Raman Scattering Activity Research Articles

Development of Au Nanoparticle Two-Dimensional Assemblies Dispersed with Au Nanoparticle-Nanostar Complexes and Surface-Enhanced Raman Scattering Activity.

We recently found that polyvinylpyrrolidone (PVP)-protected metal nanoparticles dispersed in water/butanol mixture spontaneously float to the air/water interface and form two-dimensional assemblies due to classical surface excess theory and Rayleigh-Bénard-Marangoni convection induced by butanol evaporation. In this study, we found that by leveraging this principle, a unique structure is formed where hetero gold nanospheres (AuNPs)/gold nanostars (AuNSs) complexes are dispersed within AuNP two-dimensional assemblies, obtained from a mixture of polyvinylpyrrolidone-protected AuNPs and AuNSs that interact electrostatically with the AuNPs. These structures were believed to form as a result of AuNPs/AuNSs complexes formed in the water/butanol mixture floating to the air/water interface and being incorporated into the growth of AuNP two-dimensional assemblies. These structures were obtained by optimizing the amount of mixed AuNSs, with excessive addition resulting in the formation of random three-dimensional network structures. The AuNP assemblies dispersed with AuNPs/AuNSs complexes exhibited significantly higher Raman (surface-enhanced resonance Raman scattering: SERRS) activity compared to simple AuNP assemblies, while the three-dimensional network structure did not show significant SERRS activity enhancement. These results demonstrate the excellent SERRS activity of AuNP two-dimensional assemblies dispersed with hetero AuNPs/AuNSs complexes.

Chemically Engineered Sulfur Vacancies on Few-Layered Molybdenum Disulfide Nanosheets for Remarkable Surface-Enhanced Raman Scattering Activity

In recent years, molybdenum disulfide nanosheets (MoS2 NSs) with sulfur surface defects have been used for surface-enhanced Raman scattering (SERS). However, methods to generate sulfur defects on the MoS2 NS surface are sophisticated and expensive. In this study, we present a relatively straightforward approach to quickly creating sulfur defects on MoS2 NSs by chemical treatment with NaBH4. Few-layered MoS2 NSs (FL-MoS2 NSs) were formed by exfoliating bulk-MoS2 in isopropanol. By oxidation–reduction reactions of FL-MoS2 NSs mixed with a suitable concentration of NaBH4, the resulting MoS2 NSs with abundant sulfur defects (SV-FL-MoS2 NSs) can be obtained. Spectroscopic and electron microscopic methods are used to demonstrate sulfur defects in SV-FL-MoS2 NSs. Rhodamine (R6G) and rhodamine-B (RhB) were used as Raman analytes to evaluate the SERS efficiency of SV-FL-MoS2 NSs. The developed SERS substrate provided detection limits of 1 × 10–8 M for both R6G and RhB, with enhancement factors of 2.21 × 106 and 4.02 × 106, respectively. Our measurements of SV-FL-MoS2 NSs’ energy band gap and R6G/RhB confirmed that charge transfer (CT) and tight molecular contacts are responsible for their excellent SERS sensitivity. With the development of new, low-cost semiconductor-based SERS materials, this discovery could impact materials science and biosensing platforms.

Tunable photochemical deposition of silver nanostructures on layered ferroelectric CuInP2S6

Two-dimensional layered ferroelectric materials, such as CuInP2S6 (CIPS), are promising candidates for novel and high-performance photocatalysts, owing to their ultrathin layer thickness, strong interlayer coupling, and intrinsic spontaneous polarization, while how to control the photocatalytic activity in layered CIPS remains unexplored. In this work, we report for the first time, the photocatalytic activity of ferroelectric CIPS for the chemical deposition of silver nanostructures (AgNSs). The results show that the shape and spatial distribution of AgNSs on CIPS are tunable by controlling layer thickness, environmental temperature, and light wavelength. The ferroelectric polarization in CIPS plays a critical role in tunable AgNS photodeposition, as evidenced by layer thickness and temperature dependence experiments. We further reveal that AgNS photodeposition process starts from active site creation, selective nanoparticle nucleation/aggregation, to continuous film formation. Moreover, AgNS/CIPS heterostructures prepared by photodeposition exhibit excellent resistance switching behavior and good surface enhancement Raman Scattering activity. Our findings provide new insight into the photocatalytic activity of layered ferroelectrics and offer a new material platform for advanced functional device applications in smart memristors and enhanced chemical sensors.

Study of Charge Transfer Contribution to Surface-Enhanced Raman Scattering Activity of Cu\(_2\)O Nano-octahedral Substrate

In this study, a surface-enhanced Raman scattering (SERS) substrate based on an octahedral cuprous oxide (Cu2O) nanostructure to probe methylene blue (MB) molecules as an analyte chemical has been implemented. Octahedral Cu2O nanocrystals were synthesized by a novel hydrothermal process using only ethylene glycol as both a reductant and organic solvent. The characteristics of Cu2O nanocrystals were well recognized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), FTIR, and Raman spectroscopy. The mechanism of the SERS surface has been thoroughly investigated and has been shown to involve the contributions of both surface plasmon resonance and charge transfer effects. Using a simple collection rule for SERS bands, the portion of charge transfer processes was estimated to be about 46%.

Abnormally Weak Surface-Enhanced Raman Scattering Activity of Tip-Rich Au Nanostars: The Role of Interfacial Defects.

Designing and regulating the geometry of a given plasmonic metal (Au, Ag, etc.) has become one of the most efficient approaches to achieve highly active surface-enhanced Raman spectroscopy (SERS) substrates, but this work demonstrates that plain efforts on this may not be enough. Here, we report that the often-neglected inner crystal defects also have huge impacts on the SERS activity, through a case of Au nanostars (NSs) with good SERS geometry but rich in defects. The results suggest that the interfacial defects (twin boundaries and superlattices) in the NSs aggravate the electronic oscillation damping via reducing the free path of electron scattering. This eventually results in weak local electromagnetic fields near the NS surfaces (or weak SERS activity of the NSs). This study has demonstrated the huge impact of interfacial defects on SERS activity and thus has a significant guideline for the design and fabrication of efficient SERS substrates.

Development of Effectual Substrates for SERS by Nanostructures-on flexible surfaces

The current study examines recent advancements in surface-enhanced Raman scattering (SERS), a technique that employs flexible surfaces as an active substrate, this surfaces consist from two-dimensional thermo-plasmonic grating. With 53 nm Au layer (was deposited on the 2D grating structure of the PDMS by the PVD method). The explosive wire technique was used to preparing Ag nanoparticles that were used for the purpose of SERS. The effect of the plasmonic nanostructures on the absorption spectra and Surface - Enhanced Raman Scattering (SERS) activities was examined. Rhodamine 6G dye was used as a probe molecule. X-Ray diffraction (XRD) was used to examine the structural characteristics of the nanoparticles. The morphology was assessed using Field Emission Scanning Electron Microscopy(FESEM). A twin beam UV-Vis Spectrophotometer was used to measure the absorption of the combined Rh6G dye (concentration 1×10“–6M) with the nanostructures. a Sunshine Raman microscope system and a 50mm objective lens, used for investigating the Raman spectra of the Rh6G combined with nanostructures. The results showed that the enhancement factor (EF) for SERS of R6G (1×M) reached to (2.2×10 3) When using Ag nanoparticles and (0.08 × 103) when R6G deposited directly on the flexible substrates without nanostructures at the wave number (1650 cm−1), we produced a recyclable, homogeneous, and highly sensitive SERS substrate with dependable reproducibility. For the SERS substrate, a surface made up of two-dimensional (2D) flexible grating substrates was chosen to provide multiple modalities in electrical and medicinal applications.

Enhanced Surface-Enhanced Raman Scattering Activity of MoS2–Ag-Reduced Graphene Oxide: Structure-Mediated Excitonic Transition

Enhanced Surface-Enhanced Raman Scattering Activity of MoS₂–Ag-Reduced Graphene Oxide: Structure-Mediated Excitonic Transition

Surface-Enhanced Raman Scattering Activity of ZrO2 Nanoparticles: Effect of Tetragonal and Monoclinic Phases.

The effect of the ZrO2 crystal form on surface-enhanced Raman scattering (SERS) activity was studied. The ratio of the tetragonal (T) and monoclinic (M) phases of ZrO2 nanoparticles (ZrO2 NPs) was controlled by regulating the ratio of two types of additives in the hydrothermal synthesis method. The SERS intensity of 4-mercaptobenzoic acid (4–MBA) was gradually enhanced by changing the M and T phase ratio in ZrO2 NPs. The degree of charge transfer (CT) in the enhanced 4–MBA molecule was greater than 0.5, indicating that CT was the main contributor to SERS. The intensity of SERS was strongest when the ratio of the T crystal phase in ZrO2 was 99.7%, and the enhancement factor reached 2.21 × 104. More importantly, the proposed study indicated that the T and M phases of the ZrO2 NPs affected the SERS enhancement. This study provides a new approach for developing high-quality SERS substrates and improving the transmission efficiency of molecular sensors.

Application of Delafossite AgFeO2 Nanoparticles as SERS Substrate and Antimicrobial Agent

AbstractWe have used simple chemical route to synthesize delafossite silver ferrite (AgFeO2) nanoparticles (NPs). AgFeO2 NPs were utilized as Raman substrate for detection of Rhodamine 6G (R6G) molecules. AgFeO2 NPs substrate show excellent Surface‐enhanced Raman Scattering (SERS) activity, which enables ultrasensitive detection of R6G with a concentration down to 1 picomolar (1 pM) with an enhancement factor (EF) of 1.6×1010. The observed SERS signal enhancement in this AgFeO2 NPs system is attributed to a combination of electromagnetic (EM) enhancement, charge ‐ transfer (CT) effect between R6G analyte molecules and AgFeO2 NPs surface and Resonance Raman (RR) effect. Further, AgFeO2 NPs were used to study its antibacterial activity against certain different pathogenic bacteria. The antibacterial studies showed that the AgFeO2 NPs possesses potential inhibitory effect against both Gram‐negative and Gram‐positive bacteria. In addition, AgFeO2 NPs was found cytotoxic to yeast cells. The stable aqueous colloids of AgFeO2 NPs may find potential applications in the biomedical field as a sensing platform for the trace level detection of analyte molecules and antimicrobial agent.

Signature of Plasmonic Nanostructures Synthesised by Electrical Exploding Wire Technique on Surface-Enhanced Raman Scattering

This work aims to fabricate two types of plasmonic nanostructures by electrical exploding wire (EEW) technique and study the effects of the different morphologies of these nanostructures on the absorption spectra and Surface-Enhanced Raman Scattering (SERS) activities, using Rhodamine 6G as a probe molecule. The structural properties of these nanostructures were examined using X-Ray diffraction (XRD). The morphological properties were examined using field emission scanning electron microscopy (FESEM) and scanning transmission electron microscopy (STEM). The absorption spectra of the mixed R6G laser dye (concentration 1×10-6 M) with prepared nanostructures were examined by double beam UV-Vis Spectrophotometer. The Raman spectra of the R6G mixed with the prepared nanostructures were examined using a Horiba HR Evolution 800 Raman microscope system with an objective lens (50 ×). The FESEM and STEM images indicated that the Ag nanoparticles (AgNPs) with 35 nm average particle sizes were decorated on the surface of the AgNWs and the PDA layer by EEW technique, forming AgNW@AgNPs and AgNW@PDA@AgNPs nanostructures. The results indicated that the increased intensities of the absorption spectra peaks and the SERS arise from the hot spots and the roughness of the surface of nanostructures. The SERS enhancement factor of R6G (1×10-6 M) was reached at 2.3×107 and 2.5×107, at the wave number of 1650 cm-1, for the AgNW@AgNPs and AgNW@PDA@AgNPs nanostructures, respectively, after being excited by (λexc. = 532 nm) laser source. It can be concluded that the AgNW@AgNPs and AgNW@PDA@AgNPs nanostructures were fabricated with an easy and simple way without the need for additional chemical compounds. These nanostructures attained a reliable and sensitive detection and can be utilized in a variety of SERS applications, such as chemical and biological sensors.

On-Site and Quantitative Detection of Trace Methamphetamine in Urine/Serum Samples with a Surface-Enhanced Raman Scattering-Active Microcavity and Rapid Pretreatment Device.

Here, it reports a high-throughput detection method for reliably quantitative analysis of illegal drugs in complex biological samples by means of a surface-enhanced Raman scattering (SERS) active microcavity and rapid pretreatment device. Based on the well-made hemispherical microcavities that regularly distributed on a glass array, the quality-controllable microcavity device is fabricated by the compact self-assembly of core-shell nanopeanuts (CSNPs) onto the inside surface. Both the CSNPs with a quantifiable internal standard signal of crystal violet acetate anchored inside their gap and the well-made microcavity referred to the physical amplification of the microscale groove surface will do well in trace analysis, which will allow us to realize the accurately quantitative SERS analysis of targeted analytes spread on the bottom area of the microcavity array. As an example, 0.8 nM malachite green and 160 ppb methamphetamine (MATM) have been successively detected in a wide range as standard, while even 0.01 ppm MATM mixed in the urine/serum samples has been efficiently tested by the microcavity device equipped with a rapid pretreatment device (manual monolithic column syringe needle). All of the above suggest that the SERS-active microcavity equipped with a rapid pretreatment device has potential in the on-site quick test of trace amounts of illegal drugs in bodily fluid samples or other field analysis of food sanitation, environmental safety, and public health.

Bioinspired One-Step Synthesis of Pomegranate-like Silica@Gold Nanoparticles with Surface-Enhanced Raman Scattering Activity.

Gold-silica (Au-SiO2) nanohybrids are of great technological importance, and it is crucial to develop facile synthetic protocols to prepare Au-SiO2 nanohybrids with novel structures. Here we report the bioinspired synthesis of pomegranate-like SiO2@Au nanoparticles (P-SiO2@Au NPs) via one-step aqueous synthesis from chloroauric acid and tetraethyl orthosilicate mediated by a basic amino acid, arginine. Effects of chloroauric acid, tetraethyl orthosilicate, and arginine on the morphology and optical property of the products are investigated in detail. The P-SiO2@Au NPs achieve tunable plasmon resonance depending on the amount of chloroauric acid, which affects the size and shape of the P-SiO2@Au NPs. Finite-difference time-domain simulations are performed, revealing that the plasmon peak red-shifts with increasing particle size. Arginine serves as the reducing and capping agents for Au as well as the catalyst for SiO2 formation and also promotes the combination of Au and SiO2. Formation process of the P-SiO2@Au NPs is clarified through time-course analysis. The P-SiO2@Au NPs show good sensitivity for both colloidal and paper-based surface-enhanced Raman scattering measurements. They achieve enhancement factors of 4.3 × 107-8.5 × 107 and a mass detection limit of ca. 1 ng using thiophenol as the model analyte.

The Role Played by Graphene Oxide in the Photodeposition and Surface‐Enhanced Raman Scattering Activity of Plasmonic Ag Nanoparticle Substrates

Layer‐by‐layer photocatalyst films made of TiO2 nanoparticles (TiO2NP) assembled with both poly(sodium 4‐styrenesulfonate) (PSS) and graphene oxide (GO) are used for the photodeposition of plasmonic Ag nanoparticles (AgNPs) and subsequently used in surface‐enhanced Raman scattering (SERS). Both photocatalyst films, TiO2NP/PSS and TiO2NP/GO, are capable of driving the formation of AgNP when they are wetted with a drop of AgNO3 diluted solution and submitted to UV irradiation (254 nm). The photodeposition of AgNP, as monitored by UV–vis spectroscopy, follows a first‐order kinetics process in both films and is slightly faster in the TiO2NP/PSS. In addition, scanning electron microscopy reveals that in the TiO2NP/PSS film, the photodeposited AgNPs are larger and isolated, whereas in the TiO2NP/GO film, they are smaller and highly interconnected. The SERS activity of the substrates is evaluated with rhodamine B. When samples are excited in resonance with rhodamine B absorption (514 nm), GO‐based substrates provide the largest enhancement because GO is able to quench the rhodamine B fluorescence, something that PSS is unable to do. Out of this condition (633 nm), the plasmonic effect of AgNP alone prevails regardless of the presence of GO.

Investigation of the Factors Influencing the Surface-Enhanced Raman Scattering Activity of Silver Nanoparticles

Surface-enhanced Raman scattering (SERS) is one of the most effective methods for applications in optical sensors and chemical analysis. However, control of the optimal conditions of substrates and the selection of chemical probes are two major challenges which have yet to be solved. In this work, using a simple seeded growth method, nanoparticles with different sizes and shapes were produced. The SERS enhancement factor for each nanoparticle size and shape obtained was evaluated based on three different analytes, methylene blue, Nile blue A and Rhodamine B. We found a maximum enhancement factor on the order of 106 for the case of silver nanorods and Rhodamine B. Considering the SERS performance for silver nanospheres, we observed a systematic increase in the sequence methylene blue-Nile blue A-Rhodamine B. The reason behind the enhanced efficiency is that the maximum of the surface plasmon resonance band of Rhodamine B is the closest to the Raman excitation wavelength. The study also demonstrates that a decrease in size of spherical nanoparticles can lead to an increased enhancement, resulting from a larger surface area for a smaller particle size. Compared with silver nanospheres, silver nanorods yielded a better SERS enhancement factor, as a result of shape anisotropy which significantly enhance the local field hotspots. For low concentration, the intensity of Raman bands increases linearly with increasing dye concentration, which could be useful for applications involving chemical sensors.

Fabrication and Surface-Enhanced Raman Scattering Activities of Cross-Linked Polyvinyl Alcohol/Ag Nanofibers

This work describes the fabrication steps and surface-enhanced Raman scattering (SERS) activities of the cross-linked polyvinyl alcohol (PVA)/Ag nanofibers. The water-insoluble electrospun PVA/Ag nanofibers were achieved by post-electrospinning treatment processes. Physical crosslinking was induced by heat treatments, while chemical crosslinking took place through the reactions with glutaraldehyde (GA). Scanning electron microscopy (SEM) images have shown that cross-linked PVA/Ag nanofibers remained mostly intact after immerging in water for 30 min. The testing of SERS activities was performed on these substrates using the methylene blue (MB) molecules as tested substances. The results have shown that the PVA/Ag nanofibers can be used as SERS substrates for rapid screening of biochemical substances. The Raman enhancement factor (EF) of approximately 104 corresponding to the detection limit of 10-4 M of MB molecules was achieved.

Facile One-Pot Synthesis of Nanodot-Decorated Gold-Silver Alloy Nanoboxes for Single-Particle Surface-Enhanced Raman Scattering Activity.

Surface-enhanced Raman scattering (SERS) is an important, highly sensitive technique for chemical and biological analysis, which is critically dependent upon high-performance metallic substrates. Anisotropic gold (Au)-silver (Ag) alloy nanoboxes are attractive SERS substrates because of the greatly enhanced Raman signals from the strong electromagnetic fields on the sharp corners. Yet, the routine approach of Au-Ag alloy nanobox synthesis is still challenging because of the complicated procedures and use of biologically/environmentally unfriendly reagents. To facilitate the usage of Au-Ag alloy nanoboxes for broad SERS applications, we propose a facile green strategy to synthesize Au-Ag alloy nanoboxes with superior single-particle SERS sensitivity. Our novel straightforward strategy involves HAuCl4 and AgNO3 reduction by ascorbic acid, which is achieved in an aqueous one-pot reaction at ambient temperature. Significantly, the surfaces of the prepared Au-Ag alloy nanoboxes are judiciously designed to introduce nanodots, generating numerous "hot spots" for high Raman signal enhancement as indicated by rigorous numerical simulations. By combining scanning electron microscopy and Raman mapping images, we demonstrate the application of Au-Ag alloy nanoboxes for single-particle sensing SERS activity. The as-prepared Au-Ag alloy nanoboxes are expected to facilitate their further applications in quantitative and ultrasensitive SERS detection.

Synthesis of Silver Nanostructures and their Application in Highly Sensitive SERS Sensors

<p class="p1">A comparison of Surface Enhanced Raman Scattering (SERS) activity of chemically synthesised silver nanostructures with different shapes is reported. The silver nanostructures of cubical, prism and wire like morphology were synthesised using chemical synthesis route and utilised as SERS substrates. The sensors were fabricated by spin coating these materials over a Silicon or glass substrate. The fabricated sensors were used to analyse response with two different analytes, 4-Mercaptobenzoic acid and Rhodamine 6G under different concentrations. The signal enhancement was compared with a silver coated thin film over glass substrate and it was observed that the enhancement of the order of 10<span class="s1"><sup>3 </sup></span>is achieved. The nanowire performed better than the other forms of silver and gave a higher signal enhancement for all the analytes as compared to other nanostructures. The fabricated sensors may be useful for various applications including explosive and biowarfare agent detection.</p>

Preparation of Silver Nanocap Arrays and Their Surface‐enhanced Raman Scattering Activity

In this article, a surface‐enhanced Raman scattering (SERS) substrate of silver nanocap arrays was reported. With increasing the size of nanocaps, the localized surface plasmon resonance (LSPR) of the arrays exhibited tunable ability in the visible spectral region. The optical response of the nanocap arrays stimulated their use in SERS experiments. The assessment of SERS activity of the nanocap arrays was performed by using the 514.5 nm excitation line, and different average enhancement factor (EF) values were obtained. The good tunability of LSPR, relatively high average EF values and long‐range order of these substrates suggest that the silver nanocap arrays have promising applications as functional components in spectroscopy, immunoassay, biosensors, and biochips.

“Green” seed-mediated synthesis and morphology of Au nanoparticles using β-cyclodextrin

Gold nanoparticles (NPs) with dendritic morphology were synthesized by a “green” seed-mediated approach in the presence of β-cyclodextrin (β-CD) as stabilizing biocompatible capping agent. First, 50 mL of an aqueous solution containing 5 mM of β-CD were prepared, to which a variable amount of HAuCl4 was added. The β-CD/Au molar ratio was monitored from 20 to 200. Optical properties, including Surface-Enhanced Raman Scattering (SERS) activity, of the synthesized structures were characterized by Raman and UV-vis spectroscopies. Morphology was studied by transmission electron microscopy (TEM). Samples prepared using this procedure presents an increase of their SERS signal with respect to samples without peak-rich morphology. Optimized nanodendrites were obtained at a β-CD/Au molar ratio of 100. Moreover, a growth mechanism is proposed to describe the β-cyclodextrin role in the synthesis of Au nanodendrites. The “green” seed-mediated synthesis technique used herein produces Au NPs with good biocompatibility pointing them out for biomedical applications.

Templated Growth of Surface Enhanced Raman Scattering-Active Branched Gold Nanoparticles within Radial Mesoporous Silica Shells.

Noble metal nanoparticles are widely used as probes or substrates for surface enhanced Raman scattering (SERS), due to their characteristic plasmon resonances in the visible and near-IR spectral ranges. Aiming at obtaining a versatile system with high SERS performance, we developed the synthesis of quasi-monodisperse, nonaggregated gold nanoparticles protected by radial mesoporous silica shells. The radial mesoporous channels were used as templates for the growth of gold tips branching out from the cores, thereby improving the plasmonic performance of the particles while favoring the localization of analyte molecules at high electric field regions: close to the tips, inside the pores. The method, which additionally provides control over tip length, was successfully applied to gold nanoparticles with various shapes, leading to materials with highly efficient SERS performance. The obtained nanoparticles are stable in ethanol and water upon thermal consolidation and can be safely stored as a powder.