric strategy realize the specific and accurate detection of exosomes. This sensing strategy achieves a wide detection range (1.0 × 10⁴-5.0 × 10⁶ particles/mL) and a lower detection limit (5.3 × 10³ particles/mL), without using any signal amplification mechanism, demonstrating promising applications in health care monitoring and clinical diagnostics.

Great enhancement on two-photon photoluminescence imaging contrast of Au nanoparticles via double-pulse femtosecond laser excitation with controlled phase differences

Au nanoparticles are attractive contrast agents for noninvasive living tissue imaging with deep penetration because of their strong two-photon photoluminescence (TPPL) intensity and excellent biocompatibility. However, the inevitable phototoxicity and huge auto-fluorescence are consistently associated with laser excitation. Therefore, enhancement of TPPL intensity and suppression of backgrounds are always highly desired under the demand of reducing excitation powers. In this work, we develop a double-pulse TPPL (DP-TPPL) scheme with controlled phase differences (Δφ) between the double pulses to significantly improve the signal-to-noise ratio (SNR) of TPPL imaging. Under the modulated phase (Δφ periodically varying between 0-2π), our results show that SNR can be improved from 4.3 to 1715, with an enhancement of up to 400 folds at the integration of 50 ms. More importantly, this enhancement can be unlimitedly lifted by increasing the number of photons or integration times in principle. Further boosting has been achieved by reducing the magnitude of background noises; subsequently, SNR is improved by more than 10⁴ times. Our schemes offer great potential for reducing phototoxicity and extracting extremely weak signals from huge backgrounds and open up a new possibility for a rapid, flexible, and reliable medical diagnosis by TPPL imaging with diminished laser powers.

Computational Optimization of the Size of Gold Nanorods for Single-Molecule Plasmonic Biosensors Operating in Scattering and Absorption Modes

We present a comprehensive computational study on the optimization of the size of gold nanorods for single-molecule plasmonic sensing in terms of optical refractive index sensitivity. We construct an experimentally relevant model of single-molecule-single-nanoparticle sensor based on spherically capped gold nanorods, tip-specific functionalization and passivation layers, and biotin-streptavidin affinity system. We introduce a universal figure of merit for the sensitivity, termed contrast-to-noise ratio (CNR), which relates the change of measurable signal caused by the discrete molecule binding events to the inherent measurement noise. We investigate three distinct sensing modalities relying on direct spectral measurements, monitoring of scattering intensity at fixed wavelength and photothermal effect. By considering a shot-noise-limited performance of an experimental setup, we demonstrate the existence of an optimum nanorod size providing the highest sensitivity for each sensing technique. The optimization at constant illumination intensity (i.e., low-power applications) yields similar values of approximately 20 × 80 nm² for each considered sensing technique. Second, we investigate the impact of geometrical and material parameters of the molecule and the functionalization layer on the sensitivity. Finally, we discuss the variable illumination intensity for each nanorod size with the steady-state temperature increase as its limiting factor (i.e., high-power applications).

Au nanobipyramids with Pt decoration enveloped in TiO2 nanoboxes for photocatalytic reactions

Noble metal nanocrystals and core-shell nanocomposites have attracted particular interest due to their unique optical properties originating from surface plasmon resonance (SPR) and wide applications related to the SPR effect. In this work, we designed and fabricated a new Au-Pt@TiO₂ nanocomposite, in which Au nanobipyramids (AuNBPs) decorated with platinum (Pt) clusters were enveloped in mesoporous TiO₂ nanoboxes with nanocavities. AuNBPs provide strong SPR absorption and localized field enhancement restricted to the cavities of TiO₂ nanoboxes. The Pt nanoclusters decorated on the surface of AuNBPs can effectively modulate the charge movement and energy transfer in the photocatalytic process. The enhanced electric field provides a local thermal effect for the photocatalytic reaction and promotes the injection process of hot electrons which facilitates carrier separation. The nanoboxes with nanocavities can effectively manage the usage of localized energy and provide space for reaction. Under the cooperative effects, the photocatalytic performance was remarkably improved along with durability and stability. For the AuNBP-Pt@TiO₂ nanoboxes, the rhodamine-B degradation efficiency was ∼6.5 times that of AuNBP@TiO₂ nanoboxes. The mechanism of the photocatalysis process was proposed based on experimental results and simulations. Benefiting from the excellent structure and properties, the obtained nanostructure is a promising candidate in the fields of pollutant degradation and chemical reaction catalysis.

Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

There is an obvious gap between efforts dedicated to the control of chemicophysical and morphological properties of catalyst active phases and the attention paid to the search of new materials to be employed as functional carriers in the upgrading of heterogeneous catalysts. Economic constraints and common habits in preparing heterogeneous catalysts have narrowed the selection of active-phase carriers to a handful of materials: oxide-based ceramics (e.g. Al₂O₃, SiO₂, TiO₂, and aluminosilicates-zeolites) and carbon. However, these carriers occasionally face chemicophysical constraints that limit their application in catalysis. For instance, oxides are easily corroded by acids or bases, and carbon is not resistant to oxidation. Therefore, these carriers cannot be recycled. Moreover, the poor thermal conductivity of metal oxide carriers often translates into permanent alterations of the catalyst active sites (i.e. metal active-phase sintering) that compromise the catalyst performance and its lifetime on run. Therefore, the development of new carriers for the design and synthesis of advanced functional catalytic materials and processes is an urgent priority for the heterogeneous catalysis of the future. Silicon carbide (SiC) is a non-oxide semiconductor with unique chemicophysical properties that make it highly attractive in several branches of catalysis. Accordingly, the past decade has witnessed a large increase of reports dedicated to the design of SiC-based catalysts, also in light of a steadily growing portfolio of porous SiC materials covering a wide range of well-controlled pore structure and surface properties. This review article provides a comprehensive overview on the synthesis and use of macro/mesoporous SiC materials in catalysis, stressing their unique features for the design of efficient, cost-effective, and easy to scale-up heterogeneous catalysts, outlining their success where other and more classical oxide-based supports failed. All applications of SiC in catalysis will be reviewed from the perspective of a given chemical reaction, highlighting all improvements rising from the use of SiC in terms of activity, selectivity, and process sustainability. We feel that the experienced viewpoint of SiC-based catalyst producers and end users (these authors) and their critical presentation of a comprehensive overview on the applications of SiC in catalysis will help the readership to create its own opinion on the central role of SiC for the future of heterogeneous catalysis.

Nanoparticle-Assisted Sonosensitizers and Their Biomedical Applications

As a non-invasive strategy, sonodynamic therapy (SDT) which utilizes sonosensitizers to generate reactive oxygen species (ROS) has received significant interest over recent years due to its ability to break depth barrier. However, intrinsic limitations of traditional sonosensitizers hinder the widespread application of SDT. With the development of nanotechnology, various nanoparticles (NPs) have been designed and used to assist sonosensitizers for SDT. This review first summarizes the possible mechanisms of SDT, then classifies the NPs-assisted sonosensitizers and discusses their biomedical applications in ultrasonography, drug delivery, high intensity focused ultrasound and SDT-based combination treatment. Finally, some challenges and future perspectives of NPs-assisted SDT has also been discussed.

The polymeric glyco-linker controls the signal outputs for plasmonic gold nanorod biosensors due to biocorona formation

Gold nanorods (GNRs) are a promising platform for nanoplasmonic biosensing. The localised surface plasmon resonance (LSPR) peak of GNRs is located in the near-infrared optical window and is sensitive to local binding events, enabling label-free detection of biomarkers in complex biological fluids. A key challenge in the development of such sensors is achieving target affinity and selectivity, while both minimizing non-specific binding and maintaining colloidal stability. Herein, we reveal how GNRs decorated with galactosamine-terminated polymer ligands display significantly different binding responses in buffer compared to serum, due to biocorona formation, and how biocorona displacement due to lectin binding plays a key role in their optical responses. GNRs were coated with either poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA) or poly(N-hydroxyethyl acrylamide) (PHEA) prepared via reversible addition-fragmentation chain-transfer (RAFT) polymerisation and end-functionalised with galactosamine (Gal) as the lectin-targeting unit. In buffer Gal-PHEA-coated GNRs aggregated upon soybean agglutinin (SBA) addition, whereas Gal-PHPMA-coated GNRs exhibited a red-shift of the LSPR spectrum without aggregation. In contrast, when incubated in serum Gal-PHPMA-coated nanorods showed no binding response, while Gal-PHEA GNRs exhibited a dose-dependent blue-shift of the LSPR peak, which is the opposite direction (red-shift) to what was observed in buffer. This differential behaviour was attributed to biocorona formation onto both polymer-coated GNRs, shown by differential centrifugal sedimentation and nanoparticle tracking analysis. Upon addition of SBA to the Gal-PHEA coated nanorods, signal was generated due to displacement of weakly-bound biocorona components by lectin binding. However, in the case of Gal-PHPMA which had a thicker corona, attributed to lower polymer grafting densities, addition of SBA did not lead to biocorona displacement and there was no signal output. These results show that plasmonic optical responses in complex biological media can be significantly affected by biocorona formation, and that biocorona formation itself does not prevent sensing so long as its exact nature (e.g. 'hard versus soft') is tuned.

Optimization of plasmonic metal structures for improving the hydrogen production efficiency of metal-organic frameworks

The introduction of plasmonic metals of gold (Au) nanoparticles onto metal-organic frameworks (MOFs) has been testified as an efficient approach to boost the H2 evolution ability because the excited Au particles can generate hot electrons that can then be injected into MOFs to inhibit the recombination of charges. Generally, Au particles possess two modes of polarization, which are transverse and longitudinal polarizations. However, which of the two modes is more efficient remains unclear and is yet to be disclosed. Herein, we report a strategy of finely controlling the transverse and longitudinal polarizations by gradually reducing the length, without changing the width of Au rods, and then combining with MOF Pt@MIL-125 to construct Pt@MIL-125/Au Schottky junctions, for investigating the polarization mode effects. The results indicate that with the reduction in the length of Au rods from 67 nm to 38 nm, the transverse polarization will be increased, which can lead to a significant enhancement in the electron-hole separation efficiency and H2 generation activity. When Au is in spherical shape, the transverse polarization effect reaches the highest level, thereby achieving the highest H2 production rate of 265.1 μmol g-1 h, which is 1.6 times more than that of 67 nm Au rods. The enhancement can be attributed to the significant accelerated electron transfer rate induced by transverse polarization and evidenced by ESR analysis. The results indicate that the transverse polarization is more efficient for hot electron injection and highlight that the Au sphere is a more appropriate candidate for producing the maximum SPR effect during photocatalysis.

Facet- and Gas-Dependent Reshaping of Au Nanoplates by Plasma Treatment

The reshaping of metal nanocrystals on substrates is usually realized by pulsed laser irradiation or ion-beam milling with complex procedures. In this work, we demonstrate a simple method for reshaping immobilized Au nanoplates through plasma treatment. Au nanoplates can be reshaped gradually with nearly periodic right pyramid arrays formed on the surface of the nanoplates. The gaseous environment in the plasma-treatment system plays a significant role in the reshaping process with only nitrogen-containing environments leading to reshaping. The reshaping phenomenon is facet-dependent, with right pyramids formed only on the exposed {111} facets of the Au nanoplates. The morphological change of the Au nanoplates induced by the plasma treatment leads to large plasmon peak redshifts. The reshaped Au nanoplates possess slightly higher refractive index sensitivities and largely increased surface-enhanced Raman scattering intensities compared to the flat, untreated nanoplates. Our results offer insights for studying the interaction mechanism between plasma and the different facets of noble metal nanocrystals and an approach for reshaping light-interacting noble metal nanocrystals.

Electrostatically self-assembled gold nanorods with chondroitin sulfate for targeted photothermal therapy for melanoma

BACKGROUND

The application of gold nanorods (GNRs) in photothermal therapy is a promising avenue for cancer treatment. The aim of this study was to develop a GNR-based targeted photothermal therapy for melanoma.

METHODS

We utilized the electrostatic interaction between cationic GNRs and an anionic polymer chondroitin sulfate A (CSA), which has an affinity for binding to melanoma cells, to construct an anionic binary GNR-CSA complex (GNR-CS) at an optimal theoretical charge ratio of the trimethylammonium groups of GNR: carboxyl and sulfate groups of CSA = 1:2.5. The cytotoxicity to normal cells and erythrocyte agglutination activity of GNR-CS were evaluated. After the cellular uptake of GNR-CS by melanoma cells (B16-F10) was investigated, the photothermal performance of GNR-CS against B16-F10 cells was evaluated in vitro.

RESULTS

The particle size and zeta potential of GNR-CS were approximately 35 nm and -20 mV, respectively. GNR-CS showed little cytotoxicity to normal cells and low erythrocyte agglutination activity, indicating good biocompatibility. Compared with negatively-charged GNR, GNR-CS was highly taken up by B16-F10 cells even if it was negatively charged. Cellular uptake was significantly suppressed upon treatment with excess CSA, suggesting the involvement of a CSA-specific uptake pathway. Furthermore, irradiation of the GNR-CS solution with near-infrared (NIR) light increased its temperature in light-intensity and GNR-concentration dependent manners. GNR-CS exhibited significant and GNR-dose dependent cytotoxicity in melanoma cells in combination with NIR light irradiation.

CONCLUSION

GNRs coated with CSA have the potential as a medicine in targeted photothermal therapy for melanoma.

Rapid controlled synthesis of gold-platinum nanorods with excellent photothermal properties under 808 nm excitation

Noble metal nanomaterials are particularly suitable as photothermal transduction agents (PTAs) with high photothermal conversion efficiency (PCE) due to local surface plasmon resonance (LSPR). Studies on different gold-platinum (Au-Pt) bimetal nanoparticles exhibiting the LSPR effect have provided a new idea for the synthesis of excellent PTAs. But there is no simple and scalable method for the controllable synthesis of Au-Pt nanoparticles with adjustable LSPR wavelength range. In this work, the effects of Ag+ and K2PtCl4 on the deposition of Pt on the surface of gold nanorods (AuNRs) were investigated. A fast, precise, and controlled synthesis of dumbbell-like Pt-coated AuNRs (Au@Pt NRs) under mild conditions is proposed. The synthesized Au@Pt NRs have a longitudinal LSPR wavelength of 812 nm, which is very close to a common laser wavelength of 808 nm. The Au@Pt NRs exhibit excellent photothermal properties when irradiated with a laser. The temperature increased by more than 36 °C after irradiation for 10 min, with a PCE of about 78.77%, which is much higher than that of AuNRs (57.33%). In addition, even after four on/off cycles, the Au@Pt NRs are able to maintain the photothermal properties and retain their optical properties, indicating that they have excellent photothermal stability and reusability.

General Surface-Enhanced Raman Spectroscopy Method for Actively Capturing Target Molecules in Small Gaps

Over the past decade, many efforts have been devoted to designing and fabricating substrates for surface-enhanced Raman spectroscopy (SERS) with abundant hot spots to improve the sensitivity of detection. However, there have been many difficulties involved in causing molecules to enter hot spots actively or effectively. Here, we report a general SERS method for actively capturing target molecules in small gaps (hot spots) by constructing a nanocapillary pumping model. The ubiquity of hot spots and the inevitability of molecules entering them lights up all the hot spots and makes them effective. This general method can realize the highly sensitive detection of different types of molecules, including organic pollutants, drugs, poisons, toxins, pesticide residues, dyes, antibiotics, amino acids, antitumor drugs, explosives, and plasticizers. Additionally, in the dynamic detection process, an efficient and stable signal can be maintained for 1-2 min, which increases the practicality and operability of this method. Moreover, a dynamic detection process like this corresponds to the processes of material transformation in some organisms, so the method can be used to monitor transformation processes such as the death of a single cell caused by photothermal stimulation. Our method provides a novel pathway for generating hot spots that actively attract target molecules, and it can achieve general ultratrace detection of diverse substances and be applied to the study of cell behaviors in biological systems.

Integration of antimicrobial peptides and gold nanorods for bimodal antibacterial applications

The misuse and abuse of antibiotics have given rise to a severe problem of the drug resistance of bacteria. Solving this problem has been a vitally important task in the modern medical arena. In this work, an antimicrobial peptide (AMP), BF2b, and gold nanorods (AuNRs) were used to develop a specific drug delivery system for killing methicillin-resistant Staphylococcus aureus (MRSA). On the one hand, BF2b has unique anti-bacterial performance and has a lower tendency than traditional antibiotics to engender the drug resistance of bacteria. On the other hand, AuNRs have diverse distinct properties, such as photo-thermal conversion, which can be employed for photo-thermal sterilization. We aimed to integrate the anti-bacterial activity of BF2b and the photo-thermal sterilization of AuNRs to kill drug-resistant bacteria. Fourier-transform infrared spectroscopy, microBCA and zeta potential measurements were utilized to characterize the product, AuNR@PEG/BF2b. Transmittance electron microscopy, UV-vis spectroscopy and photothermal conversion measurement were conducted to verify the stability and photothermal conversion capacity of AuNR@PEG/BF2b. Cell viability and hemolysis assay were carried out to test the biocompatibility of AuNR@PEG/BF2b. Finally, the in vitro and in vivo experiments were performed to demonstrate the excellent bactericidal activity of AuNR@PEG/BF2b.

DNA-encoded bimetallic Au-Pt dumbbell nanozyme for high-performance detection and eradication of Escherichia coli O157:H7

Infectious Escherichia coli O157:H7 threatens the health of millions people each year. Thus, it is important to establish a simple and sensitive method for bacterial detection and eradication. Herein, a DNA-programming strategy is explored to synthesize anisotropic dumbbell-like Au-Pt nanoparticles with excellent catalytic and anti-bacterial activities, which were applied in the simultaneous detection and eradication of pathogenic bacteria. The DNA sequence-dependent growth of bimetallic nanoparticles is firstly studied and polyT20 has the tendency to form dumbbell-like Au-Pt bimetallic structures based on gold nanorods seeds. PolyA20 and polyC20 can also form similar structures but only at much lower DNA concentrations, which can be explained by their much higher affinity to the metal surfaces than T20. The as-prepared nanoparticles exhibit high nanozyme catalytic activity resulting from the synergistic effect of Au and Pt. Under light irradiation, the Au-Pt nanoparticles show high photothermal conversion efficiency and enhanced catalytic activity, which can be applied for the eradication and detection of E. coli O157:H7 with a robust efficacy (95%) in 5 min and provides excellent linear detection (10-10⁷ CFU/mL), with a detection limit of 2 CFU/mL. This study offered new insights into DNA-directed synthesis of nanomaterials with excellent biosensing and antibiotic applications.

Providing Multicolor Plasmonic Patterns with Au@Ag Core-Shell Nanostructures for Visual Discrimination of Biogenic Amines

Biogenic amines (BAs) are known as substantial indicators of the quality and safety of food. Developing rapid and visual detection methods capable of simultaneously monitoring BAs is highly desired due to their harmful effects on human health. In the present study, we have designed a multicolor sensor array consisting of two types of gold nanostructures (i.e., gold nanorods (AuNRs) and gold nanospheres (AuNSs)) for the discrimination and determination of critical BAs (i.e., spermine (SM), tryptamine (TT), ethylenediamine (EA), tyramine (TR), spermidine (SD), and histamine (HT)). The design principle of the probe was based on the metallization of silver ions on the surface of AuNRs and AuNSs in the presence of BAs, forming Au@Ag core-shell nanoparticles. Changes in the surface composition, size, and aspect ratio of AuNSs and AuNRs induced a blue shift in the plasmonic band, which was accompanied by sharp and rainbowlike color variations in the solution. The collected data were visually assessed and statistically analyzed by various data visualization and pattern recognition methods. Namely, linear discriminant analysis (LDA) and partial least squares (PLS) regression were employed for the qualitative and quantitative determination of BAs. The responses were linearly correlated to the concentrations of BAs in a wide range of 10-800, 20-800, 40-800, 40-800, 60-800, and 80-800 μmol L^-1 with the limit of detections of 2.46, 4.79, 8.58, 14.26, 10.03, and 27.29 μmol L^-1 for SD, SM, TT, HT, EA, and TR, respectively. Finally, the practical applicability of the sensor array was investigated by the determination of BAs in meat and fish samples by which the potential of the probe for on-site determination of food freshness/spoilage was successfully verified.

Biosensing Applications Using Nanostructure-Based Localized Surface Plasmon Resonance Sensors

Localized surface plasmon resonance (LSPR)-based biosensors have recently garnered increasing attention due to their potential to allow label-free, portable, low-cost, and real-time monitoring of diverse analytes. Recent developments in this technology have focused on biochemical markers in clinical and environmental settings coupled with advances in nanostructure technology. Therefore, this review focuses on the recent advances in LSPR-based biosensor technology for the detection of diverse chemicals and biomolecules. Moreover, we also provide recent examples of sensing strategies based on diverse nanostructure platforms, in addition to their advantages and limitations. Finally, this review discusses potential strategies for the development of biosensors with enhanced sensing performance.

Gold Nanomaterials as a Promising Integrated Tool for Diagnosis and Treatment of Pathogenic Infections-A Review

This review summarizes research on functionalized gold nanomaterials as pathogen detection sensors and pathogen elimination integrated tools. After presenting the challenge of current severe threat from pathogenic bacteria and the increasingly serious growth rate of drug resistance, the first section mainly introduces the conspectus of gold nanostructures from synthesis, characterization, physicochemical properties and applications of gold nanomaterials. The next section deals with gold nanomaterials-based pathogen detection sensors such as colorimetric sensors, fluorescence sensors and Surface-Enhanced Raman Scattering sensors. We then discuss strategies based on gold nanomaterials for eliminating pathogenic infections, such as the dual sterilization strategy for grafting gold nanomaterials with antibacterial substances, photothermal antibacterial and photodynamic antibacterial methods. The fourth part briefly introduces the comprehensive strategy for diagnosis and sterilization of pathogen infection based on gold nanomaterials, such as the diagnosis and treatment strategy for pathogen infection using Roman signals real-time monitoring and photothermal sterilization. A concluding section that summarizes the current status and challenges of the novel diagnosis and treatment integrated strategy for pathogenic infections, gives an outlook on potential future perspectives.

Tunable Size Dependence of Quantum Plasmon of Charged Gold Nanoparticles

The quantum behavior of surface plasmons has received extensive attention, benefiting from the development of exquisite nanotechnology and the diverse applications. Blueshift, redshift, and nonshift of localized surface plasmon resonances (LSPRs) have all been reported as the particle size decreases and enters the quantum size regime, but the underlying physical mechanism to induce these controversial size dependences is not clear. Herein, we propose an improved semiclassical model for modifying the dielectric function of metal nanospheres by combining the intrinsic quantized electron transitions and surface electron injection or extraction to investigate the plasmon shift and LSPR size dependence of the charged Au nanoparticles. We experimentally observe that the nonmonotonic blueshift of LSPRs with size for Au nanoparticles is turned into an approximately monotonic blueshift by increasing the electron donor concentration in the reduction solution, and it can also be transformed to an approximately monotonic redshift after surface passivation by ligand molecules. Moreover, we demonstrate controlled blueshift and redshift for the electron and hole plasmons in Cu_{2-x}S@Au core-shell nanoparticles by injecting electrons. The experimental observations and the theoretical calculations clarify the controversial size dependences of LSPR reported in the literature, reveal the critical role of surface electron injection or extraction in the transformation between the different size dependences of LSPRs, and are helpful for understanding the nature of surface plasmons in the quantum size regime.

Strong Light-Matter Interactions in Chiral Plasmonic-Excitonic Systems Assembled on DNA Origami

The exploitation of strong light-matter interactions in chiral plasmonic nanocavities may enable exceptional physical phenomena and lead to potential applications in nanophotonics, information communication, etc. Therefore, a deep understanding of strong light-matter interactions in chiral plasmonic-excitonic (plexcitonic) systems constructed by a chiral plasmonic nanocavity and molecular excitons is urgently needed. Herein, we systematically studied the strong light-matter interactions in gold nanorod-based chiral plexcitonic systems assembled on DNA origami. Rabi splitting and anticrossing behavior were observed in circular dichroism spectra, manifesting chiroptical characteristic hybridization. The bisignate line shape of the circular dichroism (CD) signal allows the accurate discrimination of hybrid modes. A large Rabi splitting of ∼205/∼199 meV for left-handed/right-handed plexcitonic nanosystems meets the criterion of strong coupling. Our work deepens the understanding of light-matter interactions in chiral plexcitonic nanosystems and will facilitate the development of chiral quantum optics and chiroptical devices.

Many Birds, One Stone: A Smart Nanodevice for Ratiometric Dual-Spectrum Assay of Intracellular MicroRNA and Multimodal Synergetic Cancer Therapy

The development of a theragnostic platform integrating precise diagnosis and effective treatment is significant but still extremely challenging. Herein, an integrated smart nanodevice composed of Au@Cu_2-xS@polydopamine nanoparticles (ACSPs) and fuel DNA-conjugated tetrahedral DNA nanostructures (fTDNs) was constructed, in which the ACSP nanoprobe played multiple key roles in antitumor therapy as well as in situ monitoring of microRNAs (miRNAs) in cancer cells. Regarding the analysis, the ACSP probe contained two optical properties: excellent surface-enhanced Raman scattering (SERS) enhancement and high fluorescence (FL) quenching performance. Employing the ACSPs as the high-efficiency detection substrate combined with the fTDN-assisted DNA walking nanomachines as the superior amplification strategy, a SERS-FL dual-spectrum biosensor was constructed, which achieved an ultralow background signal and excellent sensitivity with detection limits of 0.11 pM and 4.95 aM by FL and SERS, respectively. Moreover, the rapid FL imaging and precise SERS quantitative detection for miRNA in cancer cells were also achieved by dual-signal ratio strategy, improving the accuracy of diagnosis. Regarding the therapeutic application, due to the high reactive oxygen species generation ability and excellent photothermal conversion efficiency, the ACSPs can also act as an all-in-one nanoagent for multimodal collaborative tumor therapy. Significantly, both in vivo and in vitro experiments confirmed its high biological safety and strong anticancer effect, indicating its promising theragnostic applications.

Gold Nanoparticles in Cancer Theranostics

Conventional cancer treatments, such as surgical resection, radiotherapy, and chemotherapy, have achieved significant progress in cancer therapy. Nevertheless, some limitations (such as toxic side effects) are still existing for conventional therapies, which motivate efforts toward developing novel theranostic avenues. Owning many merits such as easy surface modification, unique optical properties, and high biocompatibility, gold nanoparticles (AuNPs and GNPs) have been engineered to serve as targeted delivery vehicles, molecular probes, sensors, and so on. Their small size and surface characteristics enable them to extravasate and access the tumor microenvironment (TME), which is a promising solution to realize highly effective treatments. Moreover, stimuli-responsive properties (respond to hypoxia and acidic pH) of nanoparticles to TME enable GNPs’ unrivaled control for effective transport of therapeutic cargos. In this review article, we primarily introduce the basic properties of GNPs, further discuss the recent progress in gold nanoparticles for cancer theranostics, with an additional concern about TME stimuli-responsive studies.

Seed-Mediated Synthesis of Gold Nanorods at Low Concentrations of CTAB

Although gold nanorods capped with hexadecyltrimethylammonium bromide (CTAB) have been prepared through the seed-mediated method for their use in diagnostics and therapeutics, the toxicity of AuNRs@CTAB limits their practical applications in the biomedical field. In this work, the synthesis and tuning of gold nanorods at very low concentrations of CTAB (as low as 0.008 M) was successfully achieved by using the seed-mediated method. Furthermore, we managed to optimize the growth conditions by changing the amount of seeds, AgNO₃, and/or HCl. At low CTAB concentrations, gold nanorods with tunable size and aspect ratio, high monodispersity, and high purity were obtained and studied by UV-vis spectroscopy, transmission electron microscopy, and Mie-Gans theoretical calculations. This work revealed a method of nanoparticle growth that may be extended to synthesize other nanomaterials such as Ag, Cu, Pd, and Pt at such low CTAB concentrations.

Structural Control over Bimetallic Core-Shell Nanorods for Surface-Enhanced Raman Spectroscopy

Bimetallic nanorods are important colloidal nanoparticles for optical applications, sensing, and light-enhanced catalysis due to their versatile plasmonic properties. However, tuning the plasmonic resonances is challenging as it requires a simultaneous control over the particle shape, shell thickness, and morphology. Here, we show that we have full control over these parameters by performing metal overgrowth on gold nanorods within a mesoporous silica shell, resulting in Au-Ag, Au-Pd, and Au-Pt core-shell nanorods with precisely tunable plasmonic properties. The metal shell thickness was regulated via the precursor concentration and reaction time in the metal overgrowth. Control over the shell morphology was achieved via a thermal annealing, enabling a transition from rough nonepitaxial to smooth epitaxial Pd shells while retaining the anisotropic rod shape. The core-shell synthesis was successfully scaled up from micro- to milligrams, by controlling the kinetics of the metal overgrowth via the pH. By carefully tuning the structure, we optimized the plasmonic properties of the bimetallic core-shell nanorods for surface-enhanced Raman spectroscopy. The Raman signal was the most strongly enhanced by the Au core-Ag shell nanorods, which we explain using finite-difference time-domain calculations.

Tuning the Surface Plasmon Resonance of Gold Dumbbell Nanorods

Gold has always fascinated humans, occupying an important functional and symbolic role in civilization. In earlier times, gold was predominantly used in jewelry; today, this noble metal's surface properties are taken advantage of in catalysis and plasmonics. In this article, the plasmon resonance of gold dumbbell nanorods is investigated. This unusual morphology was obtained by a seed-mediated growth method. The concentration of chemical precursors such as cetyltrimethylammonium bromide and silver nitrate plays a significant role in controlling the shape of the nanorods. Indeed, the aspect ratio of dumbbell nanostructures was varied from 2.6 to 4. UV-visible absorption spectra revealed a shift of the longitudinal surface plasmon resonance peak from 669 to 789 nm. Having the plasmon resonance in the near infrared region helps to use those nanostructures as photothermal agents.

Single-strand DNA-nanorod conjugates - tunable anisotropic colloids for on-demand self-assembly

Directed self-assembly uses different stimuli to initiate and control the interaction between nanocrystals. Protonation at reduced pH represents a convenient stimulus for initiating self-assembly. Prior work has focused on protonation-induced hydrogen bonding between peptide or amino acid functionalized nanocrystals for reversible cycling between dispersed and aggregated states. Here, we discuss a fundamentally different approach, in which changes in pH modify the nonspecific interparticle interaction between Au nanorods conjugated with single-stranded (ss) DNA. While electrostatic repulsion stabilizes dispersed suspensions at neutral pH, protonation in acidic solution modifies the DNA corona, turning the interaction between the rods attractive and triggering their self-assembly. Analysis of in-situ electron microscopy of ssDNA-Au nanorods in solution is consistent with a van der Waals attraction of charge-neutral monomers at acidic pH. The results demonstrate ssDNA-conjugated anisotropic nanostructures as versatile building blocks with stimuli-programmable interactions for on-demand self-assembly.

Molecular Modeling and Simulation of Polymer Nanocomposites with Nanorod Fillers

We present a coarse-grained (CG) molecular dynamics (MD) simulation study of polymer nanocomposites (PNCs) containing nanorods with homogeneous and patchy surface chemistry/functionalization, modeled with isotropic and directional nanorod-nanorod attraction, respectively. We show how the PNC morphology is impacted by the nanorod design (i.e., aspect ratio, homogeneous or patchy surface chemistry/functionalization) for nanorods with a diameter equal to the Kuhn length of the polymer in the matrix. For PNCs with 10 vol % nanorods that have an aspect ratio ≤5, we observe percolated morphology with directional nanorod-nanorod attraction and phase-separated (i.e., nanorod aggregation) morphology with isotropic nanorod-nanorod attraction. In contrast, for nanorods with higher aspect ratios, both types of attractions result in aggregated nanorods morphology due to the dominance of entropic driving forces that cause long nanorods to form orientationally ordered aggregates. For most PNCs with isotropic or directional nanorod-nanorod attractions, the average matrix polymer conformation is not perturbed by the inclusion of up to 20 vol % nanorods. The polymer chains in contact with nanorods (i.e., interfacial chains) are on average extended and statistically different from the conformations the matrix chains adopt in the pure melt state (with no nanorods); in contrast, the polymer chains far from nanorods (i.e., bulk chains) adopt the same conformations as the matrix chains adopt in the pure melt state. We also study the effect of other parameters, such as attraction strength, nanorod volume fraction, and matrix chain length, for PNCs with isotropic or directional nanorod-nanorod attractions. Collectively, our results provide valuable design rules to achieve specific PNC morphologies (i.e., dispersed, aggregated, percolated, and orientationally aligned nanorods) for various potential applications.

Structure and luminescence of DNA-templated silver clusters

DNA serves as a versatile template for few-atom silver clusters and their organized self-assembly. These clusters possess unique structural and photophysical properties that are programmed into the DNA template sequence, resulting in a rich palette of fluorophores which hold promise as chemical and biomolecular sensors, biolabels, and nanophotonic elements. Here, we review recent advances in the fundamental understanding of DNA-templated silver clusters (Ag N -DNAs), including the role played by the silver-mediated DNA complexes which are synthetic precursors to Ag N -DNAs, structure-property relations of Ag N -DNAs, and the excited state dynamics leading to fluorescence in these clusters. We also summarize the current understanding of how DNA sequence selects the properties of Ag N -DNAs and how sequence can be harnessed for informed design and for ordered multi-cluster assembly. To catalyze future research, we end with a discussion of several opportunities and challenges, both fundamental and applied, for the Ag N -DNA research community. A comprehensive fundamental understanding of this class of metal cluster fluorophores can provide the basis for rational design and for advancement of their applications in fluorescence-based sensing, biosciences, nanophotonics, and catalysis.

Geometry-induced enhancement factor improvement in covered-gold-nanorod-dimer antennas

Illuminated gapped-gold-nanorod dimers hold surface plasmon polaritons (SPPs) that can be engineered, by an appropriate choice of geometrical parameters, to enhance the electromagnetic field at the gap, allowing applications in molecular detection via surface-enhanced Raman spectroscopy (SERS). Envisioning hybrid devices in which the SERS spectroscopy of molecules in the gap is complemented by electrical measurements, it arises the question of designing efficient geometries to contact the nanorods without decreasing the enhancement factor (EF) of the nanoantenna, i.e., the figure of merit for SERS spectroscopy. Within this framework we theoretically study the feasibility to fabricate designs based on covering with gold the far-from-the-gap areas of the dimer. We show that by tuning the geometrical parameters of the designs these systems can reach enhancement factors larger than the best achieved in the uncovered dimer: this supremacy survives even in the presence of dimer asymmetries and vacancies at the interfaces between the nanorods and the covering layers. Our results show that geometrical modifications away from the gap can improve the optical response at the gap, thus enabling the use of these devices both for hybrid and optical applications.

Morphology-Invariant Metallic Nanoparticles with Tunable Plasmonic Properties

Current methods for tuning the plasmonic properties of metallic nanoparticles typically rely on alternating the morphology (i.e., size and/or shape) of nanoparticles. The variation of morphology of plasmonic nanoparticles oftentimes impairs their performance in certain applications. In this study, we report an effective approach based on the control of internal structure to engineer morphology-invariant nanoparticles with tunable plasmonic properties. Specifically, these nanoparticles were prepared through selective growth of Ag on the inner surfaces of preformed Ag-Au alloyed nanocages as the seeds to form Ag@(Ag-Au) shell@shell nanocages. Plasmonic properties of the Ag@(Ag-Au) nanocages can be conveniently and effectively tuned by varying the amount of Ag deposited on the inner surfaces, during which the overall morphology of the nanocages remains unchanged. To demonstrate the potential applications of the Ag@(Ag-Au) nanocages, they were applied to colorimetric sensing of human carcinoembryonic antigen (CEA) that achieved low detection limits. This work provides a meaningful concept to design and craft plasmonic nanoparticles.