Simple and Rapid High-Yield Synthesis and Size Sorting of Multibranched Hollow Gold Nanoparticles with Highly Tunable NIR Plasmon Resonances

Continuous Anisotropic Growth of Plasmonic CsxWO3-δ Nanocrystals into Rods and Platelets

Shape control during nanocrystal synthesis enables tunable physicochemical properties that emerge at the nanoscale. While extensive efforts have been devoted to controlling shapes in various systems such as plasmonic metal nanoparticles or semiconductor quantum dots, the shape control of plasmonic doped semiconductor nanocrystals remains less explored and limited. Here, we report the synthesis of CsxWO3-δ nanocrystals with exquisite shape control achieved through a continuous injection synthesis combined with precursor-mediated facet-selective growth. We demonstrate that the anisotropic growth of CsxWO3-δ nanocrystals is strongly dependent on the precursor injection rate, which we attribute to the material's intrinsic structural anisotropy and the contrasting reaction kinetics on different crystallographic facets. Furthermore, we reveal that the presence of halide ions in the reaction medium is critical for passivating and suppressing the growth of Cs-exposed basal planes. By systematically modulating the shape aspect ratio, we achieved an extended range of nanocrystal morphologies, leading to a broad tunability of LSPR spectra, spanning the entire near-infrared region and extending into the mid-infrared. Computational simulations effectively reproduce the observed shape-dependent optical properties and highlight the size-dependent damping behavior consistent with the free electron model. These findings provide a robust experimental methodology for shape control in structurally anisotropic nanocrystals and offer theoretical insights into the tunable LSPR properties of heavily doped plasmonic semiconductor systems.

Novel Microsynthesis of High-Yield Gold Nanoparticles to Accelerate Research in Biosensing and Other Bioapplications

Gold nanoparticles (AuNPs) exhibit unique properties that make them appealing for applications in biosensing and other emerging fields. Despite the availability of numerous synthesis methods, important questions remain to be addressed regarding the volume effect on the synthesis yield and quality of AuNPs in the light of biosensing research. The present study addresses these issues by developing a novel microvolumetric citrate-reduction method to improve the synthesis of AuNPs, which were characterized by electronic microscopy, energy dispersive spectroscopy, zeta potential and colorimetric analysis. A comparison of the novel microsynthesis method with the standard Turkevich method demonstrated its superior performance in terms of yield, monodispersity, rapidity (in one step), reproducibility, and stability. The analytical behavior of AuNPs-based aptasensors prepared by microsynthesis was investigated using kanamycin detection and showed higher reproducibility and improved detection limits (3.4 times) compared to those of Turkevich AuNPs. Finally, the effect of pH was studied to demonstrate the suitability of the method for the screening of AuNP synthesis parameters that are of direct interest in biosensing research; the results showed an optimal pH range between 5.0 and 5.5. In summary, the approach described herein has the potential to improve research capabilities in biosensing, with the added benefits of lowering costs and minimizing waste generation in line with current trends in green nanotechnology.

High-efficiency SERS platform based on 3D porous PPDA@Au NPs as a substrate for the detection of pesticides on vegetables

Nowadays, the presence of highly toxic and persistent residues of pesticides in water and food around the world is becoming a serious problem, and so their rapid and sensitive detection is critical to human health. In this work, a 3D composite nanoparticle of porous PDA (polydopamine) microspheres and Au NPs (PPDA@Au NPs) was proposed as a SERS substrate to detect pesticides. Porous PDA as a substrate was first synthesized with F127 (Pluronic F127), dopamine hydrochloride, and 1,3,5-TMB (1,3,5-trimethylbenzene) under weakly alkaline conditions by a one-step method. Then, HAuCl4 was in situ reduced in the pores of PPDA spheres and grew sequentially for effecting the reducibility of PPDA. As a result, uniform 3D PPDA@Au NPs with "hot spots" were successfully synthesized as SERS substrates, which could effectively avoid the agglomeration of gold nanoparticles to greatly improve the sensitivity and uniformity of the SERS platform. At the same time, methyl parathion, 4-chlorophenol, and 2,4-D as representatives of pesticides were detected with the proposed PPDA@Au NP-based SERS platform, with detection limits lower than 7.26, 7.52, and 11 ng mL-1, separately. The current work presents a simple preparation method to prepare sensitive and uniform SERS platform PPDA@Au NPs, which have potential for applications in actual pesticide and drug testing.

Controllable preparation of mesoporous spike gold nanocrystals for surface-enhanced Raman spectroscopy detection of micro/nanoplastics in water

Microplastics and nanoplastics are emerging classes of environmental contaminants that pose significant threats to human health. In particular, small nanoplastics (<1 μm) have drawn considerable attention owing to their adverse effects on human health; for example, nanoplastics have been found in the placenta and blood. However, reliable detection techniques are lacking. In this study, we developed a fast detection method that combines membrane filtration technology and surface-enhanced Raman spectroscopy (SERS), which can simultaneously enrich and detect nanoplastics with sizes as small as 20 nm. First, we synthesized spiked gold nanocrystals (Au NCs), achieving a controlled preparation of thorns ranging from 25 nm to 200 nm and regulating the number of thorns. Subsequently, mesoporous spiked Au NCs were homogeneously deposited on a glass fiber filter membrane to form an Au film as a SERS sensor. The Au-film SERS sensor achieved in-situ enrichment and sensitive SERS detection of micro/nanoplastics in water. Additionally, it eliminated sample transfer and prevented the loss of small nanoplastics. Using the Au-film SERS sensor, we detected 20 nm to 10 μm standard polystyrene (PS) microspheres with a detection limit of 0.1 mg/L. We also realized the detection of 100 nm PS nanoplastics at the 0.1 mg/L level in tap water and rainwater. This sensor provides a potential tool for rapid and susceptible on-site detection of micro/nanoplastics, especially small-sized nanoplastics.

Challenges and opportunities for SERS in the infrared: materials and methods

In the wake of a global, heightened interest towards biomarker and disease detection prompted by the SARS-CoV-2 pandemic, surface enhanced Raman spectroscopy (SERS) positions itself again at the forefront of biosensing innovation. But is it ready to move from the laboratory to the clinic? This review presents the challenges associated with the application of SERS to the biomedical field, and thus, to the use of excitation sources in the near infrared, where biological windows allow for cell and through-tissue measurements. Two main tackling strategies will be discussed: (1) acting on the design of the enhancing substrate, which includes manipulation of nanoparticle shape, material, and supramolecular architecture, and (2) acting on the spectral collection set-up. A final perspective highlights the upcoming scientific and technological bets that need to be won in order for SERS to stably transition from benchtop to bedside.

Functionalization of Gold Nanostars with Melamine for Colorimetric Detection of Uric Acid

Gold nanostars (AuNSs) are synthesized using a seed-mediated growth method. The synthesized AuNSs solution is stable and shows a localized surface plasmon resonance (LSPR) band in the visible range, which is confirmed using ultraviolet-visible (UV-Vis) spectroscopy. Furthermore, the as-synthesized AuNSs were functionalized with melamine and used as a sensor for the colorimetric detection of uric acid (UA). The detection mechanism could be assessed through various analytical techniques such as UV-Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), zeta potential, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopic techniques. These methods exhibited a good linear regression between the absorption ratio of LSPR band of melamine-AuNSs and the concentration of UA (0-120 µM), with the detection limit of 8.50 nm. As a result, UA was quantitatively detected in biofluids by using melamine-AuNSs as a colorimetric sensor, revealing melamine-AuNSs-based colorimetric approach which could be used as a simple platform for UA assay in biofluids.

A Versatile Synthetic Pathway for Producing Mesostructured Plasmonic Nanostructures

Highly branched gold (Au) nanostructures with sharp tips are considered excellent substrates for surface-enhanced Raman scattering (SERS)-based sensing technologies. Here, a simple synthetic route for producing Au or Au-Ag bimetallic mesostructures with multiple sharpened tips in the presence of carbon quantum dots (CQDs) is presented. The morphologies of these mesostructured plasmonic nanoparticles (MSPNs) can be controlled by adjusting the concentration of CQDs, reaction temperatures, and seed particles. The optimal molar ratio for [HAuCl₄ ]/[CQDs] is found to be ≈25. At this molar ratio, the diameters of MSPNs can be tuned from 80 to 200 nm by changing the reaction temperature from 25 to 80 °C. In addition, it is found that hierarchical MSPNs consisting of multiple Au nanocrystals can be formed over the entire seed particle surface. Finally, the SERS activity of these MSPNs is examined through the detection of rhodamine 6G and methylene blue. Of the different mesostructures, the bimetallic MSPNs have the highest sensitivity with the ability to detect 10^-7  m of rhodamine 6G and 10^-6  m of methylene blue. The properties of these MSPN particles, made using a novel synthetic process, make them excellent candidates for SERS-based chemical sensing applications.

Mechanobactericidal, Gold Nanostar Hydrogel-Based Bandage for Bacteria-Infected Skin Wound Healing

The emergence of multidrug resistant (MDR) microorganisms has led to the development of alternative approaches for providing relief from microbial attacks. The mechano-bactericidal action as a substitute for antimicrobials has become the focus of intensive research. In this work, nanostructure-conjugated hydrogel are explored as a flexible dressing against Staphylococcus aureus (S. aureus)-infected skin wounds. Herein gold nanostars (AuNst) with spike lengths reaching 120 nm are probed for antibacterial action. The bacterial killing of >95% is observed for Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli), while up to 60% for Gram-positive S. aureus. AuNst conjugated hydrogel (AuNst₁₂₀@H) reduced >80% colonies of P. aeruginosa and E. coli. In comparison, around 35.4% reduction of colonies are obtained for S. aureus. The viability assay confirmed the presence of about 85% of living NIH-3T3 cells when grown with hydrogels. An animal wound model is also developed to assess the efficiency of AuNst₁₂₀@H. A significant reduction in wound size is observed on the 10th day in AuNst₁₂₀@H treated animals with fully formed epidermal layers, hair follicles, new blood vessels, and arrector muscles. These findings suggest that novel dressing materials can be developed with antimicrobial nanotextured surfaces.

Facile Synthesis of Urchin-like Hollow Au Crystals for In Situ SERS Monitoring of Photocatalytic Reaction

Hollow urchin-like Au nanocrystals have been widely studied due to their excellent surface plasmon resonance properties and large specific surface area, but the controllable preparation of hollow urchin-like Au nanocrystals is still a challenge. In this article, we successfully prepared hollow urchin-like Au nanocrystals using HAuCl4·3H2O and AgNO3 as precursors and ascorbic acid as the reducing agent. No surface ligands or polymer stabilizers are required in the preparation process. HAuCl4·3H2O and AgNO3 will first form AgCl cubes, then the reducing agent, ascorbic acid, will reduce the Au3+ in the solution to Au0, and Au0 will be deposited on the pre-formed AgCl cubes to form AgCl@Au nanocrystals. We characterized the morphology of the prepared Au nanocrystals by scanning electron microscopy and found that by increasing the amount of HAuCl4·3H2O in the reaction, the surface morphology of the Au nanocrystals would change from a rough spherical shape to an urchin-like shape. By further increasing the amount of the precursor HAuCl4·3H2O, urchin-like Au will convert into flake-like morphology. The AgCl in the interior was removed with ammonia water, and finally, hollow urchin-like Au crystals were formed. In addition, we used R6G molecule to explore the surface-enhanced Raman spectroscopy (SERS) enhancement effect of prepared Au crystals. The results show that the minimum detectable concentration of R6G reaches 10−8 M. Moreover, we applied hollow urchin-like Au nanocrystals as catalysts and SERS enhancing materials to detect the photocatalytic reaction of 4-NTP. We used a 785 nm laser as both the SERS light source and the catalytic light source to monitor the photocatalytic effect of the laser on 4-NTP in situ by adjusting the laser power.

Surfactant-free Synthesis of Spiky Hollow Ag-Au Nanostars with Chemically Exposed Surfaces for Enhanced Catalysis and Single-Particle SERS

Spiky/hollow metal nanoparticles have applications across a broad range of fields. However, the current bottom-up methods for producing spiky/hollow metal nanoparticles rely heavily on the use of strongly adsorbing surfactant molecules, which is undesirable because these passivate the product particles' surfaces. Here we report a high-yield surfactant-free synthesis of spiky hollow Au-Ag nanostars (SHAANs). Each SHAAN is composed of >50 spikes attached to a hollow ca. 150 nm diameter cubic core, which makes SHAANs highly plasmonically and catalytically active. Moreover, the surfaces of SHAANs are chemically exposed, which gives them significantly enhanced functionality compared with their surfactant-capped counterparts, as demonstrated in surface-enhanced Raman spectroscopy (SERS) and catalysis. The chemical accessibility of the pristine SHAANs also allows the use of hydroxyethyl cellulose as a weakly bound stabilizing agent. This produces colloidal SHAANs that remain stable for >1 month while retaining the functionalities of the pristine particles and allows even single-particle SERS to be realized.

Bespoke nanostars: synthetic strategies, tactics, and uses of tailored branched gold nanoparticles

Interest in branched colloidal gold nanosystems has gained increased traction due to the structures' outstanding optical and plasmonic properties, resulting in utilization in techniques such as surface-enhanced spectroscopy and bioimaging, as well as plasmon photocatalysis and photothermal therapy. The unique morphologies of nanostars, multipods, urchins, and other highly branched nanomaterials exhibit selective optical and crystallographic features accessible by alterations in the respective wet-chemical syntheses, opening a vast array of useful applications. Examination of discriminatory reaction conditions, such as seeded growth (e.g., single-crystalline vs. multiply twinned seeds), underpotential deposition of Ag(i), galvanic replacement, and the dual use of competing reducing and capping agents, is shown to reveal conditions necessary for the genesis of assorted branched nanoscale gold frameworks. By observing diverse approaches, including template-directed, microwave-mediated, and aggregation-based methods, among others, a schema of synthetic pathways can be constructed to provide a guiding roadmap for obtaining the full range of desired branched gold nanocrystals. This review presents a comprehensive summary of such advances and these nuances of the underlying procedures, as well as offering mechanistic insights into the directed nanoscale growth. We conclude the review by discussing various applications for these fascinating nanomaterials, particularly surface-enhanced Raman spectroscopy, photothermal and photodynamic therapy, catalysis, drug delivery, and biosensing.

Hollow micro and nanostructures for therapeutic and imaging applications

Hollow particles have been extensively used in bioanalytical and biomedical applications for almost two decades due to their unique and tunable optoelectronic properties as well as their significantly high loading capacities. These intrinsic properties led them to be used in various bioimaging applications as contrast agents, controlled delivery (i.e. drugs, nucleic acids and other biomolecules) platforms and photon-triggered therapies (e.g. photothermal and photodynamic therapies). Since recent studies showed that imaging-guided targeted therapeutics have higher success rates, multimodal theranostic platforms (combination of one or more therapy and diagnosis modality) have been employed more often and hollow particles (i.e. nanoshells) have been one of the most efficient candidates to be used in multiple-purpose platforms, owing to their intrinsic properties that enable synergistic multimodal performance. In this review, recent advances in the applications of such hollow particles fabricated with various routes (either inorganic or organic based) were summarized to delineate strategies for tuning their properties for more efficient biomedical performance by overcoming common biological barriers. This review will pave the ways for expedited progress in design of next generation of hollow particles for clinical applications.

The morphology regulation and plasmonic spectral properties of Au@AuAg yolk-shell nanorods with controlled interior gap

Au@AuAg yolk-shell nanorods with tunable and uniform interior gap were synthesized through galvanic replacement reaction, where Au@Ag core-shell nanorods served as sacrificial templates and HAuCl₄ solution served as reductant. The effects of HAuCl₄, Ag shell thickness and aspect ratio (AR) of Au nanorods on the morphology of Au@AuAg yolk-shell nanorods had been investigated systemically. The results clearly indicated that AuAg alloy shell thickness of Au@AuAg yolk-shell nanorods could be increased from 3.6 to 10.0 nm by varying the amount of HAuCl₄. Meanwhile, the shape of AuAg alloy shell could be tuned by changing the shape of Ag coating. With the increasing of Ag coating thickness, the interior gap could be finely tuned in the range from 2.6 to 8.1 nm. The uniformity of interior gap could be improved by increasing the AR of Au nanorods. All these tunable geometries can further affect the plasmonic spectral properties of Au@AuAg yolk-shell nanorods. Because of the appearance of interior gap, the longitudinal localized surface plasmon resonance (LSPR) peak of Au@AuAg yolk-shell nanorods was located between that of bare Au nanorods and Au@Ag core-shell nanorods without interior gap. The increase of outer AuAg shell thickness can weaken the coupling between the inner and outer surface of the AuAg shell and lead to the decrease of AR, so the transverse and longitudinal LSPR bands gather together. The decrease of Ag coating thickness can enhance the coupling between inner Au nanorod and outer AuAg shell, which results in the red shift of the longitudinal LSPR band. This paper provides a method for studying the plasmonic coupling between two metal surfaces with a metal layer or a dielectric layer, which is also a new approach for regulating the plasmonic spectral properties of bimetallic nanoparticles. The controllability of Au@AuAg yolk-shell nanorods in both the interior gap and outer alloy shells makes them have potential applications in biomedicine, catalysis, nanoreactors, and energy storage.

Gold nanostars-diagnosis, bioimaging and biomedical applications

Gold Nanostars (GNS) have attracted tremendous attention toward themselves owing to their multi-branched structure and unique properties. These state of the art metallic nanoparticles possess intrinsic features like remarkable optical properties and exceptional physiochemical activities. These star-shaped gold nanoparticles can predominantly be utilized in biosensing, photothermal therapy, imaging, surface-enhanced Raman spectroscopy and target drug delivery applications due to their low toxicity and extraordinary optical features. In the current review, recent approaches in the matter of GNS in case of diagnosis, bioimaging and biomedical applications were summarized and reported. In this regard, first an overview about the structure and general properties of GNS were reported and thence detailed information regarding the diagnostic, bioimaging, photothermal therapy, and drug delivery applications of such novel nanomaterials were presented in detail. Summarized information clearly highlighting the superior capability of GNS as potential multi-functional materials for biomedical applications.

Precision control of the large-scale green synthesis of biodegradable gold nanodandelions as potential radiotheranostics

Herein, we report a new type of biodegradable, high surface-area gold nanodandelions (GNDs). This report possesses important features and some are the first of its kind: (1) the large scale green synthesis of GNDs with high monodispersity and a circa 100% yield with consistent chemistry, manufacturing and controls (CMC); (2) cellular/physiological degradability of GNDs leading to its disassembly into debris, which is indicative of the potential for possible body clearance; (3) precision control of the chemicophysical properties of the GNDs including shape, petal number and size, all can be judiciously fine-tuned by the synthetic parameters; (4) highly efficient radiotheranostics of GNDs encompassing better enhanced computed tomography (CT) contrast and pronounced X-ray induced reactive oxygen species (ROS) generation than conventional spherical gold nanoparticles (AuNP). It is noteworthy that the GNDs demonstrate a unique combinational effect of radiosensitization (production of superoxide anions and hydroxyl radicals) and type II photodynamic interaction (generation of singlet oxygen). Given the above, our reported GNDs are promising in clinical translation as radiotheranostics.

One-pot synthesis of hollow hydrangea Au nanoparticles as a dual catalyst with SERS activity for in situ monitoring of a reduction reaction

The controlled synthesis of metallic nanomaterials has attracted the interest of many researchers due to their shape-dependent physical and chemical properties. However, most of the synthesized nanocrystals cannot be combined with spectroscopy to measure the reaction kinetics, thus limiting their use in monitoring the catalytic reaction process to elucidate its mechanism. As a powerful analytical tool, surface-enhanced Raman spectroscopy (SERS) can be used to achieve in situ monitoring of catalytic reactions by developing bifunctional metal nanocrystals with both SERS and catalytic activities. Herein, we have developed a simple one-pot synthesis method for the large-scale and size-controllable preparation of highly rough hydrangea Au hollow nanoparticles. The growth mechanism of flower-like Au hollow nanostructures was also discussed. The hollow nanostructure with a 3D hierarchical flower shell combines the advantages of hollow nanostructure and hierarchical nanostructure, which possess high SERS activity and good catalytic activity simultaneously. Furthermore, the hydrangea Au hollow crystals were used as a bifunctional nanocatalyst for in situ monitoring of the reduction reaction of 4-nitrothiophenol to the 4-aminothiophenol.

Understanding the role of AgNO3 concentration and seed morphology in the achievement of tunable shape control in gold nanostars

Gold nanostars are one of the most fascinating anisotropic nanoparticles. The morphology of a nanostar can be controlled by changing various synthetic parameters; however, the detailed growth mechanism is still not fully understood. Herein, we investigate this process in six-branched nanostars, focusing first on the properties of a single crystalline seed, which evolves to include penta-twinned defects as the gateway to anisotropic growth into the 6-branched morphology. In particular, we report on a high-yield seed-mediated protocol for the synthesis of these particles with high dimensional monodispersity in the presence of Triton-X, ascorbic acid, and AgNO3. Detailed spectroscopic and microscopic analyses have allowed the identification of several key intermediates in the growth process, revealing that it proceeds via penta-twinned intermediate seeds. Importantly, we report the first experimental evidence tracking the location of silver with sub-nanometer resolution and prove its role as a stabilizing agent in these highly branched nanostructures. Our results indicate that metallic silver on the spikes stabilizes the nanostar morphology and the remaining silver, present when AgNO3 is added at a high concentration, deposits on the core and between the bases of neighboring spikes. Importantly, we also demonstrate the possibility of achieving dimensional monodispersity, reproducibility, and tunability in colloidal gold nanostars that are substantially higher than those previously reported, which could be leveraged to carry out holistic computational-experimental studies to understand, predict, and tailor their plasmonic response.

A gold nanoparticle system for the enhancement of radiotherapy and simultaneous monitoring of reactive-oxygen-species formation

Gold nanoparticles (AuNPs) are known to sensitize cancer cells to radiation therapy (RT) by increasing the deposition of ionizing energy in their immediate vicinity. However, this process of dose enhancement is challenging to monitor because it is heterogeneous at the sub-cellular scale. Furthermore, radiation damage is primarily mediated by reactive oxygen species (ROS) that are produced following water radiolysis. Here, radiation-responsive PEGylated gold nanoparticles (RPAuNPs) were synthesized for the enhanced generation and concurrent detection of ROS in cancer cells and tumors. PEGylated gold particles (20 nm diameter) were functionalized with dihydrorhodamine 123 (DHR-123), a known ROS sensor, to monitor ROS generation in their immediate vicinity. These NPs were able to effectively radiosensitize cells, as measured by increased cell apoptosis following RT. Furthermore, the fluorescence of these RPAuNPs was 7-fold higher after 6 Gy RT due to the local production of ROS near the surface of the NP. Finally, multispectral fluorescence imaging was used to monitor NP-induced ROS in vivo, following conformal RT, in a xenograft model of breast cancer. This theranostic NP system provides a novel approach for monitoring the nanoscale enhancement of RT by high-Z metal NPs.

Polydopamine@Gold Nanowaxberry Enabling Improved SERS Sensing of Pesticides, Pollutants, and Explosives in Complex Samples

Surface-enhanced Raman scattering (SERS) is a promising analysis technique for detecting various analytes in complex samples due to its unique vibrational fingerprints and high signal enhancement. However, impurity interference and substrate unreliability are direct suppression factors for practical application. Herein, we synthesize polydopamine@gold (PDA@Au) nanowaxberry, where Au nanoparticles are deposited on the surface of PDA sphere with high density and uniformity. Seed-mediated synthesis is used for fabrication of nanowaxberry. Au seeds are deposited on the surface of PDA sphere, then I ion coordinating ligand is employed to form stable AuI₄^- complex with AuCl₄^-, which decreases reduction potential of AuCl₄^- and avails formation of shell structure. Such nanowaxberry has high density of voids and gaps in three-dimensional space, which could absorb analytes and benefit practical SERS detection. Using malachite green as a model analyte, nanowaxberry realizes highly sensitive detection with low limit of detection (1 pM) and good reproducibility (relative standard deviation of about 10%). Meanwhile, the nanowaxberry is employed for practical detection of thiram, benzidine, and 2,4-dinitrotoluene in the environmental water, juice, apple peel, and soil. The high performance makes nanowaxberry to be potentially used for pesticides detection, pollutants monitoring, and forbidden explosives sensing in complex samples.

3D hierarchical Ag nanostructures formed on poly(acrylic acid) brushes grafted graphene oxide as promising SERS substrates

In this study, in situ generation of Ag nanostructures with various morphology on poly(acrylic acid) (PAA) brushes grafted onto graphene oxide (GO), for use as substrates for surface-enhanced Raman scattering (SERS), is demonstrated. The overall synthetic strategy involves the loading of Ag precursor ions ((Ag⁺ and [Ag(NH₃)₂]⁺) onto PAA brush-grafted GO, followed by their in situ reduction to Ag nanostructures of various morphology using a reducing agent (NaBH₄ or ascorbic acid). Novel 3D hierarchical flowerlike Ag nanostructures were obtained by using AgNO₃ as precursor and ascorbic acid as reducing agent. Using 4-aminothiophenol as probe molecules, the as-prepared hierarchical Ag nanostructures exhibited excellent SERS performance, providing enhancement factors of ∼10⁷.

Green synthesis of Au-Cu2-xSe heterodimer nanoparticles and their in-vitro cytotoxicity, photothermal assay

We demonstrate a new route for the synthesis of heterogeneous nanoparticles (NPs) composed of a gold domain (Au) and a heavily doped semiconductor domain (Cu_2-xSe) which exhibit a broad localized surface plasmon resonance (LSPR) arising from interactions between two nanocrystal domains. We also demonstrate the in-vitro cytotoxicity and photo thermal efficiency of as prepared Au-Cu_2-xSe heterodimer nanoparticles. This work establishes a new way of tuning LSPR by engineering the density of free charge carriers in two interacting domains.

Ligand Controlled Morphology Evolution of Active Intermediates for the Syntheses of Gold Nanostars

Gold nanostars have unique plasmonic properties that are related to the highly branched nanostructures. However, it is challenging to precisely control these branches. Here we studied the reaction kinetics on the seed-mediated growth process of gold nanostars using in situ UV-vis spectroscopy. The impact of hydroquinone ligands on the formation and evolution of active intermediates was systematically explored. In addition, we improved the classical seed-mediated method to achieve a much better control on the final morphology of gold nanostars by a sudden addition of a high concentration ligand solution. Our method can significantly advance the syntheses of gold nanostars and provide numerous opportunities to prepare nanomaterials with unique morphology and plasmonic properties.

Highly stable and biocompatible gold nanorod–DNA conjugates as NIR probes for ultrafast sequence-selective DNA melting

Colloidally stable and biocompatible DNA-functionalized Au nanorods are proved as NIR-addressable probes and mediators for ultrafast and sequence-selective DNA melting.

Simply controllable growth of single crystal plasmonic Au–Ag nano-spines with anisotropic multiple sites for highly sensitive and uniform surface-enhanced Raman scattering sensing

Simply synthesizing Au core@Au–Ag alloy spine nanostructures with a highly tunable LSPR band and dense “hot spots” for SERS sensing.

Growth of branched gold nanoparticles on solid surfaces and their use as surface-enhanced Raman scattering substrates

Branched gold nanoparticles were synthesized directly on solid surfaces (silicon, glass, ITO) in high yield. They revealed strong SERS activity for the detection of R6G with an enhancement factor estimated as greater than 8 orders of magnitude.