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A series of non‐spherical metallic Au and bimetallic core@shell AuAg nanoparticles (NPs) have been synthesized for SERS improvements. The bimetallic core@shell AuAg NPs were obtained through a controlled overgrowth of an Ag shell onto the surface of two types of non‐spherical Au NPs, used as seeds, Au nanooctaheda (Au NOc) and Au nanotriangles (Au NTs). This Ag overgrowth was able to produce bimetallic core@shell structures such as nanocubes and nanopyramids, respectively. Transmission electron microscopy (TEM) was used to determine the particle size and particle morphology for metallic and bimetallic NPs, and energy‐dispersive X‐ray (EDX) elemental mapping analysis confirmed the core@shell structure of the bimetallic NPs. The plasmonic absorption bands exhibited for each nanosystem were observed by UV–vis spectroscopy. The concentration of Au and Ag in the bimetallic systems was determined by inductively coupled plasma mass spectrometry (ICP‐MS). After synthesis and characterization, p‐aminothiophenol (PATP) was used as a model analyte to investigate the surface‐enhanced Raman spectroscopy (SERS) capabilities of the synthesized metallic and bimetallic nanosystems. In PATP, a dimerization reaction to 4,4′‐dimercaptoazobenzene (DMAB) is produced when it is adsorbed onto the surface of certain noble metals. This SERS analysis was performed at 10−4 M of PATP and by using two different laser wavelengths (532 and 785 nm) in all cases. In this context, we were able to detect the dimerization reaction of PATP to DMAB only for the bimetallic structures and under the 532 nm laser line. Moreover, we have found that the dimerization capacity also depends on the nanoparticle morphology. [ABSTRACT FROM AUTHOR]

Optical absorption spectra of para-aminothiophenol in n-hexane and methanol solutions have been obtained. The calculation has been carried out using the TDDFT B3LYP/6-311+G(d,p) method taking into account the polarizable continuum model of the electronic spectra of the p-aminothiophenol molecule in n-hexane and its hydrogen-bonded complex with two methanol molecules in a methanol solution. Based on these calculations, the main absorption bands are interpreted and it is shown that the second excited singlet state is formed by a π → σ* electronic transition, which makes a significant contribution to the first absorption band of p-aminothiophenol in these solutions. [ABSTRACT FROM AUTHOR]

Metal nanoparticles trapped in a biopolymer composite due to electrical conductivity properties improve electrochemical sensors with biomedical and environmental applications. The study aims are to design a novel molecularly imprinted polymer (MIP) composite based on magnetic graphene oxide (Fe3O4@GO) modified silica (SiO2) and gold nanoparticles (AuNPs) to electrochemical detect serotonin (5-hydroxytryptamine, 5-HT). A suitable amount of 5-HT is effective on motivational functions and the environment because it is a serotonergic neurotransmitter. But the desired nanocomposite may have a relatively low recognition, therefore must be in choosing the type of functional monomer be careful. In this regard, the design of the electrochemical sensor began by synthesis of Fe3O4@GO-SiO2@AuNPs nanocomposite. Then, MIP electropolymerization was carried out by using p-aminothiophenol (PATP)-functionalized Fe3O4@GO-SiO2@AuNPs nanocomposite in the presence of 5HT as a template molecule. Electrochemical polymerization of MIP nanocomposite was developed using cyclic voltammetry (CV) and the electrochemical properties of 5-HT were studied use differential pulse voltammetry (DPV) technology in the 5HT solution. After optimization of preparation and measurement conditions on the designed sensor, the 5HT concentration range is 0.1 μM to 10 μM linearly, and the detection limit was 1 × 10-5 μM (S / N = 3). The wide concentration range and low detection limit were presented metal nanoparticles functionalized MIP with appropriate functional monomer have a great effect on the performance of the sensor. Furthermore, PATP-functionalized metal nanoparticles increase the conductivity and recognition of the prepared MIP electrochemical sensor to the quantification of 5-HT in biological samples with high selectivity and recovery.

Surface acoustic wave (SAW) devices are extensively used to detect various gaseous chemicals, owing to their wireless passive potential and single-signal display. However, the sensitivity, selectivity, and long response time of the sensitive layers limit their use in detecting explosive gases. In this study, we developed a 2,4,6-trinitrotoluene (TNT) gas sensor based on the SAW device with GO/PDEA/AuNR/PATP nanocomposites. The GO/PDEA/AuNR/PATP-SAW sensor recorded a considerable negative frequency shift (−70.67 kHz) in detecting 80 ppm TNT at 25 °C/20 RH %, thus enabling the detection of 40 ppb to 80 ppm TNT with the limit of detection as low as 40 ppb (−3.02 kHz). Short response/recovery time (40 ppb: 6.2/11.8 s) with good cycling stability and selectivity were achieved. The high performance of the GO/PDEA/AuNR/PATP-SAW sensor is attributed to its large specific surface area, roughness, and porosity. The oxygen-containing and electron-rich amino groups of the GO/PDEA/AuNR/PATP provide many active sites for adsorbing TNT gas. The primary sensing mechanism is the mass and electrical load of the nanocomposite in TNT gas. It has an optimum thickness of 380 nm and room temperature as the optimum operating temperature. Therefore, this study would serve as a good basis for the research and development of next-generation acoustic gas-phase explosive sensors. [ABSTRACT FROM AUTHOR]

Electrochemical reactions on nanostructured noble electrodes have received much attention, however, the reaction mechanism and reaction kinetics are still difficult to be studied. Probe molecule can give an insight to the investigation of electrochemical reactions on noble electrodes with nanostructures. In this paper, the electrochemical process of p-aminothiophenol (PATP) adsorbed on the gold electrode was studied by electrochemical cyclic voltammetry and surface-enhanced Raman spectroscopy (SERS). Here, we used one-step sodium citrate reduction method (Frens method) to synthesize gold nanoparticles, which are used to construct the nanostructured gold electrode. The Raman electrolytic cell used was based on the traditional three-electrode electrolytic cell. The gold electrode was used as the working electrode (WE), the saturated calomel electrode (SCE) as the reference electrode (RE), and the platinum wire (Pt) as the counter electrode (CE). After the careful pretreatment of the gold electrode surface, the cell was assembled and placed on the platform of the XploRa instrument to get started. With the assistance of potentiostat, the SERS spectra at different potentials were acquired and combined together, a so-call electrochemical surface-enhanced Raman spectroscopic (EC-SERS) experiment. In a 0.05 mol⋅-1 sulfuric acid solution (pH = 1), an irreversible oxidation peak was found in the cyclic voltammogram, which is considered to correspond to the oxidation of the PATP molecule. The oxidation mechanism is proposed by combination of previous work in literature, and it is pointed out that the PATP molecule was initially transformed into cationic radical. Then, this cationic radical coupled with the PATP molecule to an intermediate NPQDH2, and finally electrochemically oxidized to 4'-mercapto-N-phenylquinone diamine (NPQD). On the basis of this mechanism, the surface coverage of PATP on the electrode surface was calculated and the coverage value was found to be larger at the nanostructured electrode due to the modification of gold nanoparticles than that of general gold electrodes. In the following, the electrochemical oxidation product was characterized by the EC-SERS spectra. Finally, we experimentally and theoretically studied the electrochemical oxidation kinetics of PATP on the gold nanoparticle-modified gold electrode (Au NPs@Au). The apparent reaction rate constant k and transfer coefficient α of PATP were calculated by electrochemical linear sweeping voltammetry and theoretical simulation, respectively, finding that the cationic radical formation step is the rate-limiting step. We believe that this work will no doubt stimulate the basic research of PATP on gold electrodes consisting of nanostructures and provide a guide to electrochemical kinetic research in other metal-adsorbate systems. [ABSTRACT FROM AUTHOR]

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We have synthesized Ag7 nanoclusters via a facile one‐pot procedure with p‐aminothiophenol (PATP) as the ligand. The chemical component of this Ag7 cluster is determined to be Ag7(C6H6NS)7H+ by high‐resolution electrospray mass spectrometry, where a few fragment peaks are also observed such as [Ag7(C6H6NS)4H3Na]+. For this PATP‐protected Ag7 cluster, we have conducted a Raman investigation to probe in the intracluster interactions and find an essentially different Raman feature from that the nascent PATP ligand, pertaining to photo‐assistant catalytic conversion of PATP to p,p'‐dimercapto azobenzene (DMAB). Utilizing density‐functional‐theory (DFT) calculations, we have performed natural population analysis, natural bond orbital analysis, and electron density difference analysis to fully demonstrate the intracluster interactions between Ag7 clusters and the ligand. What is interesting is that the protection ligand PATP helps stabilize the Ag7 metallic core, and in turn, the metal core Ag7 catalyzes the protection ligands giving rise to N─N coupling reaction. On this basis, we have proposed a reaction pathway on a basis of DFT calculations to provide further insights into the reaction mechanism of PATP‐to‐DMAB conversion at the presence of the Ag7 clusters. [ABSTRACT FROM AUTHOR]

• The six-electron reduction of PATP to PNTP by hot electrons occurs on Au, Ag and Cu nanoparticles. • The reactions are enhanced by ligands due to an increase of the metal nanoparticles' Fermi level. • Ligand-enhanced hot electron reduction provides a way to improved light-to-chemical energy conversion. Hot carriers (electrons and holes) generated from the decay of localized surface plasmon resonances can take a major role in catalytic reactions on metal nanoparticles. By obtaining surface enhanced Raman scattering (SERS) spectra of p-aminothiophenol as product of the reduction of p-nitrothiophenol by hot electrons, different catalytic activity is revealed here for nanoparticles of silver, gold, and copper. As a main finding, a series of different ligands, comprising halide and non-halide species, are found to enhance product formation in the reduction reaction on nanoparticles of all three metals. A comparison with the standard electrode potentials of the metals with and without the ligands and SERS data obtained at different electrode potential indicate that the higher catalytic activity can be associated with a higher Fermi level, thereby resulting in an improved efficiency of hot carrier generation. The concept of such a ligand-enhanced hot electron reduction provides a way to make light-to-chemical energy conversion more efficient due to improved electron harvesting. [ABSTRACT FROM AUTHOR]

Plasmon-mediated electrochemistry is an emerging area of interest in which the electrochemical reactions are enhanced by employing metal nanostructures possessing localized surface plasmon resonance (LSPR). However, the reaction efficacy is still far below its theoretical limit due to the ultrafast relaxation of LSPR-generated hot carriers. Herein, we introduce p -hydroxythiophenol (PHTP) as a molecular cocatalyst to significantly improve the reaction efficacy in plasmon-mediated electrochemical oxidation of p -aminothiophenol (PATP) on gold nanoparticles. Using electrochemical techniques, in situ Raman spectroscopy, and theoretical calculations, we elucidate that the presence of PHTP improves the hot hole-mediated electrochemical oxidation of PATP by 2-fold through the trapping of plasmon-mediated hot electrons. In addition, the selectivity of PATP oxidation could also be modulated by the introduction of PHTP cocatalyst. This tactic of employing molecular cocatalyst can be drawn out to endorse various plasmonic electrochemical reactions because of its simple protocol, high efficiency, and high selectivity.

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. [ABSTRACT FROM AUTHOR]

A flexible and effective substrate for surface-enhanced Raman spectroscopy (SERS) detection has been developed by dip coating of triangular silver nanoplates (TSNPs) onto cotton fabrics. The morphology, chemical composition and crystalline structure of the coated cotton fabrics were characterized by scanning electron microscope (SEM), ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectroscopic (XPS) and X-ray diffraction (XRD), respectively. These results confirmed the presence and well dispersion of the TSNPs on the surface of cotton fabrics. p -aminothiophenol (PATP) has been used as the probe molecule to evaluate the performance of the coated cotton fabrics as a flexible SERS substrate, and the PATP in diluted solutions can be detected with the concentration as low as 10 −8  M. The results indicate that the TSNPs-coated fabrics exhibit sensitive SERS signals with excellent reproducibility and stability. The flexible SERS substrate has been demonstrated to rapidly detect carbaryl pesticides on fruits. [ABSTRACT FROM AUTHOR]

A micro-structured gold surface, consisting of a periodic square-based anti-pyramidal array (Klarite) with a smooth boundary surface on which silver nanoparticles (diameter: 60 nm) were deposited, produced an active surface enhanced Raman scattering substrate. With p-aminothiophenol as a probe molecule, the Raman activity of the micro-structured surface was compared before and after deposition of the silver nanoparticles. Experimental results show that the Raman spectra on the silver/p-aminothiophenol/Klarite structure is stronger than that on the silver/p-aminothiophenol/gold film and the Raman spectra on the silver/p-aminothiophenol/gold film is stronger than that on silver/p-aminothiophenol, p-aminothiophenol/Klarite structure, p-aminothiophenol/gold film, which is confirmed by numerical simulations. A similar result is obtained with crystal violet as test molecule. [ABSTRACT FROM AUTHOR]

Electrocatalytic hydrogen evolution reaction (HER) is receiving increasing attention as an effective process to produce clean energy. The commonly used precious metal catalysts can be hybridized with semiconductors to form heterostructures for the improvement of catalytic efficiency and reduction of cost. It will be promising to further improve the efficiency of heterostructure-based nanocatalysts in electrocatalytic and photocatalytic HER using a simple and effective method. Herein, we improve the efficiency of Au/TiO 2 in electrocatalytic and photo-electrocatalytic HER by selectively adsorbing p -aminothiophenol (PATP) molecules. The PATP molecules are adsorbed on the gold surface by using a simple solution-based method and favor the charge separation at the Au-TiO 2 interface. We also compare the PATP molecules with other thiophenol molecules in the enhancement of electrocatalytic HER. The PATP-induced enhancement in electrocatalysis is then further investigated by density functional theory (DFT) calculations, and this enhancement is attributed to a reduction in Gibbs energy of adsorbed hydrogen after surface adsorption of PATP molecules. This work provides a simple, cost-effective, and highly efficient approach to improve the electrocatalytic and photo-electrocatalytic efficiency of Au/TiO 2 , and this approach could be easily extended to other heterostructure-based nanocatalysts for performance enhancement and may be used in many other catalytic reactions.

Aminothiophenol/Au(111) has been adopted as an exemplary model in plasmonics research, including surface-enhanced Raman spectroscopy, due to its high plasmonic-induced spectral-signal enhancement. The present work was aimed at clarifying whether aminothiophenol on Au(111) is chemically stable in the absence of any photo- and plasmonic-induced effects. Briefly, first-principles calculations were employed to track the detailed mechanism of oxidative coupling of p-aminothiophenol (PATP) to its azo-adduct with an N = N bond, i.e., p, p′-dimercaptoazobenzene (DMAB). Our results show the following: first, in the presence of adsorbed O, PATP fractures its N-H bond and transfers the hydrogen to a nearby oxygen. This pathway is more favorable than the transfer of H to Au, but the activation barrier of 0.9 eV is still too high for the reaction to occur in the absence of thermal-, photo-, or plasmonic-activation. If this bar can be lifted, two such dehydrogenated PATP can couple themselves to form an adduct with a N-N bond, i.e., p, p′-dimercaptohydroazobenzene (DMHAB), and this reaction is exoergic with an energy barrier of 0.57 eV. Again, this step is slow in the absence of moderate thermal activation or photo-/plasmonic-activation. Finally, dehydrogenation of DMHAB gives the azo-adduct of DMAB, and this reaction is spontaneous, with no energy barrier. [ABSTRACT FROM AUTHOR]

Electrocatalytic hydrogen evolution is an important approach to produce clean energy, and many electrocatalysts (e.g., platinum) are developed for hydrogen production. However, the electrocatalytic efficiency of commonly used metal catalysts needs to be improved to compensate their high cost. Herein, the electrocatalytic efficiency of platinum nanoparticles (PtNPs) in hydrogen evolution is largely improved via simple surface adsorption of sub-monolayer p-aminothiophenol (PATP) molecules. The overpotential goes down to 86.1 mV, which is 50.2 mV lower than that on naked PtNPs. This catalytic activity is even better than that of 20 wt.% Pt/C, despite the much smaller active surface area of PATP-adsorbed PtNPs than Pt/C. It is theoretically and experimentally confirmed that the improved electrocatalytic activity in hydrogen evolution can be attributed to the change in electronic structure of PtNPs induced by surface adsorption of PATP molecules. More importantly, this strategy can also be used to improve the electrocatalytic activity of palladium, gold, and silver nanoparticles. Therefore, this work provides a simple, convenient, and versatile method for improving the electrocatalytic activity of metal nanocatalysts. This surface adsorption strategy may also be used for improving the efficiency of many other nanocatalysts in many reactions., (© 2023 Wiley-VCH GmbH.)

Nanoscale noble metals can exhibit excellent photochemical and photophysical properties, due to surface plasmon resonance (SPR) from specifically collective electronic excitations on these metal surfaces. The SPR effect triggers many new surface processes, including radiation and radiationless relaxations. As for the radiation process, the SPR effect causes the significant focus of light and enormous enhancement of the local surface optical electric field, as observed in surface-enhanced Raman spectroscopy (SERS) with very high detection sensitivity (to the single-molecule level). SERS is used to identify surface species and characterize molecular structures and chemical reactions. For the radiationless process, the SPR effect can generate hot carriers, such as hot electrons and hot holes, which can induce and enhance surface chemical reactions. Here, we review our recent work and related literature on surface catalytic-coupling reactions of aromatic amines and aromatic nitro compounds on nanostructured noble metal surfaces. Such reactions are a type of novel surface plasmon-enhanced chemical reaction. They could be simultaneously characterized by SERS when the SERS signals are assigned. By combining the density functional theory (DFT) calculations and SERS experimental spectra, our results indicate the possible pathways of the surface plasmon-enhanced photochemical reactions on nanostructures of noble metals. To construct a stable and sustainable system in the conversion process of the light energy to the chemical energy on nanoscale metal surfaces, it is necessary to simultaneously consider the hot electrons and the hot holes as a whole chemical reaction system. [ABSTRACT FROM AUTHOR]

[Display omitted] • An innovative molecular imprinted electrochemical sensor was fabricated. • The sensor is based on AuNPs coated on NiS 2 NS/BC. • AuNPs were used to facilitate polymerization of p-ATP. • Molecular imprinted based sensor was used for the determination of FAV. • Advantages are high selectivity and sensitivity, good reproducibility, and acceptable stability. A molecularly imprinted electrochemical sensor was fabricated for sensitive and selective detection of anti-COVID 19 drug favipiravir (FAV). The sensor is based on the synthesis of biomass-derived carbon (BC) and nickel disulfide nanospheres (NiS 2 NS), which were used to decorate glassy carbon electrode (GCE). Then, the gold nanoparticles (AuNPs) were electro- deposited on the surface of NiS 2 NS/BC/GCE to enhance conductivity, increase electron transfer, and aid polymerization of p-aminothiophenol (p-ATP) functional monomer. The fabrication steps were characterized using different morphological and electrochemical techniques. Variables affecting the formation of molecularly imprinted layers and the determination of FAV were optimized. Under optimum conditions, the oxidation current (Ipa) was increased upon addition of FAV in the range of 0.42–1100 nM with a limit of detection (LOD, S/N) of 0.13 nM. The as-fabricated sensor possesses several advantages such as high sensitivity and selectivity, good reproducibility, and acceptable stability. Furthermore, the proposed molecularly imprinted –based electrochemical sensor was efficiently applied for the determination of FAV in tablets and human serum samples with recoveries % of 99.2 to 102.1 % and RSDs % in the range of 2.4–3.2 %, which confirms the reliability of the sensor to detect FAV in different matrices. [ABSTRACT FROM AUTHOR]

p-Aminothiophenol (pATP) functionalized multi-walled carbon nanotubes (MWCNTs) have been demonstrated as an efficient pH sensor for living cells. The proposed sensor employs gold/silver core-shell nanoparticles (Au@Ag NPs) functionalized MWCNTs hybrid structure as the surface-enhanced Raman scattering (SERS) substrate and pATP molecules as the SERS reporters, which possess a pH-dependent SERS performance. By using MWCNTs as the substrate to be in a state of aggregation, the pH sensing range could be extended to pH 3.0∼14.0, which is much wider than that using unaggregated Au@Ag NPs without MWCNTs. Furthermore, the pH-sensitive performance was well retained in living cells with a low cytotoxicity. The developed SERS-active MWCNTs-based nanocomposite is expected to be an efficient intracellular pH sensor for bio-applications. [ABSTRACT FROM AUTHOR]

We investigated a gap mode plasmon under an attenuated total reflection (ATR) configuration toward realization of near-field Raman spectroscopy with a single molecule sensitivity and spatial resolution. Additional enhancement in Raman scattering at a nanogap was obtained by a coupling of a propagating surface plasmon (PSP) of Ag films on a prism, and a gap mode between Ag films and Ag nanoparticles (AgNPs). Immobilization of AgNPs on Ag films through thiol-SAM slightly up-shifted the resonance angle of a PSP, which broadened the reflectivity dip owing to an increased out-coupling of a PSP. Raman enhancement factor at a nanogap increased with decreasing surface coverage of AgNPs, albeit the enhancement factor averaged over illuminated area in Ag films decreased, ensuring the largest enhancement factor in tip-enhanced Raman scattering. This is due to increased efficiency for a PSP excitation at lower coverage of AgNPs in consistent with that in theoretical evaluation using finite difference time domain calculations. A gap mode under an ATR configuration was applied to elucidate a plausible photochemical reaction of p-amino thiophenol (PATP) adsorbed on Ag films on a prism. Spectral changes in Raman scattering under laser illumination were observed for PATP with a deuterated amino group, but suppressed by a dimethyl amino group owing to steric hindrance, supporting the photochemical dimerization. [ABSTRACT FROM AUTHOR]

Abstract: To exploit a gap mode plasmon in flocculates of metal nanoparticles most efficiently, the interaction between adsorbed chemical species and metal nanostructures were adjusted. We successfully formed flocculates of Ag nanoparticles (AgNPs) using electrostatic interaction between dissociated p-mercaptobenzoic acid (PMBA), protonated p-aminothiophenol (PATP) and their counter ions (Mn+, Xm−), as well as van der Waals force between neutral PMBA, PATP and AgNPs. Detailed adsorbed state of PMBA and PATP in addition to trapped counter ions was characterized using enormous SERS enhancement in a flocculation method. [Copyright &y& Elsevier]

Highlights: [•] Aliphatic aminothiol can induce the aggregation of citrate stabilized silver sol. [•] The p-aminothiophenol induced aggregation of Ag colloid has electrostatic nature. [•] In diluted aqueous solutions, p-aminothiophenol (p-ATP) oxidizes depending on the pH. [•] Oxidized form of p-ATP is necessary for “b 2-mode enhancement” in the SERS spectrum. [•] Azo-bridge formation seems to be responsible for the “b 2-mode enhancement.” [ABSTRACT FROM AUTHOR]

There has been a surge of interest in the surface-enhanced Raman scattering (SERS) of p-aminothiophenol (PATP), since its SERS spectra are dependent on the measurement conditions. However, there is a dispute over the origin of the so-called b2 modes in SERS spectrum of PATP recently. Some researchers propose that these bands come from selective chemical enhancement, while others conclude that these bands are due to the ag modes of p,p'-dimercaptoazobenzene (DMAB) produced from PATP by surface photoreaction. To solve this problem, we have studied the SERS spectra of PATP on Au and Ag nanoparticles by in situ measurement under various conditions. The results proved that the b2 modes are not due to PATP but due to the ag modes of DMAB. The key of the method is to ensure the SERS spectra taken from the same point in reduplicative measurements. The result showed that the stable SERS spectrum of PATP was essentially from DMAB. The reversibility of the PATP SERS spectra in previous studies is due to the variety of the measurement points, which is in nature of different PATP conversions to DMAB under different conditions. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the effect of the temperature of the plasmonic substrate on the surface enhanced Raman scattering of p-aminothiophenol adsorbed onto a particulate film of gold nanoparticles-decorated polystyrene nanospheres. The results demonstrated that temperature induces important modifications in the overall spectral signature of the charge transfer bands, which are consistent with the generation of a new molecular species. Moreover, the analysis of the shape of the vibrational band at 1078cm−1 assigned to the >C−S mode, which is enhanced by electromagnetic mechanism, reveals the co-existence of two distinct bands at 1071 and 1078cm−1, assignable to p,p’-dimercaptoazobenzene and p-aminothiophenol, respectively. [Copyright &y& Elsevier]

Abstract: In this paper, small-sized and highly dispersed Ag nanoparticles (NPs) supported on graphene nanosheets are fabricated via a strategy for etching a copper template with Ag+. Firstly, big-sized Cu NPs are supported on graphene, and then the small-sized and highly dispersed Ag NPs are supported on graphene by replacement reaction, mainly making use of graphene passing electrons between Cu and Ag+. The graphene used in the experiment is prepared by in situ self-generating template and has good dispersion, excellent crystallinity and little defects. Thus, in the process of Ag/graphene synthesis, there is no any intervention of surfactant, which ensures that SERS activity sites have not been passivated. And, the little defects of graphene benefit the excellent conductivity of graphene and ensured the replacement reaction between Cu and Ag+. The obtained material exhibits significant high-quality and distinctive SERS activity. Especially, a serial new peak of p-aminothiophenol (PATP) is observed, this is suggested two reasons: one is “surface geometry” of the PATP on small-sized Ag NPs and another is the charge-transfer between Ag and graphene. [Copyright &y& Elsevier]

Abstract: In the present work, we study the adsorption of p-aminothiophenol (p-ATP) on gold nanorods (GNRs) using localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS) spectroscopies, as function of molecular concentration and pH values in solution. The LSPR spectra reveal the adsorption of p-ATP molecules onto the ends of GNRs. We address the intriguing case that has recently emerged in SERS literature regarding the interpretation of p-ATP SERS spectrum. Apart from typical electromagnetic bands of p-ATP, the aggregation of GNRs at basic pH revealed the appearance in SERS spectra of some extra bands, which can be assigned to the formation of p,p′-dimercaptoazobenzene (DMAB) through chemical transformation of p-ATP on metallic substrates. We correlate the SERS results with theoretical simulations of electromagnetic enhancement of Raman signal for individual and assembled GNRs by employing the Finite-Difference Time-Domain (FDTD) method. [Copyright &y& Elsevier]

Abstract: The surface of a gold (Au) electrode was modified with p-aminothiophenol (p-ATP) and well-packed monomolecular layers through a sulfur–Au bond were formed. Functionalization of Au–ATP self-assembled monolayer (SAM) with 4-formylphenylboronic acid (BA) via Schiff''s base formation, through in situ method, to fabricate Au–ATP–BA electrode is presented. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were used to investigate the changes in electrode behavior after each assembly step. The surface pKa value of the Au–ATP–BA SAM electrode was estimated by CV and EIS. In the presence of sugar, the terminal groups of Au–ATP–BA SAM electrode can react with sugar by forming the phenylboronate esters of sugar on the surface of the electrode; the pKa values for the Au–ATP–BA SAM electrode in the presence of different sugars (D-glucose, D-fructose, and D-mannose) were obtained. The fabricated electrode can be used as a novel biosensor for determining sugars on the basis of the change in i p of the Fe(CN)6 3−/4− ion in the presence of sugars. The biosensor exhibited excellent performance in determining D-glucose, D-fructose, and D-mannose, with low detection limits, wide linear ranges and good sensitivities. [Copyright &y& Elsevier]

Abstract: Nano-SiO2/p-aminothiophenol (PATP) film was fabricated by self-assembly and electrodeposition methods. The immobilization and hybridization of DNA on the nano-SiO2/PATP film were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS was applied to label-free detection of the target DNA according to the increase of the electron transfer resistance (R et) of the electrode surface after the hybridization of the probe DNA with the target DNA. This DNA electrochemical biosensor showed its own performance of simplicity, good stability, fine selectivity and high sensitivity, and was successfully applied to the detection of the PAT gene sequences by a label-free EIS method. The dynamic detection range was from 1.0×10−11 to 1.0×10−6 mol/L 20-base sequence of the PAT gene, with the detection limit of 1.5×10−12 mol/L. This DNA sensor has a good ability of recognizing single- or double-base mismatched DNA sequence with the complementary DNA sequence. [Copyright &y& Elsevier]

Abstract: In this paper, an approach for fabricating an active surface-enhanced Raman scattering (SERS) substrate is adopted. This approach is based on the assembling of silver nanoparticles film on gold substrate. Rhodamine 6G (R6G) and p-aminothiophenol (p-ATP) were used as probe molecules for SERS experiments, showing that this new active substrate has sensitivity to SERS response. Tapping-mode atomic force microscopy (AFM) was also used to investigate the surface morphology following the fabricating process of the active SERS substrate, which showed that large quantities of silver nanoparticles were uniformly coated on the substrate. [Copyright &y& Elsevier]

[Display omitted] • Boron was determined with a novel GC/AuNPs/poly(p -aminothiophenol) sensor electrode. • Indirect voltammetric method for boron made use of signal suppression of mannitol. • Mannitol-H 3 BO 3 complexation enabled estimation at mg L−1 B-level without interference. • Boron was recovered from real seawater, hand sanitizer gel and pyrotechnic formulation. • The developed method was statistically validated against a spectrophotometric method. In this study, a glassy carbon electrode (GCE) modified with gold nanoparticles (AuNPs) and coated with electropolymerized p -aminothiophenol (p -ATP) was used as a modified electrode (GC/AuNPs/PATP electrode) for the indirect electrochemical determination of boron (B) using boric acid-mannitol complexation. The developed electrode showed good electroactivity for B determination. Firstly the current intensity of mannitol was measured, then B (as H 3 BO 3) was added to the medium and the unreacted mannitol was measured. The decrement in current intensity was recorded against B concentration to build linear calibration curves within the range of 5–50 mg L−1 of B using square wave voltammetry (SWV), and the oxidation peak potential of mannitol was observed at 0.97 V. The limit of detection (LOD) and limit of quantification (LOQ) were 1.43 mg L−1 and 4.77 mg L−1, respectively. Boron (5 mg L−1) was determined with quantitative recovery in the presence of 100-fold concentration (except 5-fold for Fe3+) levels of the potentially interferent ions (Cl−, SO 4 2−, HCO 3 −, CO 3 2−, NO 3 2−, PO 4 3−, NH 4 +, Cu2+, Mg2+, Ca2+, Na+, K+, Fe3+) in water using the proposed SWV method. Fe3+ and Cu2+ interferences could be overcome with cation exchange resin removal. Additionally, boron was determined in synthetic and real seawater samples. The proposed SWV method was statistically validated against the spectrophotometric carmine method using seawater, antibacterial hand sanitizer gel and boron/potassium nitrate (BPN) pyrotechnic formulation. [ABSTRACT FROM AUTHOR]

Self-assembled monolayers (SAMs) on plasmonic substrates play a significant role applications of surface-enhanced Raman scattering (SERS). At the same time, localized surface plasmon resonances (LSPRs) can be employed for a broad range of plasmon-supported chemical modifications. Here, micropatterning using the derivatization of SAMs on gold nanosubstrates for rewritable SERS-based security labels or as the basis for sensing arrays functionalized with biomolecules is demonstrated using different plasmon-catalyzed reactions. The formation of 4,4'-dimercaptoazobenzene (DMAB) from p -aminothiophenol (PATP) as well as from p -nitrothiophenol (PNTP) and the reduction of PNTP to PATP are used to change the functionality of the substrate in specified positions. Employing LSPR, the reactions are started by illumination using visible laser light at a high intensity in a focal spot of a microscope objective and yield microscopic patterns of the reaction product. The obtained molecular patterns can be erased by other reactions, enabling different strategies for rewriting, encryption, or stepwise functionalization.

The search for cost-effective methods for the fabrication of sensitive and selective surface-enhanced Raman spectroscopy (SERS) substrates has led to recent studies exploring the incorporation of biopolymers as the supporting scaffold or nanostructure stabilizer. In this paper, we report on the effect of the enhancing nanostructure morphology on the SERS performance of chitosan-containing substrates. For this work, silver nanospheres, silver nanocubes, gold nanospheres, and gold nanorods were synthesized and fully characterized; then, SERS substrates were prepared using all of the morphologies and chitosan with varying concentrations and molecular weight to also test the effect of the biopolymer on the SERS effect. This work showed that the chitosan film allows for trapping of analyte molecules and thus, higher Raman intensities. It was found that the chitosan concentration plays an important role in this effect. The fabricated substrates showed minimum values of detected concentration between 10−4 and 10−9 M using p -ATP as probe molecule, depending on the nanostructure morphology used, showing that the silver nanocubes lead to a higher sensitivity and Raman intensities enhancement compared to the other dispersions studied. Image 1 • SERS substrates were fabricated depositing plasmonic inks and chitosan layers on Al. • SERS performance of Ag spheres and cubes, and Au spheres and rods was tested. • SERS performance of low, medium, and high chitosan molecular weights were tested. • The SERS substrate based on Ag cubes allowed a LOD of 10−9 M for p -ATP. [ABSTRACT FROM AUTHOR]

Accurate and early diagnosis of zearalenone (ZEN) is particularly significant to the food safety. Herein, we propose an ionic liquid assisted self-assembly molecular imprinting strategy for ZEN based on ionic liquid functionalized boron-doped ordered mesoporous carbon -gold nanoparticles composite (BOMC-IL-Au NPs). During the composite synthesis, increased well-dispersed and uniform Au NPs are deposited on the surface of IL modified BOMC, due to the strong electrostatic interaction between AuCl 4 − and positively charged IL. For molecular imprinting, the BOMC-IL-Au NPs/GCE is immersed into p-aminothiophenol (p-ATP) solution and template solution in turn. Thus, the mercapto group contained p-ATP self-assembles on the Au NPs. Subsequently, the template molecules self-assemble onto the composite to form dense template layer, because of the hydrophobic interaction, π-π and hydrogen bond between template and IL/or p-ATP. After electropolymerization, the template layer is embedded into the p-ATP polymer membrane and produces lots of imprinting sites. Hence, the obtained sensor exhibits high sensitivity and selectivity. Under the optimal conditions, zearalenone can be quantified from 5 × 10−4 to 1 ng mL−1 with the low detection limit of 1 × 10−4 ng mL−1, by using [Fe(CN) 6 3-/4- probe and square wave voltammetry. This strategy can also be employed to construct sensors for the detection of other substances. An ionic liquid assisted self-assembly molecular imprinting sensor was developed for the detection of zearalenone. The sensor exhibited high sensitivity, selectivity and low detection limit. Image 1 • An ionic liquid assisted self-assembly molecular imprinting strategy was developed. • Ionic liquid improves the deposition of well-dispersed and small Au NP. • The monomer self-assemble on the composite benefit the electrochemical imprinting. • The templates assembled on the composite make the imprinted site density increase. • The sensor exhibited high sensitivity, selectivity and low detection limit. [ABSTRACT FROM AUTHOR]

In this study, various concentrations of p-aminothiophenol doped 3-glycidoxypropyltrimethoxysilane based sol-gel matrices (PATP-GPTMS) are prepared through hydrolysis and condensation reactions. The prepared PATP-GPTMS sol-gel is applied on the polished copper (Cu) surface (PATP-GPTMS/Cu) by self-assembly technique. The surface profile of resultant coatings are characterized by important analytical tools such as Fourier transform infra-red (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and stylus profilometer. The surface morphologies of coatings are acquired by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM) techniques. The FT-IR and XPS results revealed the linking of PATP and thiol monolayer on Cu surface in 0.1 M PATP-GPTMS/Cu coating. Further, the corrosion protection ability of PATP-GPTMS/Cu coatings in 3.5% sodium chloride (NaCl) medium are studied by common electrochemical tools. The electrochemical impedance spectroscopy (EIS) results showed that PATP-GPTMS/Cu coating exhibit improved corrosion resistance than the undoped GPTMS/Cu coating. The maximum corrosion inhibition efficiency of 96.39% is achieved on 12 h self-assembly technique based sol-gel coating of 0.1 M PATP-GPTMS/Cu by polarization method. All the results exposed that, the PATP-GPTMS/Cu coating enhanced the corrosion protection of Cu in aqueous 3.5% NaCl medium. Unlabelled Image • PATP-GPTMS based sol-gel matrices were prepared for corrosion protection of Copper. • XPS results revealed the doping of PATP and thiol layer on Cu surface in coating. • The maximum protection efficiency of 96.39% was achieved by 0.1 M PATP-GPTMS/Cu. [ABSTRACT FROM AUTHOR]