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Surface-enhanced Raman scattering (SERS) has outstanding merits in biochemical molecular analysis, and the development of new SERS substrates is the focus of research. Herein, In 2 O 3 nanoparticles (NPs) were synthesized by a high temperature pyrolysis method with cubic phase and small particle size at 10 nm. The structures and properties of In 2 O 3 NPs were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM) and other characterization methods. Additionally, the SERS spectra of In 2 O 3 -MBA with the enhancement factor (EF) up to 1.22 × 10 4 is discussed. The results demonstrate that there is a charge transfer (CT) effect revealed between the adsorbed molecules of 4-mercaptobenzoic acid (4-MBA) and the substrates of In 2 O 3 NPs, and it could be excited by long wavelength energy. Based on the In 2 O 3 NPs, the study is beneficial to develop more potential semiconductor SERS substrates., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The application of surface enhanced infrared absorption (SEIRA) is severely restricted in many fields due to the SEIRA substrates are constructed mainly from expensive noble metals. Therefore, the development of new SEIRA substrates other than the noble metallic ones is very valuable. Here we introduced a new semiconductor SEIRA substrate, the indium tin oxide (ITO) nanoparticles (NPs), to study the SEIRA property. The results demonstrate that the ITO NPs show the SEIRA property and the enhancement is dependent to the doping ratio of the heteroatoms of tin. The ITO NPs with the 5% atomic doping ratio show the highest SEIRA enhancement factor (EF), which is about 24. The limit of detection (LOD) of the 1,1'-dicarboxyferrocene (dcFc) molecule was as low as 10 -5  mol/L. The present study proves that the tin-doped indium oxide can be used as a new and inexpensive semiconductor SEIRA substrate. It also proves that the doped semiconductor NPs have strong potentials for being used as emerging SEIRA substrates., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Surface-enhanced Raman scattering (SERS) has been applied in many fields, but still has the limitation of widespread applications on semiconductor substrates. In this work, a series of antimony-doped tin oxide (ATO) nanoparticles (NPs) have been synthesized by a hydrothermal method and were used as SERS substrates for the first time. Interestingly, a charge transfer (CT) effect was revealed between the probing molecules of 4-mercaptobenzoic acid (4-MBA) and the substrates of ATO NPs, which accounts for the SERS enhancement and shows dependence to the Sb ions doping ratios in ATO NPs. By considering the energy level diagram of the ATO-MBA complexes and the doping theory of semiconductors, this phenomenon is believed to connect to the variance of the optical band gap energy (E g ), which is accompanied with the changes of free charge carrier densities in conduction bands (CBs) of ATO NPs due to different doping contents. The study of the E g - or free-charge-carrier-density-dependent property of the semiconductor-based SERS provides a new point of view for the development of new semiconductor SERS substrates and also contributes to the SERS CT mechanism., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

p-Aminothiophenol (PATP) is a preferred molecule in research on surface-enhanced Raman scattering (SERS) because of its unique characteristics of high spectral activity, easily induced charge-transfer (CT), and sensitivity to molecular structural changes. However, some aspects are still unclear, such as the initial steady state of PATP on noble metallic substrates without strong additional excitation with incident and/or induced electromagnetic radiation. Information about the initial steady state, especially the intrinsic CT state, is of great importance to elucidate the dynamic processes of CT and/or molecular structural changes under additional excitation. To investigate the native state of an adsorbed molecule, a suitable probe method that does not disrupt the native state of the whole system, including both molecules and substrates, is required. SERS is not applied in this context because of its use of high-energy visible and near-infrared light. Herein, a low-energy probe method, surface-enhanced infrared-absorption (SEIRA) spectroscopy, is employed as a suitable method for studying the native adsorption state of PATP on silver nanoisland films. The molecular structure and adsorption state were investigated. The intrinsic CT state received particular attention by analyzing the CT-related vibration of B 2 modes. Using Fourier transform infrared (FTIR), transmission SEIRA and reflection SEIRA spectroscopy, we explained why the relative intensities of some bands were different under different conditions. A quasi-standing orientation of PATP adsorbed on the substrates was also confirmed. More importantly, we demonstrated that there is no perceptible CT between PATP and silver nanoisland films; in contrast, CT generally occurs in a disruptive manner in SERS. Density functional theory (DFT) calculations and the selection rules for infrared (IR) transmission and reflection-absorption spectroscopy were used to analyze the spectra throughout the paper. SEIRA proved to be an effective technique to explore the native adsorption state of molecules without the excessive external disturbance induced by excitation. The results are very important in providing insight into molecules in surface-interface chemistry, enhanced spectroscopy and photoelectronics., (Copyright © 2018 Elsevier B.V. All rights reserved.)

With the explosive application of methyl salicylate (MS) molecules in food and cosmetics, the further detection of MS molecules becomes particularly important. Here we investigated the detection of MS molecules based on surface-enhanced Raman scattering (SERS) in a novel molecule/assistant/metal system constructed with MS, 4,4'-(hexafluoroisopropylidene) bis (benzoic acid) and Ag nanoparticles (AgNPs). The minimum detection concentration is 10 -4  M. To explore the function of assisted reagent, we also referred another system without assistant molecules. The result demonstrates that SERS signals were not acquired, which proves that the assistant molecules are critical for the capture of MS molecules. Two possible mechanisms of MS/assistant/AgNPs system were speculated through two patterns of hydrogen bonds. The linker molecules acted as the role of the bridge between metallic substrates and target molecules through the molecular recognition. This strategy is very beneficial to the expanding of MS detection techniques and other hydrogen bond based coupling detections with SERS., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) simulations were employed to study 5-amino-2-mercaptobenzimidazole (5-A-2MBI) molecules. Ag colloids were used as SERS substrates which were prepared by using hydroxylamine hydrochloride as reducing agent. Raman vibration modes and SERS characteristic peaks of 5-A-2MBI were assigned with the aid of DFT calculations. The molecular electrostatic potential (MEP) of 5-A-2MBI was used to discuss the possible adsorption behavior of 5-A-2MBI on Ag colloids. The spectral analysis showed that 5-A-2MBI molecules were slightly titled via the sulfur atoms adhering to the surfaces of Ag substrates. The obtained SERS spectral intensity decreased when lowering the 5-A-2MBI concentrations. A final detection limit on the concentration of 5×10(-7) mol · L(-1) was gained. SERS proved to be a simple, fast and reliable method for the detection and characterization of 5-A-2MBI molecules., (Copyright © 2015 Elsevier B.V. All rights reserved.)

At present, fluorescence spectroscopy, ultraviolet spectroscopy and infrared spectroscopy are usually used to detect drug molecules, however the information about using Raman spectroscopy to detect drug molecules is very few. In this work normal Raman spectroscopy and surface-enhanced Raman spectroscopy were utilized to study benzylpenicillin sodium (NaBP). The results show that NaBP is close to the surface of silver substrate through the carboxyl group, and the detection limit of NaBP is reduced to 1×10(-7) mol/L. Accordingly, the quantitative analysis of NaBP can be carried out in the range of 1×10(-4)-1×10(-7) mol/L concentration. And it is proved that NaBP is not stable in acid and alkali conditions and the decomposition reaction is very complex., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Long range ordered silver nanotriangles array was fabricated for surface-enhanced fluorescent immunoassay in this paper. By polystyrene (PS) microspheres based LB template method, the silver nanotriangle array with about 100 nm in height was constructed on the surface of glass slide. On the surface of Ag nanotriangles array, the immune reaction of antigens and labeled antibodies was carried out. Based on the interaction of fluorophores from antibodies with the plasmon resonance from Ag nanotriangles and the enrichment effect of this patterned array, 3.11 times enhancement of the fluorescent intensity of the target antibodies was obtained. According to the fitting curve of fluorescent intensities and logarithmic concentrations of labeled antibodies from 100 pg/mL to 10 μg/mL, it concludes that the limit of detection by this Ag nanotriangles array for immune complex is 100 pg/mL. Due to the advantages of high sensitivity, good reproducibility, and convenient fabrication, the 2D silver nanotriangles array could be an exciting platform for bioassays in proteomics, drug discovery and diagnostics., (Copyright © 2014 Elsevier B.V. All rights reserved.)

By the aim of constructing surfaces for multi-component and multifunctional bioassay, a microsphere lithography technique was employed to control the surface morphology. Two kinds of protein molecules (antibodies) were used as building blocks. As a result, dual-component biocompatible surfaces with alternate immunoglobulin micropatterns were fabricated. The employed antibodies included human Immunoglobulin G (IgG) and rabbit IgG, which composed nanometer scale surface arrays on the surfaces. The antibodies were identified specially by immunoreactions with labeled antigens of fluorescein isothiocyanate (FITC)-antihuman IgG and tetramethylrhodamine-5-(and 6)-isothiocyanate (TRITC)-antirabbit IgG. The immune responses were confirmed by confocal fluorescence (FL) microscopy. A study on the sensitivity and quantification was done by using surface-enhanced resonance Raman scattering (SERRS) spectroscopy. The obtained SERRS spectra showed satisfactory resolution in the multi-component detection objects. No interference was observed from inner- or interactions of detecting molecules. The detection limits for both of the antigens reached to as low as 1 ng/mL, which was comparable to FL method. Meanwhile, a good linear relationship between SERRS peak intensity and the logarithm of antigens' concentrations (from 1 ng/mL to 1 mg/mL) were observed. The results demonstrated that SERRS is a very promising detection technique for multi-component immunoassay, and has great potential applications in biotechnology and biochemistry., (Copyright © 2012 Elsevier B.V. All rights reserved.)

TiO(2) and Mn-doped TiO(2) (1%, 3% and 5%) nanoparticles (NPs) were synthesized by a sol-hydrothermal method for surface-enhanced Raman spectroscopy study. When using the 4-mercaptobenzoic acid (4-MBA) as the probing molecule, optimum SERS signals were observed on the Mn-TiO(2) (3%) samples. On the 3% Mn doped TiO(2) substrate, 4-MBA molecules exhibit a higher SERS intensity by a factor of six as compared with the native enhancement of 4-MBA adsorbed on pure TiO(2) NPs. The possible mechanism for the phenomena is also discussed. This study opens up a new dimension for the family of SERS substrates., (Copyright © 2012 Elsevier B.V. All rights reserved.)

In this study, a nanoscale protein chip is prepared by using an etched polystyrene (PS) template. This protein chip can be directly used for immunoassay, with the help of Surface Enhanced Raman Scattering (SERS) spectra. Some glass slides submerged in aldehyde is initially prepared, modified with antibodies, human immunoglobulin G (IgG). Then PS arrays are self-assembled on these slides with the Langmuir-Blodgett method. The PS template pattern is transferred to the human IgG substrate using an etching process-slides are exposed to O(2) plasma for 90s. The PS nanoparticles are then washed away using phosphate buffered saline solution. Next, the slides are dipped into bovine serum albumin solution to ensure that the anti IgG would bond only to the human IgG. At this moment, a patterned protein chip is obtained. When used for protein detection, the protein chip could be immersed into labeled specificity antigen solution. Here we chose fluorescein isothiocyanate anti-human IgG. After washing, only bonded antigens remain. Fluorescence microscopy and SERS is used to characterize the samples. The SERS spectra intensity shows liner correlation with the concentration of anti-human IgG. All the experiments are conducted in a phosphate buffered saline solution at 37°C for 2 h., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Surface-enhanced Raman scattering (SERS) of 4,4'-azopyridine (AZPY) on silver foil substrate was measured under 1064nm excitation lines. Density-functional theory (DFT) methods were used to calculate the structure and vibrational spectra of models such as Ag-AZPY, Ag(4)-AZPY and Ag(6)-AZPY complexes with B3LYP/6-31++G(d,p)(C,H,N)/Lanl2dz(Ag) basis set. The Raman bands of AZPY were identified on the ground of analog computation of potential energy distribution. The calculated spectra of Ag(4)-AZPY and Ag(6)-AZPY models were much approximated to the experimental results than that of Ag-AZPY model. The DFT results showed that the angles between two pyridyl rings keep 0 degrees from AZPY to Ag-AZPY, Ag(4)-AZPY and Ag(6)-AZPY model. The energy gaps between the HOMO and LUMO changed from 363 to 1140nm for AZPY-Ag complexes according to the DFT results. An conclusion was conceived that chemical enhancement mechanism may play an important role in the SERS of AZPY on silver substrate.