Silver nanoparticles, nanoneedles and nanorings: impact of electromagnetic near-field on surface-enhanced Raman scattering.

The dimension of plasmonic nanostructures does matter in localizing electromagnetic (EM) field and improving surface-enhanced Raman scattering (SERS) activity. Zero-dimensional (0D), one-dimensional (1D) and two-dimensional (2D) plasmonic nanostructures are promising candidates to validate SERS enhancement and the mechanisms thereof. In this work, silver (Ag) nanoparticles (NPs), nanoneedles (NNs) and nanorings (NRs) have been considered to demonstrate the impact of EM near-field distributions on SERS of the corresponding 0D (i.e. Ag-NPs), 1D (i.e. Ag-NNs) and 2D (i.e. Ag-NRs) nanostructures. Ag-NPs, Ag-NNs and Ag-NRs fabricated on zinc oxide (ZnO) ultrathin layer through sputtering technique have been characterized thoroughly by high-resolution field emission scanning electron microscopy (FESEM). FESEM micrographs confirmed a relatively narrow size distribution, 48.88 ± 8.32 nm, of Ag-NPs along with an estimated coverage density of ∼4 × 1010 cm-2. In the case of 1D nanostructures, Ag-NNs were estimated to have a relatively broadened length distribution, 534.36 ± 85.61 nm, and relatively narrow base distribution, 77.39 ± 25.25 nm, along with an estimated coverage density of ∼5 × 108 cm-2. However, as for 2D nanostructures, the FESEM micrographs revealed that Ag-NRs consisted of Ag clusters of various shapes and sizes, instead of a perfect ring structure along with much lower coverage density, ∼8.05 × 103 cm-2. The same specimens were used in microscopic SERS measurements and SERS activities were evaluated for individual nanostructures using Rhodamine 6G as Raman-active dye. The SERS activity of Ag-NRs was found to be the highest with reference to those of Ag-NPs and Ag-NNs. The scenario was supported as well by EM near-field distributions extracted from finite difference time domain (FDTD) analysis. Three models were developed according to the FESEM micrographs of Ag-NPs, Ag-NNs and Ag-NRs nanostructures and FDTD analysis was carried out to understand EM near-field distributions for individual nanostructures. EM near-field distributions at different planes for individual models were extracted for s-, p- and 45° incident polarizations. Such a correlated investigation facilitated an understanding and correlation of the impact of EM near-field distributions on SERS of the corresponding 0D (i.e. Ag-NPs), 1D (i.e. Ag-NNs) and 2D (i.e. Ag-NRs) nanostructures.

Silver-Decorated Silicon Nanostructures: Fabrication and Characterization of Nanoscale Terraces as an Efficient SERS-Active Substrate.

Rich and highly dense surface-enhanced Raman (SERS) hotspots available in the SERS-active platform are highly anticipated in SERS measurements. In this work, conventional silicon wafer was treated to have wide exposure to terraces available within the silicon nanostructures (Si-NSs). High-resolution field emission scanning electron microscopic (FESEM) investigations confirmed that the terraces were several microns wide and spread over different steps. These terraces were further decorated with silver nanoparticles (Ag-NPs) of different shapes and sizes to achieve SERS-active hotspots. Based on more than 150 events, a histogram of the size distribution of Ag-NPs indicated a relatively narrow size distribution, 29.64 ± 4.66 nm. The coverage density was estimated to be ~4 × 1010 cm-2. The SERS-activity of Ag-NPs -decorated Si-NSs was found to be enhanced with reference to those obtained in pristine Si-NSs. Finite difference time domain models were developed to support experimental observations in view of electromagnetic (EM) near-field distributions. Three archetype models; (i) dimer of same constituent Ag-NPs, (ii) dimer of different constituent Ag-NPs, and (iii) linear trimer of different constituent Ag-NPs were developed. EM near-field distributions were extracted at different incident polarizations. Si-NSs are well-known to facilitate light confinement, and such confinement can be cascaded within different Ag-NPs-decorated terraces of Si-NSs.

Half-raspberry-like bimetallic nanoassembly: Interstitial dependent correlated surface plasmon resonances and surface-enhanced Raman spectroscopy.

Correlated localized surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS) and localized electromagnetic (EM) field distributions of pure and modified gold (Au) nanoassemblies have been demonstrated. The Au nanoassemblies were decorated as half-raspberry-like nanostructures by silver (Ag) mists, and the characteristics of their SPR and SERS were observed at the same spatial position with and without decoration. The decoration of Au nanoassemblies was analyzed in-depth and confirmed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). Multifunctional and lab-built microscopy was used to capture correlated SPR and SERS imaging and spectral measurements. Without decoration, strong SPR peaks and enhanced SERS signals were observed, whereas intense plasmon excitation deteriorated with a broadening and diminishing peak and the SERS enhancement dropped at least by 10 fold upon the modification. Preferential enhancement near the edge was observed in the correlated SPR and SERS measurements. The variations in localized SPR, subsequent SERS enhancement, and preferential confinement were speculated concerning localized EM near-field deformation. A typical tetramer with five interstitials was modeled and simulated by finite difference time domain (FDTD) analysis at different incident polarizations. The EM near-field distributions were extracted with and without decoration of constituent interstitials by Ag mists. Without the modification of participating interstitials, the EM near-field distributions were found confined, whereas additional EM near-field confinements were observed in the presence of Ag mists. Such EM near-field deformations due to the modification of constituent interstitials were supposed to broaden and deteriorate SPR characteristics of Au nanoassemblies as observed under this investigation.

Frailty indexed classification of Bangladeshi older adults' physio-psychosocial health and associated risk factors- a cross-sectional survey study.

BACKGROUND: Frailty is associated with healthy ageing, and it has been identified as a means of measuring older adults' physio-psychosocial health. We know about the ageing trends and common diseases of older adults living in South Asia, but literature to date does not widely feature their health status based on frailty, especially in Bangladesh. This study aims to understand the prevalence of frailty in Bangladeshi older adults; classify their health status; and investigate associated risk factors. METHODS: A cross-sectional study was conducted in the north-eastern region (i.e. Sylhet City Corporation) of Bangladesh. Four hundred participants aged 55 years and above were randomly selected, attended a health assessment session and completed a multi-indicator survey questionnaire. We developed a 30-indicator Frailty Index (FI30) to assess the participant's health status and categorized: good health (no-frailty/Fit); slightly poor health (mild frailty); poor health (moderate frailty); and very poor health (severe frailty). Pearson chi-square test and binary logistic regression analysis were conducted. RESULTS: The participants' mean age was 63.6 years, and 61.6% of them were assessed in poor to very poor health (moderate frailty/36.3% - severe frailty/25.3%). The eldest, female and participants from lower family income were found more frailty than their counterparts. Participants aged 70 years and above were more likely (adjusted OR: 4.23, 95% CI: 2.26-7.92, p < 0.0001) to experience frailty (medical conditions) than the pre-elderly age group (55-59 years). Female participants were more vulnerable (adjusted OR = 1.487, 95% CI: 0.84-2.64, p < 0.0174) to frailty (medical conditions) than male. Also, older adults who had higher family income (Income>$473.3) found a lower risk (adjusted OR: 0.294, 95% CI: 0.11-0.76, p < 0.011) of frailty (poor health). CONCLUSION: Our study results confirm the prevalence of frailty-related disorders in Bangladeshi older adults and highlight the importance of targeted clinical and community-led preventive care programs.

Anisotropic gold nanoassembly: a study on polarization-dependent and polarization-selective surface-enhanced Raman scattering.

A simple one-step process was adopted to fabricate anisotropic gold nanoassemblies. Evaporation-assisted nanoparticle assembly at the meniscus was maintained in this regard. Scanning electron microscopy confirmed that the constituent nanoparticles of the anisotropic gold nanoassembly are neither in physical contact nor agglomerated; instead, they are separated by a small interparticle gap. Crystal violet was adsorbed on the anisotropic gold nanoassembly, and a large enhancement (several orders of magnitude) in surface-enhanced Raman scattering (SERS) was observed. The assembly was thus proved to be highly SERS-active. Such an anisotropic gold nanoassembly allowed polarization dependent and polarization selective SERS experiments to be carried out. Inhomogeneous SERS and surface plasmon resonance distribution were observed along the assembly. Polarization-dependent SERS enhancement reached its highest value at in-plane polarization to the long axis, whereas polarization-selective SERS characteristics at the same spatial position showed uniform enhancement. Fluorescence emission accompanied with SERS signals was also characterized. Polarization-dependent fluorescence was enhanced at in-plane polarization to the long axis, whereas polarization-selective fluorescence was not enhanced. The experimental results were correlated and explained with three-dimensional finite definite time domain simulations as well. Such interstitial-limited gold nanoassembly provides means to realize polarized SERS characteristics for ensemble SERS measurements, which are important not only for the application-oriented fabrication of SERS-active substrates but also for understanding their feasibility in those applications.

Detection of surface enhanced Raman scattering active hotspot using near field scanning optical microscopy.

Hotspots are high-intensity electromagnetic zones that form, for example, at the interstitials of plasmonic nanoaggregates, resulting in a considerable rise in the enhancement factor. However, it is inevitable to achieve specific nanometric geometry as well as a suitable technique to capture the details of hotspots. We report near-field surface-enhanced Raman scattering (SERS) spectroscopy of a well-defined gold nanoaggregate of a few nanoparticles adsorbed with a small number of target analytes. A spectrally and spatially resolved SERS measurement setup using an aperture near-field scanning optical microscope (a-NSOM) facilitated the direct observation of localized electromagnetic (EM) fields at the interstitials through SERS. Correlated optical image and corresponding nanometric geometry were captured through the home-built a-NSOM setup. Near-field SERS spectra were recorded at different sites of interest. It was evident that the interstitial positioned at the center of the tetramer provided the most intense Raman scattering, implying the possibility of a SERS-active hotspot therein. SERS bands of the spectrum of the Raman-active dye Rhodamine 6G recorded at the same hotspot coincided well with those reported so far. It was noteworthy that most of the SERS bands in such scenery got enhanced. Such direct observation with high spatial resolution is indispensable to understanding the origin of localized EM fields at "hotspots" and the EM enhancement factor in the SERS process. A finite-difference time-domain (FDTD) analysis was carried out to validate the results.

Behavioral intentions of university teachers and students toward the adoption of the hyb-blended learning method: Evidence from Bangladesh.

Hyb-blended learning is a novel method that can serve as a substitute for conventional classroom-based learning activities, demonstrating effectiveness in both pandemics like COVID-19 and other crises, as well as in non-pandemic situations. The successful application of this method in the field of education depends on the users' intentions to adopt it. Therefore, this study aims to understand the behavioral intentions of teachers and students at Bangladeshi universities toward the adoption of the hyb-blended learning method. A correlational, cross-sectional, and sample survey-based research design was employed. Two structured questionnaires, one for teachers and one for students, were used to collect data from 171 teachers and 713 students from 11 public and 8 private universities in Bangladesh. The conceptual model of the study was developed on the theoretical underpinnings of the "Unified Theory of Acceptance and Use of Technology (UTAUT)." The study used a structural equation modeling technique to test the hypotheses. The results of the study revealed that the proposed learning method would increase teaching and learning opportunities for both teachers and students in Bangladeshi universities. They would adopt this method without relying on the experiences of others or what others think or say. Unlike teachers, the study also found that students would use it if they received support and influence from friends, fellow students, university authorities, and other external factors. However, their intentions toward adopting this method depend on the availability of resources and support for adopting it, as well as adequate and necessary understanding and talent to use it effectively. Results also revealed that they would adopt the method if it was found to be simple to use. The study has a notable practical implication, as it has proposed an alternative learning and teaching method that would be effective in Bangladeshi universities during the COVID-19 pandemic or other crises and in non-pandemic situations as well.

Efficient rhodamine B dye photocatalytic degradation in aqueous media using novel ZnO nanomaterials co-doped with Ce and Dy.

Water pollution caused by dyes and industrial wastewater poses a significant threat to ecosystems. The purification of such pollutants presents a major challenge. Photocatalysis based on semiconductor materials is a potential wastewater treatment process due to its safety and cost-effectiveness. In the present work, Zn1-2xCexDyxO (x = 0.01-0.05) semiconductors were prepared by the sol-gel auto-ignition method. The samples are denoted CDZO1, CDZO3, and CDZO5 for x  = 0.01-0.05, respectively. The X-ray diffraction and Raman spectroscopy results revealed the formation of ZnO hexagonal phase wurtzite structure for all synthesized compositions. Different structural properties were determined. It was found that the lattice parameters and the unit cell volume increased, while the crystallite size diminished as x varied from 0.01 to 0.05. Transmission electron microscopy observations confirmed the formation of nanoparticles with the desired chemical compositions. The specific surface area (SSA) values are found to be 39.95 m2/g, 48.62 m2/g, and 51.36 m2/g for CDZO1, CDZO5, and CDZO5 samples, respectively. The reflectance spectra were recorded to examine the optical properties of the different nanoparticles. The values of the optical band gap were 3.221, 3.225, and 3.239 eV for CDZO1, CDZO3, and CDZO5 samples, respectively. In addition, the photocatalytic performance towards RhB dye degradation for the different samples was assessed. It was established that the CDZO3 sample with a moderate SSA value exhibited the superior photocatalytic performance among the other as-prepared samples wherein the percentage of degradation efficiency, and kinetic constant rate attained their maximum values of 98.22 % and 0.0521 min-1, respectively within 75 min. As per the obtained findings, it is evident that the Zn1-2xCexDyxO photocatalyst has prominent potential for use in the degradation of dyes and offers a useful route for impeding the recombination of electron-hole pairs of zinc oxide material.

Understanding the impact of socioeconomic and health factors on geriatric depression: A comparative study in rural and urban Bangladesh.

Background and Aims: The prevalence of depression among the elderly is a growing concern, and this study examines the differences between urban and rural areas in terms of geriatric depression. Methods: Using a two-stage random sampling approach in urban areas and a multistage random sampling approach in rural areas, the study surveyed 944 elderly individuals of both sexes. Results: The results indicate that the prevalence of depression was high, with 52.5% of the elderly population experiencing mild to severe depression. The study found that increasing age, female gender, nuclear family structure, and involvement of housewives or others were significant factors affecting depression in urban areas, while increasing age and elderly people without spouses were significant factors in rural areas. Additionally, the study identified hearing impairment, asthma, and arthritis as risk factors for depression in rural areas, and bronchitis, heart disease, and thyroid illness as significant factors in urban areas. Conclusion: These findings highlight the need for policymakers to focus on addressing the mental health needs of older people, particularly women and those without spouses.

Financial progress, inward remittances, and economic growth in Bangladesh: Is the nexus asymmetric?

Prior studies in Bangladesh examined the effects of financial progress and inward remittances on economic growth and postulated a symmetrical relationship, ignoring the potential asymmetrical relationship between variables. Therefore, this study intends to explore the asymmetrical effects of financial progress and remittances on economic growth in Bangladesh. The study used yearly time series data from 1988 to 2020 and employed the Nonlinear Autoregressive Distributed Lag (NARDL) model. Our study confirmed the asymmetrical effects of financial progress and remittances on economic growth and revealed a long-run association between the variables being studied. The study's novelties are that both positive and negative fluctuations in financial progress and remittances boost Bangladesh's economic growth. Thus, it is essential to enact policies that support financial progress by ensuring sustainable development in financial institutions and financial markets. In addition, remittances should be employed for productive purposes rather than only for consumption to improve the country's economic backbone.

Chemiresistive Gas Sensing using Graphene-Metal Oxide Hybrids.

Chemiresistive sensing lies in its ability to provide fast, accurate, and reliable detection of various gases in a cost-effective and non-invasive manner. In this context, graphene-functionalized metal oxides play crucial role in hydrogen gas sensing. However, a cost-effective, defect-free, and large production schemes of graphene-based sensors are required for industrial applications. This review focuses on graphene-functionalized metal oxide nanostructures designed for gaseous molecules detection, mainly hydrogen gas sensing applications. For the convenience of the reader and to understand the role of graphene-metal oxide hybrids (GMOH) in gas sensing activities, a brief overview of the properties and synthesis routes of graphene and GMOH have been reported in this paper. Metal oxides play an essential role in the GMOH construct for hydrogen gas sensing. Therefore, various metal oxides-decorated GMOH constructs are detailed in this review as gas sensing platforms, particularly for hydrogen detection. Finally, specific directions for future research works and challenges ahead in designing highly selective and sensitive hydrogen gas sensors have been highlighted. As illustrated in this review, understanding of the metal oxides-decorated GMOH constructs is expected to guide ones in developing emerging hybrid nanomaterials that are suitable for hydrogen gas sensing applications.

Fabrication and Characterization of Au-Decorated MCM-41 Mesoporous Spheres Using Laser-Ablation Technique.

This study reports the synthesis of Au-decorated MCM-41 mesoporous nanoparticles using a laser-ablation technique. It was observed that the number of Au attached to MCM-41 nanostructures was dependent on the amount of encapsulated Cationic surfactant (cetyl ammonium bromide (CTAB) volume. The chemical group of the prepared nanoparticles was analyzed by FT-IR spectroscopy, where different absorption peaks corresponding to Au and MCM-41 were observed. The observed band region was ∼1090, 966, 801, 2918, and 1847 cm-1 for different samples, clearly confirming the successful preparation of MCM-41 with CTAB and Au-decorated MCM-41 nanoparticles using environmentally friendly laser-ablation approach. The surface morphology of the prepared nanoparticles were performed using TEM techniques. The TEM analysis of the MCM-41 specimen showed silica spheres with an average size of around 200 nm. Furthermore, Raman spectroscopy was done to evaluate the chemical structure of the prepared nanoparticles. It was seen that the prepared Au NPs decorated the MCM-41 system facilitated strong Raman peaks of CTAB. In addition, eight distinct Raman peaks were observed in the presence of Au NPs. This new functionalized method using the laser-ablation approach for mesoporous nanoparticles will participate effectively in multiple applications, especially the encapsulated molecule sensing and detection.

Clusters-based silver nanorings: An active substrate for surface-enhanced Raman scattering.

Plasmonic nanostructures, particularly irregular surfaces of ring-like silver (Ag) nanostructures are promising candidates in surface-enhanced Raman scattering (SERS) spectroscopy. In this work, clusters-based Ag nanorings have been fabricated and characterized as SERS-active substrates. The rim of the as-fabricated Ag nanorings was found neither discontinuous nor linear aggregation of nanoparticles. High-resolution field emission scanning electron microscopy (FESEM) revealed that the individual constituent clusters were different from each other, particularly in terms of size and shape in addition to the cases how such clusters were emerged as the edge of the nanoring. Considering the dimensions of the clusters and the arrangement of such clusters as nanorings, it was speculated that the local electromagnetic (EM) near-field distributions would excel and thus enhanced SERS signals would be achieved. Indeed, the inherent features of the nanorings facilitated to achieve SERS enhancement factors as high as 2.1 × 104. SERS-activity of as-fabricated Ag nanorings was confirmed using Rhodamine 6G (R6G) as Raman-active dyes and the enhancement was compared to those obtained from R6G adsorbed on Ag-ZnO/Glass and ZnO/Glass. To the best of our knowledge, this is the first attempt to explore the impact of localized EM near-field within the segments of nanorings through SERS spectroscopy. A model was designed resembling the nanorings under this investigation to simulate EM near-field distributions by finite difference time domain (FDTD) analysis. The dimensions of the model geometry were chosen according to the observations achieved by FESEM. To simplify the simulations, nanoobjects were considered spherical and organized in a periodic fashion, although the constituent clusters of Ag nanorings were found irregular in shape and arrangement. Since EM near-field distribution highly depends on interparticle gaps, three scenarios were implemented, such as, small gap in between two adjacent nanoobjects and adjacent nanoobjects in touch and overlapped. Each configuration was simulated and EM near-field distribution was extracted for s-, p- and 450 of incident polarizations followed by a plausible correlation to SERS enhancements. Such correlated investigations as well as clusters-based Ag nanorings not only inspire the ones to look for cost-effective SERS-active substrate, but also understand the underlying EM mechanism in SERS enhancements.

Polymer-Templated Durable and Hydrophobic Nanostructures for Hydrogen Gas Sensing Applications.

A simple and hands-on one-step process has been implemented to fabricate polymer-templated hydrophobic nanostructures as hydrogen gas sensing platforms. Topographic measurements have confirmed irregular hills and dips of various dimensions that are responsible for creating air bubble pockets that satisfy the Cassie-Baxter state of hydrophobicity. High-resolution field-emission scanning electron microscopy (FESEM) has revealed double-layer structures consisting of fine microscopic flower-like structures of nanoscale petals on the top of base nanostructures. Wetting contact angle (WCA) measurements further revealed the contact angle to be ~142.0° ± 10.0°. Such hydrophobic nanostructures were expected to provide a platform for gas-sensing materials of a higher surface area. From this direction, a very thin layer of palladium, ca. 100 nm of thickness, was sputtered. Thereafter, further topographic and WCA measurements were carried out. FESEM micrographs revealed that microscopic flower-like structures of nanoscale petals remained intact. A sessile drop test reconfirmed a WCA of as high as ~130.0° ± 10.0°. Due to the inherent features of hydrophobic nanostructures, a wider surface area was expected that can be useful for higher target gas adsorption sites. In this context, a customized sensing facility was set up, and H2 gas sensing performance was carried out. The surface nanostructures were found to be very stable and durable over the course of a year and beyond. A polymer-based hydrophobic gas-sensing platform as investigated in this study will play a dual role in hydrophobicity as well as superior gas-sensing characteristics.

Plasmonic Pollen Grain Nanostructures: A Three-Dimensional Surface-Enhanced Raman Scattering (SERS)-Active Substrate.

A new route has been developed to design plasmonic pollen grain-like nanostructures (PGNSs) as surface-enhanced Raman scattering (SERS)-active substrate. The nanostructures consisting of silver (Ag) and gold (Au) nanoparticles along with zinc oxide (ZnO) nanoclusters as spacers were found highly SERS-active. The morphology of PGNSs and those obtained in the intermediate stage along with each elemental evolution has been investigated by a high-resolution field emission scanning electron microscopy. The optical band gaps and crystal structure have been identified by UV-vis absorption and X-ray powder diffraction (XRD) measurements, respectively. For PGNSs specimen, three distinct absorption bands related to constituent elements Ag, Au, and ZnO were observed, whereas XRD peaks confirmed the existence of Ag, Au, and ZnO within the composition of PGNSs. SERS-activity of PGNSs was confirmed using Rhodamine 6G (R6G) as Raman-active dyes. Air-cooled solid-state laser kits of 532 nm were used as excitation sources in SERS measurements. SERS enhancement factor was estimated for PGNSs specimen and was found as high as 3.5×106 . Finite difference time domain analysis was carried out to correlate the electromagnetic (EM) near-field distributions with the experiment results achieved under this investigation. EM near-field distributions at different planes were extracted for s-, p- and 45° of incident polarizations. EM near-field distributions for such nanostructures as well as current density distributions under different circumstances were demonstrated and plausible scenarios were elucidated given SERS enhancements. Such generic fabrication route as well as correlated investigation is not only indispensable to realize the potential of SERS applications but also unveil the underneath plasmonic characteristics of complex SERS-active nanostructures.

Nanoassembly of gold nanoparticles: An active substrate for size-dependent surface-enhanced Raman scattering.

Nanoassembly of gold nanoparticles has been achieved through a simple and facile process without using any surfactants or linkers. Atomic force microscopy confirmed assemblies of several tens of microns, whereas tiny interparticle gaps less than 5 nm was revealed by scanning electron microscopy. Such nanoassemblies with tiny interparticle gaps were found to be highly surface-enhanced Raman scattering (SERS)-active with enhancement factor in the order of 6 to 8. Contrary to usual trends in nanoparticles size dependent SERS enhancement, such 2D nanoassemblies of different sizes of nanoparticles showed relatively broadened SERS enhancement distribution. Finite difference time domain (FDTD) analysis was employed to highlight the EM-field distribution in connection to such giant SERS enhancement. In depth and hotsite-wise analysis on EM near-field distributions for monomers, dimers and septamers of 50 nm of gold nanoparticles were carried out at three specific incident polarizations (i.e. s-, 45° and p-polarizations). At s- and p-polarization the strongest hotsites were having the EM near-field distributions in the range of 124.8 and 133.3 V/m respectively with lower population of confined EM near-fields. Such correlated investigation will be indispensable to understand and interpret hierarchical and functional nanoassemblies from its unit nanoparticle blocks for the advances of technological breakthroughs.

Development of a heat-induced surface-enhanced Raman scattering sensing method for rapid detection of glutathione in aqueous solutions.

In this paper, a direct and simple detection method based on surface-enhanced Raman scattering (SERS) named "heat-induced SERS sensing method" is proposed for rapid determination of glutathione in aqueous solutions. It was found that highly enhanced SERS spectra of glutathione can be obtained if the silver colloids adsorbed with the analyte were heated up before the SERS measurement. Besides, it was revealed that silver particles with a size of approximately 60 nm are suitable for this study and that the SERS intensity is also influenced by the dropped sample volume, drying temperature, buffer concentration, and pH of the solution. It is noted that the thiol group of glutathione has a particularly strong interaction with a silver surface compared with other small biological molecules without a thiol group, validating this method to detect glutathione selectively. Under the optimal conditions, the detection of glutathione can be finished within 5 min, and the detection limit of ca. 50 nM can be reached, which is much better than the reported detection limit of glutathione (approximately 1 microM) by SERS. The enhancement factor of the proposed heat-induced SERS sensing method for the detection of glutathione is about 7.5 x 10(6). The proposed method holds a specific selectivity toward glutathione, facilitating its rapid detection in practical applications.

A novel reversed reporting agent method for surface-enhanced Raman scattering; highly sensitive detection of glutathione in aqueous solutions.

In this study, a new application method for SERS named "reversed reporting agent" method is proposed for selective detection of biomolecules with a thiol group. In this method reporting agents such as rhodamine 6G (R6G) are capped on surfaces of silver colloidal nanoparticles. Analytes having a thiol group will replace the positions of reporting agents due to the strong interactions between silver and the thiol group, and then the SERS intensity of the reporting agents will be reduced. By monitoring the difference in the SERS intensity of reporting agents before and after the replacement of analytes, the concentration of the analytes can be estimated. To demonstrate the feasibility of this proposed method, glutathione was used as the analyte and R6G, crystal violet (CV), and thiacyanine (TC) were employed as the reporting agents, and factors that affect the capability of the determination of glutathione were investigated. The results indicate that R6G is the most suitable reporting agent, and the concentration of the reporting agents affects the sensitivity and selectivity of glutathione determination. Under the optimal conditions, the detection of glutathione can be finished within 20 minutes and the detection limit of ca. 1 microM can be achieved. Furthermore, the proposed method holds specific selectivity towards glutathione, which means it has possible practical applications.

Surface-enhanced Raman scattering: realization of localized surface plasmon resonance using unique substrates and methods.

Surface-enhanced Raman scattering (SERS) enhancement and the reproducibility of the SERS signal strongly reflect the quality and nature of the SERS substrates because of diverse localized surface plasmon resonance (LSPR) excitations excited at interstitials or sharp edges. LSPR excitations are the most important ingredients for achieving huge enhancements in the SERS process. In this report, we introduce several gold and silver nanoparticle-based SERS-active substrates developed solely by us and use these substrates to investigate the influence of LSPR excitations on SERS. SERS-active gold substrates were fabricated by immobilizing colloidal gold nanoparticles on glass slides without using any surfactants or electrolytes, whereas most of the SERS-active substrates that use colloidal gold/silver nanoparticles are not free of surfactant. Isolated aggregates, chain-like elongated aggregates and two-dimensional (2D) nanostructures were found to consist mostly of monolayers rather than agglomerations. With reference to correlated LSPR and SERS, combined experiments were carried out on a single platform at the same spatial position. The isolated aggregates mostly show a broadened and shifted SPR peak, whereas a weak blue-shifted peak is observed near 430 nm in addition to broadened peaks centered at 635 and 720 nm in the red spectral region in the chain-like elongated aggregates. In the case of 2D nanostructures, several SPR peaks are observed in diverse frequency regions. The characteristics of LSPR and SERS for the same gold nanoaggregates lead to a good correlation between SPR and SERS images. The elongated gold nanostructures show a higher enhancement of the Raman signal than the the isolated and 2D samples. In the case of SERS-active silver substrates for protein detection, a new approach has been adopted, in contrast to the conventional fabrication method. Colloidal silver nanoparticles are immobilized on the protein functionalized glass slides, and further SERS measurements are carried out based on LSPR excitations. A new strategy for the detection of biomolecules, particularly glutathione, under aqueous conditions is proposed. Finally, supramolecular J-aggregates of ionic dyes incorporated with silver colloidal aggregates are characterized by SERS measurements and correlated to finite-difference time-domain analysis with reference to LSPR excitations.

A study of glutathione molecules adsorbed on silver surfaces under different chemical environments by surface-enhanced Raman scattering in combination with the heat-induced sensing method.

In this study, surface-enhanced Raman scattering (SERS) in combination with a heat-induced sensing technique has been applied for investigating molecular orientations of glutathione molecules adsorbed on silver colloidal nanoparticles under different chemical environments, which has enabled us to further study how glutathione molecules are adsorbed on the silver surfaces. Factors that may affect the configurations of glutathione molecules adsorbed on the silver nanocolloids have been investigated. By observing the relative enhancement factors of SERS bands due to individual functional groups contributed from different terminals, the affinity between the different functional groups of glutathione and the silver surfaces under different conditions has been sorted and the orientations of glutathione molecules adsorbed on the silver surfaces have been investigated.