Noble Metal Nanoparticles Research Articles

Unveiling the Dual-Enhancing Mechanisms of Kinetically Controlled Silver Nanoparticles on Piezoelectric PVDF Nanofibers for Optimized SERS Performance.

Noble metal nanoparticle (NMP)-based composite substrates have garnered significant attention as a highly promising technique for surface-enhanced Raman scattering (SERS) in diverse scientific disciplines because their remarkable ability to amplify and functionalize Raman signals has positioned them as valuable tools for molecular detection. However, optimizing the size and distribution of NMPs has not received sufficient emphasis because of challenges associated with the precise control of deposition and the modulation of reducing rates during growth. In this research, we achieved the optimized size and spatial patterns of AgNWs on electrospun poly(vinylidene fluoride) (PVDF) nanofibers by utilizing a polydopamine (PDA) layer as a mild and controllable reduction mediator, by which the size and density of the AgNWs could be relatively precisely manipulated, achieving a dense distribution of effective "hot spots". On the other hand, harnessing the inherent piezoelectric properties of the electrospun PVDF nanofibers further boosted the LSPR effect during the SERS test, forming a flexible dual-enhancing composite SERS substrate with excellent sensitivity. In addition to addressing structural aspects, exploiting synergistic systems capable of transferring external energy or forces to enhance the SERS performances presents a compelling avenue to broaden the practical applications of SERS. The dual-enhanced substrate achieved an exceptional enhancement factor (EF) of 1.05 × 108 and a low detection limit (LOD) of 10-10 M during the SERS test. This study focuses on integrating NMPs with electrospun piezoelectric polymer nanofibers to develop a dual-enhancing SERS substrate with excellent sensitivity and practicality. The findings provide valuable insights into controllably depositing NMPs on electrospun polymer fibers and hold significant implications for the development of highly sensitive and practical SERS substrates across various applications.

Unveiling the Ultrafast Electron Transfer Dynamics in Epitaxial Dodecahedron CsPbBr3/Au Heterostructure

AbstractEpitaxial perovskite heterostructures consisting noble metal nanoparticles have been received immense interest in hot carrier photovoltaic devices and photocatalysis. The major understanding of carrier extraction across the interface of perovskite heterostructure have shown exciting interest for next generation device applications. In the present study, dodecahedron CsPbBr3/Au heterostructure was synthesized via hot injection method. From HR‐TEM images, we observed direct epitaxial growth between (110) plane of CsPbBr3 and (111) plane of Au nanoparticle (NPs), which was further supported by steady‐state and time‐resolved photoluminescence studies. Further, femtosecond transient absorption spectroscopy has been utilized to understand the charge transfer dynamics of synthesized samples. In CsPbBr3/Au heterostructure, faster recovery has been noticed than that of pristine CsPbBr3, which clearly suggests transfer of electrons from the conduction band of CsPbBr3 to Au NPs. The distinct fast electron transfer in the CsPbBr3/Au heterostructure can be mainly ascribed to the epitaxial growth and strong electronic coupling between CsPbBr3 and Au NPs. The reduced bleach intensity, faster bleach growth and recovery kinetics strongly suggest efficient electron transfer from CsPbBr3 NCs to Au NPs. These findings clearly establish that architecture of metal and perovskite heterostructures may pave way to develop suitable alternative for highly efficient photovoltaic devices and photocatalysis applications.

Fabrication of an Optoplasmonic Raft with Improved SERS Performance Detecting Methamphetamine through Bubble Enrichment.

In this work, a novel raft-like structure that combines noble metal nanoparticles (NPs) with an interconnected layer of hemispherical dielectric shell was fabricated and characterized. It was discovered that this hybrid material can enhance the optoplasmonic interaction between plasmonic and dielectric components, thereby improving the sensing performance in surface-enhanced Raman spectroscopy (SERS). Varied geometric parameters of the fabricated optoplasmonic raft, including the inner diameter and thickness of the dielectric shell, were attempted and analyzed through numerical simulation and experimental SERS measurements. With particular size, thickness, and incident orientation, the silica shell focuses the incident optical flow into the deposited silver NPs, undergoing similar near-field focusing behavior in comparison with other optoplasmonic entities. This optoplasmonic raft floating on the water surface is able to harvest the target molecules effectively through bubble enrichment, which rapidly captures and concentrates analytes from the aqueous phase. With a limited sampling time, the sensing performance of the developed optoplasmonic raft is improved by applying the optimized parameters involved in bubble enrichment. The substrates and corresponding enrichment method were implemented in the detection of methamphetamine (METH), achieving a limit of detection (LOD) down to 0.035 nM. As for practical onsite detection, the developed substrate and bubbling strategy were applied in an assembled set, employing a portable Raman spectrometer and an air pump. This set is able to detect METH dissolved in regular commercial beer, which is quite competent in the investigation of drug abuse.

Highly sensitive SERS platform using sub-10-nm Ag nanoparticles on GaN distributed Bragg reflector for detecting organic pollutants

Surface-enhanced Raman scattering (SERS) is crucial for the development of advanced detection technology and achieving high-sensitivity optical signals. Sub-10 nm noble metal nanostructures with high specific surface area and good catalytic activity are suitable for in-situ SERS analysis, while their SERS performance is inferior compared to larger noble metal nanoparticles with sizes of tens of nm. In this study, the weak SERS signals from sub-10 nm Ag nanoparticles (NPs) are greatly enhanced by developing a highly reflective multi-component system, in which monodisperse sub-10 nm Ag NPs are deposited onto a GaN-based distributed Bragg reflector (DBR). This Ag-NP/GaN DBR system exhibits remarkable SERS enhancement, approximately two orders of magnitude. This enhancement effect is further confirmed by SERS mapping over an area of 50 × 50 µm2. Moreover, the Ag-NP/GaN DBR system enables the in-situ monitoring of catalytic reaction processes of R6G and 4-NBT molecules, indicating high analytical sensitivity. To demonstrate practical applications, this Ag-NP/GaN DBR system is exploited to detect the toxic malachite green molecules and polyethylene microplastics, which show strong fingerprint signals. This work provides an effective solution to boost the weak SERS signals of sub-10 nm Ag NPs and paves the way towards practical applications.

One-Step Electrochemical Synthesis of Multiyolk-Shell Nanocoils for Exceptional Photocatalytic Performance.

Multiyolk-shell (mYS)nanostructures have garnered significant interest in various photocatalysis applications such as water splitting and waste treatment. Nonetheless, the complexity and rigorous conditions for the synthesis have hindered their widespread implementation. This study presents a one-step electrochemical strategy for synthesizing multiyolk-shell nanocoils (mYSNC), wherein multiple cores of noble metal nanoparticles, such as Au, are embedded within the hollow coil-shaped FePO4 shell structures, mitigating the challenges posed by conventional methods. By capitalizing on the dissimilar dissolution rates of bimetallic alloy nanocoils in an electrochemically programmed solution, nanocoils of different shapes and materials, including two variations of mYSNCs are successfully fabricated. The resulting Au-FePO4 mYSNCs exhibit exceptional photocatalytic performance for environmental remediation, demonstrating up to 99% degradation of methylene blue molecules within 50min and 95% degradation of tetracycline within 100min under ultraviolet-visible (UV-vis) light source. This remarkable performance can be attributed to the abundant electrochemical active sites, internal voids facilitating efficient light harvesting with coil morphology, amplified localized surface plasmon resonance (LSPR) at the plasmonic nanoparticle-semiconductor interface, and effective band engineering. The innovative approach utilizing bimetallic alloys demonstrates precise geometric control and design of intricate multicomponent hybrid composites, showcasing the potential for developing versatile hollow nanomaterials for catalytic applications.

Spontaneous Formation of Ultrasmall Noble Metal Nanoparticles on Cobalt-Based Layered Double Hydroxide for Electrochemical and Environmental Catalysis.

Supported noble metal nanoparticles (NMNPs) are appealing for energy and environment catalysis. To facilitate the loading of NMNPs, in situ reduction of Mn+ on the support with extra reductants/surfactants is adopted, but typically results in aggregated NMNPs with uneven size distributions or blocked active sites of the NMNPs. Herein, the use of cobalt layered double hydroxide (Co-LDH) is proposed as both support and reductant for the preparation of supported NMNPs with ultrasmall sizes and even distributions. The resultant Co-LDH-supported NMNPs exhibit excellent catalytic performance and stability. For example, Ir/Co-LDH displays a low overpotential of 188mV (10mAcm-2) for electrocatalytic oxygen evolution reaction and a long-term stability over 100h (100mAcm-2) in overall water splitting. Ru/Co-LDH can achieve a 4-nitrophenol reduction with high rate of 0.36min-1 and S2- detection with low limit of detection (LOD) of 0.34µm. Overall, this work provides a green and effective strategy to fabricate supported NMNPs with greatly improved catalytic performances.

A colorimetric and SERS dual-mode aptasensor for the detection of Shiga toxin type II based on Mn/Fe-MIL(53)@AuNSs

Shiga toxin type II (Stx2), the major virulence component of enterohemorrhagic Escherichia coli, is strongly associated with the life-threatening hemolytic uremic syndrome thus posing a substantial risk to food safety and human health. In this work, a dual-mode aptasensor with colorimetric and surface-enhanced Raman scattering was developed for Stx2 specific detection based on noble metal nanoparticles and Raman reporter loaded metal-organic framework (Mn/Fe-MIL(53)@AuNSs-MBA). The Mn/Fe-MIL(53)@AuNSs could catalyze the H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), thereby enabling visual detection. Meanwhile, the SERS signal from MBA can be enhanced by the decorated AuNSs. Under optimal conditions, a linear range of 0.05–500 ng/mL with limit of detection (LOD) of 26 pg/mL was achieved in colorimetric mode and a linear range of 5–1000 ng/mL with LOD of 0.82 ng/mL in SERS mode, in which the dual-mode results complement each other, widening the linear range, increasing the accuracy and reliability of the detection. The method was further applied to the detection of Stx2 in milk with average recovery of 101.1 %, demonstrating its superior potential for bacterial toxin monitoring.

Advances in the preparation and biological applications of core@shell nanocrystals based on quantum dots and noble metal.

Core/shell structured nanoparticles (NPs) are a novel category of functional materials that have garnered widespread attention due to their advantageous preparation methods, unique characteristics, and multifunctional application prospects, which have shown significant performance in materials chemistry and many other fields, such as electronics, biomedical, pharmaceutical, optics, and catalysis. Although some reviews about core/shell NPs have been published, there is still an intense requirement for an extensive review about the updated literature and new reported core/shell nanomaterials. Colloidal quantum dots (QDs) and noble metal NPs have a very small size, which results in the large surface-to-volume ratio and under-coordinated chemical bonds. As a result, the effort on the design of core-shell structure has been essential for colloidal QDs and noble metal NPs. In this review, the core-shell structures dominated by traditional QDs and CsPbX3 perovskite QDs, as well as noble metal nanocrystals (NCs) were summarized. The applications of the above core-shell structure NCs in medical or biological fields such as sensing, biological imaging, medical diagnostics and therapeutics, immunological diagnosis were discussed. The main objective of this review is to provide a better basis for the synthesis, properties, and biomedical applications of QDs or noble metal core/shell NPs, which is beneficial for the further development of QDs, noble metal NPs, and other NPs.

Nanorod structure tuning and defect engineering of MoOx for high-performance SERS substrates.

In recent years, surface-enhanced Raman scattering (SERS) based on metal oxide semiconductors has been an active area of research and development, attracting significant scientific interest. These SERS substrates are known as plasmon-free SERS substrates because they are not based on noble metal nanoparticles but mainly on the defects, structure, and surface morphology of semiconductors to enhance the Raman signal. In this study, we fabricated a SERS substrate based on molybdenum oxide, using reactive DC magnetron sputtering and then used different simple and effective strategies to enhance the Raman signal. The results show that nanorod structure, oxygen deficiency engineering, phase engineering, and optical properties can be easily controlled by varying sputtering time and annealing time of MoOx SERS substrates. The analysis methods XRD, PL, and Raman show that with the optimal fabricated conditions. The presence of oxygen defects and a mixed MoO3, Mo9O26 phase structure in as well as the nanorod structure of MoOx SERS substrates could likely enhance Raman signals via a chemical mechanism (CM) and electromagnetic mechanism (EM). The MoOx SERS substrates were also used to detect R6G at low concentrations, with an EF of 1.14 × 106 (at 0.01 ppm), LOD of 0.01 ppm, and good temporal stability and reproducibility.

Utilization of Green Synthesis for Eco-Friendly Nanomaterials and Their Advanced Biomedical Applications in Noble Metal Nanoparticles

Nanoparticles, the foundation of nano-science and nanotechnology, possess significant power and functionality across various fields. These nanoparticles are typically created through physical or chemical processes, but concerns surrounding toxicity have been raised. This discussion explores several environmentally friendly and low-toxicity green synthesis methods as alternatives. Many nanomaterials have been created and effectively applied in a variety of applications as nanotechnology has advanced. It is still difficult to create nanomaterials with appropriate functional characteristics, particularly for biomedical uses. Currently, a significant amount of the nanomaterials created for these uses are heavily dependent on non-renewable resources and energy-intensive manufacturing techniques. Furthermore, the long-term impacts of these unsustainable nanomaterials on human health, the environment, and climate change lag behind the exponential development in their innovation and discovery. A sustainable nanomaterial design that uses natural and renewable resources and has the least negative effects on society is therefore desperately needed. Green synthesis, which employs plant extracts rather than synthetic chemical agents to lower metal ions, was created as a solution to these problems. Because green synthesis is less expensive, produces less pollution, and enhances the safety of the environment and human health, it is preferable to traditional chemical synthesis. This review assessed recent advancements in the environmentally friendly synthesis of silver (Ag NPs) and gold (Au NPs) nanoparticles. Green synthesis, on the other hand, offers different development opportunities and possible applications in light of the present environmental issues and pollution linked to chemical synthesis.

Highly dispersed noble metal nanoparticle composites on biomass-derived carbon-based carriers: synthesis, characterization, and catalytic applications.

Precious metal nanoparticles have been widely investigated due to their excellent activity shown in catalysis and sensing. However, how to prepare highly dispersed noble metal nanoparticles to improve the lifetime of catalysts and reduce the cost is still an urgent problem to be solved. In this study, a carbon-based carrier material was prepared by an expansion method and loaded with Pd or Ag nanoparticles on this carbon material to synthesize precious metal nanoparticle composites, which were characterized in detail. The results show that the nanoparticles prepared using this method exhibit superior dispersion. Under the synergistic effect of noble metal nanoparticles and porous carbon carriers, the composites exhibited excellent catalytic degradation of p-nitrophenol and showed excellent sensing performance in the modified hydrogen peroxide sensor electrode. This approach is highly informative for the preparation of nanocomposites in medical and environmental fields.

SERS detection of dopamine using metal-chelated Ag nanoshell.

As the concentrations of different neurotransmitters can indicate the presence of certain disorders affecting brain functions, quantitative analyses of neurotransmitters have attracted increasing attention in various fields. Surface-enhanced Raman scattering (SERS) spectroscopy is an outstanding spectroscopic analytical tool that enables detection at the single molecule level with high specificity. As local field enhancement of surface plasmon is effective within nanometers, active interaction between SERS-active noble metals (gold and silver) and analyte molecules enhances the molecular detection capacity of SERS. However, neurotransmitters and noble metal nanoparticles are often not affinitive, because neurotransmitters generally have a hydroxyl group rather than a thiol group. As a result, the interaction between the two typically remains inactive, which makes detection more difficult. To overcome this limitation, in the present work we utilized metal-chelation to attract dopamine, a neurotransmitter molecule, close to the surface of silver nanoparticles. AgNS was capped with poly(vinyl alcohol) (PVA) and sequentially integrated with copper ion to bind dopamine in the form of chelate bonding between dopamine and copper. The PVA linked AgNS and metal ions through a coordinate bond between hydroxyl groups and metal ions. This metal-chelation-functionalized nanoprobe allowed us to stably detect dopamine in aqueous solution at a concentration of less than 10-6 M. Therefore, this method provides a convenient and easy-to-prepare option for the effective detection of dopamine, thus meaning it has the potential to be applied to other neurotransmitters.

ОБҐРУНТУВАННЯ ПАРАМЕТРІВ МЕТОДУ РОЗРАХУНКУ ХАРАКТЕРИСТИК ЕЛЕКТРОМАГНІТНОГО РОЗСІЮВАННЯ МЕТАЛЕВОЇ НАНОЧАСТИНКИ У ОПТИЧНОМУ ДІАПАЗОНІ

Structures of nanoparticles of noble metals in the optical range are of great interest in solving practical problems of building and using optical antennas and sensors for communication, creating solar cells, coatings for masking objects in the optical range and their detection. Currently, intensive research is being carried out on resonance effects during the scattering and absorption of light by such nanosized particles. There are both experimental methods of studying the characteristics of electromagnetic scattering of nanostructures in the optical range, and methods of mathematical modeling. Mathematical methods are subject to strict requirements regarding accuracy and ensuring the convergence of calculation results. The method of integral equations is widely used to model scattering from various objects with finite dielectric constants. At the same time, in the optical range, scattering on nanoparticles, as homogeneous resonant objects, has its own characteristics that affect the accuracy and convergence of the calculation algorithm. The article examines the issue of choosing and justifying the parameters of the method for calculating the characteristics of electromagnetic scattering of nanoparticles of noble metals of different sizes in the optical range, which are based on the application of a system of Müller integral equations. The internal convergence of the algorithm for calculating electromagnetic scattering characteristics depends on the size and shape of nanoparticles. When calculating according to the proposed numerical method, the number of nodes in which the current density was calculated was chosen in such a way that there was an internal convergence of the algorithm characterized by a given value . The required number of current nodes and the discretization step on the surface of one nanoparticle of two sizes (75x75x25 and 100x100x20) were obtained, which ensure internal convergence and the best accuracy of the proposed computational algorithm. Nanoparticles of these sizes will be used as the basis for the construction of various structures. The direction of further research is obtaining and analyzing the characteristics of electromagnetic scattering of various structures made of silver nanoparticles under different conditions of irradiation and polarization of the incident electromagnetic wave.

Full-spectrum plasmonic semiconductors for photocatalysis.

Localized surface plasmon resonance (LSPR) of noble metal nanoparticles can focus surrounding light onto the particle surface to boost photochemical reactions and solar energy utilization. However, the rarity and high cost of noble metals limit their applications in plasmonic photocatalysis, forcing researchers to seek low-cost alternatives. Recently, some heavily doped semiconductors with high free carrier density have garnered attention due to their metal-like LSPR properties. However, plasmonic semiconductors have complex surface structures characterized by the presence of a depletion layer, which poses challenges for active site exposure and hot carrier transfer, resulting in low photocatalytic activity. In this review, we introduce the essential characteristics and types, synthesis methods, and characterization techniques of full-spectrum plasmonic semiconductors, elucidate the mechanism of full-spectrum nonmetallic plasmonic photocatalysis, including the local electromagnetic field, hot carrier generation and transfer, the photothermal effect, and the solutions for the surface depletion layer, and summarize the applications of plasmonic semiconductors in photocatalytic environmental remediation, CO2 reduction, H2 generation, and organic transformations. Finally, we provide a perspective on full-spectrum plasmonic photocatalysis, aiming to guide the design and development of plasmonic photocatalysts.

ISERS: from nanotag design to protein assays and ex vivo imaging.

Proteins are an eminently important class of ubiquitous biomacromolecules with diverse biological functions, and numerous techniques for their detection, quantification, and localisation have been developed. Many of these methods exploit the selectivity arising from molecular recognition of proteins/antigens by immunoglobulins. The combination of surface-enhanced Raman scattering (SERS) with such "immuno"-techniques to immuno-SERS (iSERS) is the central topic of this review, which is focused on colloidal SERS nanotags, i.e., molecularly functionalised noble metal nanoparticles conjugated to antibodies, for their use in protein assays and ex vivo imaging. After contrasting the fundamental differences between label-free SERS and iSERS, including a balanced description of the advantages and drawbacks of the latter, we describe the usual workflow of iSERS experiments. Milestones in the development of the iSERS technology are summarised from a historical perspective. By highlighting selected examples from the literature, we illustrate the conceptual progress that has been achieved in the fields of iSERS-based protein assays and ex vivo imaging. Finally, we attempt to predict what is necessary to fully exploit the transformative potential of the iSERS technology by stimulating the transition from research in academic labs into applications for the benefit of our society.

Thermally stable Pd/CeO2@SiO2 with a core-shell structure for catalytic lean methane combustion.

Noble metal catalysts exhibit high catalytic activity in lean CH4 combustion at low temperatures. However, the high surface energy of noble metal nanoparticles makes them susceptible to deactivation due to migratory-aggregation during the catalytic process. Herein, a core-shell structure with a Pd/CeO2 core and a SiO2 shell (denoted as Pd/CeO2@SiO2) was designed and prepared to enhance the thermal stability for catalytic lean CH4 combustion. A series of characterization methods demonstrated the successful encapsulation of SiO2 and the modified thermal stability. The results of activity tests indicated that Pd/CeO2@SiO2 exhibited the optimal catalytic performance. After seven runs, Pd/CeO2@SiO2 achieved 90% conversion of CH4 at 385 °C compared to Pd/CeO2 at 440 °C. The remarkable catalytic performance was attributed to the synergistic effect of strengthened metal-support interactions and the core-shell structure. On the one hand, the migration and aggregation of Pd nanoparticles were limited due to the protection of the SiO2 shell layer. On the other hand, the SiO2 shell layer further enhanced the interactions between the Pd nanoparticles and CeO2, thus promoting the formation of PdxCe1-xO2-δ solid solutions and active oxygen species, which were beneficial for the improvement of the stability and redox capacity of the catalyst.

Metallic nanostructure-based aptasensors for robust detection of proteins.

There is a significant need for fast, cost-effective, and highly sensitive protein target detection, particularly in the fields of food, environmental monitoring, and healthcare. The integration of high-affinity aptamers with metal-based nanomaterials has played a crucial role in advancing the development of innovative aptasensors tailored for the precise detection of specific proteins. Aptamers offer several advantages over commonly used molecular recognition methods, such as antibodies. Recently, a variety of metal-based aptasensors have been established. These metallic nanomaterials encompass noble metal nanoparticles, metal oxides, metal-carbon nanotubes, carbon quantum dots, graphene-conjugated metallic nanostructures, as well as their nanocomposites, metal-organic frameworks (MOFs), and MXenes. In general, these materials provide enhanced sensitivity through signal amplification and transduction mechanisms. This review primarily focuses on the advancement of aptasensors based on metallic materials for the highly sensitive detection of protein targets, including enzymes and growth factors. Additionally, it sheds light on the challenges encountered in this field and outlines future prospects. We firmly believe that this review will offer a comprehensive overview and fresh insights into metallic nanomaterials-based aptasensors and their capabilities, paving the way for the development of innovative point-of-care (POC) diagnostic devices.

Self-assembly of hard anions around cationic gold nanorods: potential structures for SERS.

The placement of polyoxometalates next to the surface of noble metallic nanoparticles has been found to enhance the surface-enhanced Raman scattering (SERS) effect. The enhancement is believed to stem from either charge (electrostatic attraction) or chemical effects. Anisotropic gold nanorods are recognized as useful nanostructures for SERS, mainly due to the high electric field enhancement at their ends. The presented work examines the use of a polyoxometalate encapsulated gold nanorod for SERS, to assess whether the two enhancement pathways would be synergetic. For this, a gold nanorod-polyoxometalate composite was synthesized by coating cetyltrimethylammonium bromide-stabilized gold nanorods with a silicotungstic Keggin anion through electrostatic attraction. The structure was characterized, confirming that the nanorods have been fully encapsulated by the polyoxometalate. The SERS performance of the composite was assessed in solution using crystal violet as a SERS indicator, finding an analytical enhancement factor of 1.8 × 104 in colloidal solution. The enhancement mechanism was examined first by comparison to gold nanorods stabilized by a cetyltriethylammonium bromide bilayer, cationic thiol bound polyoxometalate, and polyelectrolyte coating. Next, composites made using polyoxometalates of different atomic composition and charge were examined. It was concluded that the polyoxometalate charge had a noticeable effect on the enhancement while the atomic composition did not. Furthermore, high enhancement is observed mainly in cases where the nanorod monolayer allows the sequestration of the dye molecule into the nanoparticle's ligand layer. The proposed mechanism therefore involves the negative charge of the polyoxometalate attracting the positively charged dye, and facilitating the sequestration of the dye within the ligand bilayer, closer to the nanorod's surface.

Two-color interferometric scattering (iSCAT) microscopy reveals structural dynamics in discrete plasmonic molecules.

Plasmonic molecules are discrete assemblies of noble metal nanoparticles (NPs) that are of interest as transducers in optical nanosensors. So far, NPs with diameters of ∼40 nm have been the preferred building blocks for plasmonic molecules intended as optical single molecule sensors due to difficulties associated with detecting smaller NPs through elastic scattering in conventional darkfield microscopy. Here, we apply 405 nm, 445 nm two-color interferometric scattering (iSCAT) microscopy to characterize polyethylene glycol (PEG) tethered dimers of 10 nm and 20 nm Ag NPs and their monomers. Dimers of both NP sizes can be discerned from their respective monomers through changes in the average iSCAT contrast. In the case of 20 nm Ag NPs, dimer formation induces a change in the sign of the iSCAT contrast, providing a characteristic signal for detecting binding events. 20 nm Ag NP dimers with 0.4 kDa and 3.4 kDa polyethylene glycol (PEG) spacers show iSCAT contrast distributions with significantly different averages on both wavelength channels. The iSCAT contrast measured for individual PEG-tethered 10 nm or 20 nm NP dimers as a function of time shows contrast fluctuations indicative of a rich structural dynamics in the assembled plasmonic molecules, which provides an additional metric to discern dimers from monomers and paves the path to a new class of interferometric plasmon rulers.

A universal strategy for green and surfactant-free synthesis of noble metal nanoparticles.

We propose a universal, green, and surfactant-free strategy to synthesize noble metal particles with high monodispersity using gaseous H2 as a reducing agent in a solution at 60 °C. The prepared Pt nanoparticles have a 24 mV more positive half-wave potential than the commercially available Pt/C in the oxygen reduction reaction, while showing high durability with negligible half-wave potential decay after 10 000 cycles of testing.