Adsorption mode of neurotensin family peptides onto a colloidal silver surface: SERS studies

Kinetensin (KN) and its amino acids 1–8 fragment ([des‐Leu⁹]KN), neuromedin N (NMN), and xenopsin (XP) and its two analogs (human XP‐1/xenin‐8 and XP‐2) belong to the neurotensin family of peptides and are known to stimulate the growth of human tumors. In this work, we report surface‐enhanced Raman scattering (SERS) studies of these peptides and discuss their structures, orientation, and mode of adsorption onto a colloidal assembly of apparently randomly adhering Ag spheres with diameters of approximately 20 – 25 nm. We show that small alternations in both the amino acid composition and tertiary structure, which induce striking biological in vitro, were responsible for the observed spectroscopic changes. Copyright © 2012 John Wiley & Sons, Ltd.     

Potential‐induced Raman behavior of individual (R)‐di‐2‐naphthylprolinol molecules on a Ag‐modified Ag electrode

The applicability of surface‐enhanced Raman spectroscopy is demonstrated to probe the adsorption behavior of individual molecules on a Ag electrode. High‐quality SERS spectra of (R)‐di‐2‐naphthylprolinol (DNP) were obtained from ultradilute solutions (10⁻¹² M ) on the Ag‐nanoparticle‐modified Ag electrode, which is attributed to the high electromagnetic (EM) effect of the SERS‐active system as well as to the strong adsorption and interaction of DNP molecules with Ag. The stable SERS spectra present remarkable potential dependence, which gives evidence for the behavior of individual DNP molecules on the Ag surface. Based on statistical analysis for the probability of DNP molecules located in ‘hot spots’, we propose an SERS mechanism for individual molecules in the electrode system, in combination with the hot‐spot model and orientation of the probe molecules. Copyright © 2010 John Wiley & Sons, Ltd.     

Nanogaps in 2D Ag‐nanocap arrays for surface‐enhanced Raman scattering

The surface‐enhanced Raman scattering substrate of Ag–Ag nanocap arrays are prepared by depositing Ag film onto two‐dimensional (2D) polystyrene colloidal nanosphere templates. When the original colloidal arrays are used as the substrate for Ag deposition, surface‐enhanced Raman scattering (SERS) enhancements show the strong size‐dependence behaviours. When O₂‐plasma etched 2D polystyrene templates are used as the substrate for Ag deposition to form nanogaps, the gap sizes between adjacent Ag nanocaps from 5 to 20 nm generate even greater SERS enhancements. When SiO₂ coverage is deposited to isolate the Ag nanocaps from the neighbours, the SERS signals are enhanced more. The significant SERS effects are due to the coupling between Ag nanocaps controlled by the distance, which enhances the local electric‐field intensity. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering‐based approach for DNA detection at low concentrations via polyvinyl alcohol‐protected silver grasslike patterns

A simple method is demonstrated to detect DNA at low concentrations on the basis of surface‐enhanced Raman scattering (SERS) via polyvinyl alcohol‐protected silver grasslike patterns (PVA‐Ag GPs) grown on the surface of the common Al substrate. By the SERS measurements of sodium citrate and thymine, the PVA‐Ag GPs are shown to be an excellent SERS substrate with good activity, stability and reproducibility. With the use of the tested molecule of thymine, the enhancement factor of the PVA‐Ag GPs is up to ~1.4 × 10⁸. The PVA‐Ag GPs are also shown to be an excellent SERS substrate with good biocompatibility for DNA detection, and the detection limit is down to ~10⁻⁵ mg/g. Meanwhile, the assignations of the Raman bands and the adsorption behaviors of the DNA molecules are also analyzed. In this work, the geometry optimization and the wavenumber analysis of adenine–Ag and guanine–Ag complexes for the ground states are performed using density functional theory, B3LYP functional and the LanL2DZ basis set. The transition energies and the oscillator strengths of adenine–Ag and guanine–Ag for the lowest six singlet excited states were calculated by using the time‐dependent density functional theory method with the same functional and basis set. The results show that the charge transfer in the adenine–Ag and guanine–Ag complexes should be the chemical factor for the SERS of the DNA molecules. Lastly, this method may be employed in large‐scale preparation of substrates that have been widely applied in the Raman analysis of DNA because the fabrication process is simple and inexpensive. Copyright © 2011 John Wiley & Sons, Ltd.     

Identification of two Ag‐2,2′:6′,2″‐terpyridine surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis: evidence for chemical mechanism contribution to SERS of Ag(0)–tpy

Measurement and interpretation of the excitation wavelength dependence of surface‐enhanced Raman scattering (SERS) spectra of molecules chemisorbed on plasmonic, e.g. Ag nanoparticle (NP) surfaces, are of principal importance for revealing the charge transfer (CT) mechanism contribution to the overall SERS enhancement. SERS spectra, their excitation wavelength dependence in the 445–780‐nm range and factor analysis (FA) were used for the identification of two Ag‐2,2′:6′,2″‐terpyridine (tpy) surface species, denoted Ag⁺–tpy and Ag(0)–tpy, on Ag NPs in systems with unmodified and/or purposefully modified Ag NPs originating from hydroxylamine hydrochloride‐reduced hydrosols. Ag⁺–tpy is a spectral analogue of [Ag(tpy)]⁺ complex cation, and its SERS shows virtually no excitation wavelength dependence. By contrast, SERS of Ag(0)–tpy surface complex generated upon chloride‐induced compact aggregate formation and/or in strongly reducing ambient shows a pronounced excitation wavelength dependence attributed to a CT resonance (the chemical mechanism) contribution to the overall SERS enhancement. Both the resonance (λ_exc = 532 nm) and off‐resonance (λ_exc = 780 nm) pure‐component spectra of Ag(0)–tpy obtained by FA are largely similar to surface‐enhanced resonance Raman scattering (λ_exc = 532 nm in resonance with singlet metal to ligand CT (¹ MLCT) transition) and SERS (λ_exc = 780 nm) spectra of [Fe(tpy)₂]²⁺ complex dication. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of adsorption mode of new B2 bradykinin receptor antagonists onto colloidal Ag substrate

In this paper, the surface‐enhanced Raman scattering (SERS) spectra of the potent B₂ bradykinin receptor antagonists, [D‐Arg⁰,Hyp³,Thi^5,8,L‐Pip⁷]BK, Aaa[D‐Arg⁰,Hyp³,Thi^5,8,L‐Pip⁷]BK, [D‐Arg⁰,Hyp³,Thi⁵,D‐Phe⁷,L‐Pip⁸]BK, and Aaa[D‐Arg⁰,Hyp³,Thi⁵,D‐Phe⁷,L‐Pip⁸]BK, were measured when immobilized onto a colloidal assembly of apparently randomly adhering Ag spheres with diameters of approximately 20 – 25 nm. The observed SERS bands corresponding to different vibrational modes of the molecule, attached to or near Ag, and the variations in these bands resulting from competitive interactions of the functional groups of the peptides with the SERS‐active Ag surfaces were analyzed in this study. Briefly, it was shown that Pip, in generally in vertical orientation, and Thi, in the edge‐on position, relative to the colloidal Ag surface interacted with this surface through their lone electron pairs on the nitrogen and sulfur atoms, respectively. The imide bond of the X‐Pro peptide linkage and the guanidine group of Arg were involved in the adsorption process. In addition, it was demonstrated that the specific differences in the amino acid sequences slightly influenced the mode of adsorption. For example, Aaa in Aaa[D‐Arg⁰,Hyp³,Thi^5,8,L‐Pip⁷]BK and Aaa[D‐Arg⁰,Hyp³,Thi⁵,D‐Phe⁷,L‐Pip⁸]BK and D‐Phe (vertical with respect to the colloidal Ag surface) in [D‐Arg⁰,Hyp³,Thi⁵,D‐Phe⁷,L‐Pip⁸]BK, and Aaa[D‐Arg⁰,Hyp³,Thi⁵,D‐Phe⁷,L‐Pip⁸]BK assisted in the adsorption of these peptides onto the colloidal Ag particles. To discuss these spectral alterations due to the different surface adsorption mechanisms of these peptides, the spectral changes were analyzed according to the adsorption process and Fourier‐transform‐Raman spectra. Copyright © 2013 John Wiley & Sons, Ltd.     

B2 bradykinin receptor antagonists: adsorption mechanism on electrochemically roughened Ag substrate

In this paper, the surface‐enhanced Raman scattering (SERS) spectra of the potent B₂ bradykinin receptor antagonists, [D‐Arg⁰,Hyp³,Thi^5,8,L‐Pip⁷]BK, Aaa[D‐Arg⁰,Hyp³,Thi^5,8,L‐Pip⁷]BK, [D‐Arg⁰,Hyp³,Thi⁵,D‐Phe⁷,L‐Pip⁸]BK, and Aaa[D‐Arg⁰,Hyp³,Thi⁵,D‐Phe⁷,L‐Pip⁸]BK, were measured when immobilized onto a highly specific electrochemically roughened SERS‐active Ag substrate characterized by the formation of a 50 – 150 nm Ag islands on its surface. The observed SERS bands corresponding to different vibrational modes of the molecule, attached to or near Ag, and the variations in these bands resulting from competitive interactions of the functional groups of the peptides with the SERS‐active Ag surfaces and reorientation occurring over time of adsorption were analyzed in this study. Copyright © 2012 John Wiley & Sons, Ltd.     

Identification of berberine in ancient and historical textiles by surface‐enhanced Raman scattering

The highly fluorescent natural dye berberine can be easily identified in microscopic textile samples by surface‐enhanced Raman spectroscopy employing citrate‐reduced Ag colloid. The ordinary Raman (OR) and SERS spectra of berberine are presented and discussed in the light of a DFT calculation. Using FT‐Raman and FT‐SERS we could reliably compare relative intensity shifts and investigate the adsorption geometry of berberine on Ag nanoparticles. The significant enhancement in the FT‐SERS spectrum of the out‐of‐plane ring system bending deformation mode at 729 cm⁻¹ relative to a group of in‐plane vibrations at around 1500 cm⁻¹ was interpreted as evidence of a ‘flat‐on’ adsorption geometry. SERS was successfully used to identify berberine in silk fiber samples coated with colloidal Ag following a pretreatment with HCl vapor. The SERS method allowed us to detect berberine in a microscopic sample of a single silk fiber from a severely degraded and soiled 17th Century Chinese textile fragment. Copyright © 2007 John Wiley & Sons, Ltd.     

Silver‐decorated carbon nanotube networks as SERS substrates

We report on investigations upon a surface‐enhanced Raman scattering (SERS) substrate produced from a two‐dimensional single‐walled carbon nanotube (SWNT) network decorated with Ag nanoparticles. Using the strong and unique Raman spectrum of SWNTs as a reference, the SWNT/Ag nanostructure can be considered to provide two regions: one with an ultrasensitive SERS response for single‐molecule SERS (SMSERS) study; and another with uniform SERS enhancement over an area of several square millimeters for general SERS measurements. We report the appearance of an anomalous Raman feature at around 2180 cm⁻¹ in the high‐sensitivity region which exhibits the characteristics of SMSERS. The SERS performance of the uniform area was characterized using pyridine vapor adsorbed onto the substrate. The presence of the SWNT/Ag nanostructure enhanced the Raman intensity by over seven orders of magnitude, a factor comparable to or exceeding that obtained on SERS substrates reported by other groups. The results indicate great potential to produce highly sensitive, uniform SERS substrates via further fine‐tuning of the nanostructure. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman scattering of L‐tryptophan enhanced by surface plasmon of silver nanoparticles: vibrational assignment and structural determination

Vibrational bands of L ‐tryptophan which was adsorbed on Ag nanoparticles (∼10 nm in diameter) have been investigated in the spectral range of 200–1700 cm⁻¹ using surface‐enhanced Raman scattering (SERS) spectroscopy. Compared with the normal Raman scattering (NRS) of L ‐tryptophan in either 0.5 M aqueous solution (NRS‐AS) or solid powder (NRS‐SP), the intensified signals by SERS have made the SERS investigation at a lower molecular concentration (5 × 10⁻⁴ M ) possible. Ab initio calculations at the B3LYP/6‐311G level have been carried out to predict the optimal structure and vibrational wavenumbers for the zwitterionic form of L ‐tryptophan. Facilitated with the theoretical prediction, the observed vibrational modes of L ‐tryptophan in the NRS‐AS, NRS‐SP, and SERS spectra have been analyzed. In the spectroscopic observations, there are no significant changes for the vibrational bands of the indole ring in either NRS‐AS, NRS‐SP, or SERS. In contrast, spectral intensities involving the vibrations of carboxylate and amino groups are weak in NRS‐AS and NRS‐SP, but strong in SERS. The intensity enhancement in the SERS spectrum can reach 10³–10⁴‐fold magnification. On the basis of spectroscopic analysis, the carboxylate and amino groups of L ‐tryptophan are determined to be the preferential terminal groups to attach onto the surfaces of Ag nanoparticles in the SERS measurement. Copyright © 2008 John Wiley & Sons, Ltd.     

Nanoporous Ag–GaN thin films prepared by metal‐assisted electroless etching and deposition as three‐dimensional substrates for surface‐enhanced Raman scattering

Three‐dimensional (3D) nanoporous gallium nitride (PGaN) scaffolds are fabricated by Pt‐assisted electroless hydrofluoric acid (HF) etching of crystalline GaN followed by in situ electroless deposition of Ag nanostructures onto the interior surfaces of the nanopores, yielding a large surface area substrate for surface‐enhanced Raman scattering (SERS). The resulting 3D SERS‐active substrates have been optimized by varying reaction parameters and starting material concentration, exhibiting enhanced Raman signals 10–100× more intense than either (1) sputtered Ag‐coated porous GaN or (2) Ag‐coated planar GaN. The increase in SERS signal is attributed to a combination of the large surface area and the inherent transparency of PGaN in the visible spectral region. Overall, Ag‐decorated PGaN is a promising platform for high sensitivity SERS detection and chemical analysis, particularly for reaction and metabolic products that can be trapped inside the highly anisotropic nanoscale pores of PGaN. The potential of this sampling mode is illustrated by the ability to acquire Raman spectra of adenine down to 5 fmol. Additionally, correlated SERS and laser desorption/ionization mass spectrometry spectra can be acquired from same sample spot without further preparation, opening new possibilities for the investigation of surface‐bound molecules with substantially enhanced information content. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman and surface‐enhanced Raman studies of α‐aminophosphinic inhibitors of metalloenzymes

Here, we report the nature of new di‐α‐amino (L¹–L³) and α‐amino‐α‐hydroxyphosphinic (L⁴–L⁶) acids, which are considered potential inhibitors of the aminopeptidase N, adsorbed on a colloidal silver surface by means of surface‐enhanced Raman scattering (SERS) spectroscopy. In order to reveal the adsorption mechanism of these species from their SERS spectra, Fourier‐transform Raman (FT‐RS) spectra of these nonadsorbed molecules were measured. By examining the enhancement, shift in wavenumbers, and changes in breadth of the SERS bands due to the adsorption process, we revealed that the tilted compounds interact with the colloidal silver substrate mainly through the benzene ring, amino group, and phosphinic moiety in the following way. The benzene ring of L² and L³ is ‘standing up’ on the colloidal silver surface, and the C N bond is almost vertical to it, while the tilt angle between the O PO bond and this surface is greater than 45°. On the other hand, for L¹, L⁴, and L⁵, the aromatic ring and C N bond are arranged more or less tilted, and the tilt angle between the O PO bond and the silver substrate is smaller than 45°. The elongation of the bond to the benzene ring, the L⁶ case, produces an almost horizontal orientation of the benzene ring and the O PO bond on the silver nanoparticles. For these ligands, the complement inhibition IC₅₀ tested in vitro using porcine kidney leucine aminopeptidase was correlated mainly with the behavior of the O PO and C CH N fragments on the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Detection and quantitative analysis of carbendazim herbicide on Ag nanoparticles via surface‐enhanced Raman scattering

Carbendazim (MBC) is a fungicide widely used in agriculture, and there are serious concerns regarding the health risks that could be caused by this fungicide. Here, we explore its ultrasensitive detection by surface‐enhanced Raman scattering (SERS). First, to obtain maximum SERS signal, the adsorption of the target molecule onto metallic surface is essential. Therefore, we study the adsorption of the MBC onto the nanoparticle surface by SERS under different experimental conditions, such as different synthesis methods of nanoparticle, variable excitation wavelength, and fungicide concentration with the aim to detect MBC at low concentrations. Experiments are carried out with three kinds of colloidal nanoparticles: Ag and Au reduced by citrate and Ag reduced by hydroxylamine. However, mainly Ag colloids are highly efficient in the SERS detection of MBC. In addition, theoretical calculations of MBC Raman spectrum and that of the surface complex are used to help with the understanding the mechanisms responsible for the interaction between MBC and Ag. Ultraviolet–visible absorption spectroscopy showed displacement to the red of the plasmon resonance of Ag colloid in the presence of MBC. Copyright © 2015 John Wiley & Sons, Ltd.     

Role of Phe‐D5 isotopically labeled analogues of bradykinin on elucidation of its adsorption mode on Ag,Au, and Cu electrodes. Surface‐enhanced Raman spectroscopy studies

Raman (RS), surface‐enhanced Raman scattering (SERS), electrochemistry, and isotopic effect methods were used to characterize selective adsorption of two isotopically labeled bradykinin analogues, [(Phe‐D₅)⁵]BK and [(Phe‐D₅)⁸]BK, a hormone which is known to be involved in small‐cell and non‐small‐cell lung carcinoma and prostate cancer. The investigated analogues contain Phe residue, at position 5 or 8 in the amino acid sequence, substituted by Phe‐D₅ (five protons of L‐phenylalanine ring substituted by deuterium). [(Phe‐D₅)⁵]BK and [(Phe‐D₅)⁸]BK were immobilized onto electrochemically roughened Ag, Au, and Cu electrode surfaces under different applied electrode potentials (−1.000 V to 0.200 V) in an aqueous solution containing 0.01 M phosphate buffer (pH = 7.0) and 0.1 M Na₂SO₄. Based on the analyses of the spectral profiles in the 920 – 1050 cm⁻¹ spectral range, specific conclusions were drawn with respect to the Phe⋅⋅⋅metal interactions and changes in the interaction that occurred when the adsorption conditions were varied. Copyright © 2013 John Wiley & Sons, Ltd.     

Visible light response of silver 4‐aminobenzenethiolate and silver 4‐dimethylaminobenzenethiolate probed by Raman scattering spectroscopy

Silver thiolate is a layered compound with a Raman spectrum that is known to change with time, becoming the same as the surface‐enhanced Raman scattering (SERS) spectrum of the parent thiol molecule adsorbed on Ag nanoparticles. On this basis, the Raman scattering characteristics of silver 4‐aminobenzenethiolate (Ag‐4ABT) compounds were investigated to determine whether certain peaks that are identifiable in the SERS spectrum of 4‐aminobenzenethiol (4‐ABT) but absent in its normal Raman spectrum were also apparent in the Ag salt spectrum. For comparative purposes, the Raman scattering characteristics of silver 4‐dimethylaminobenzenethiolate (Ag‐4MABT) were also examined. Raman spectra acquired while spinning the sample were typified by only a₁‐type vibrational bands of Ag‐4ABT and Ag‐4MABT, whereas in the static condition, several non‐a₁‐type bands were identified. The spectral patterns acquired in the static condition were similar to the intrinsic SERS spectra of 4‐ABT or 4‐dimethylaminobenzenethiol (4‐MABT) adsorbed on pure Ag nanoparticles. Notably, the CH₃ group vibrational bands were observable for Ag‐4MABT irrespective of the sample rotation. In addition, no decrease in intensity during irradiation with a visible laser was observed for any of the bands, suggesting that no chemical conversion actually took place in either 4‐ABT or 4‐MABT. The preponderance of evidence led to the conclusion that the non‐a₁‐type bands observable in the SERS spectra must be associated with the chemical enhancement mechanism acting on the Ag nanoparticles. The chemical enhancement effect was more profound at 514.5 nm than at 632.8 nm, and was more favorable for 4‐ABT than 4‐MABT at both wavelengths. Copyright © 2012 John Wiley & Sons, Ltd.     

Adsorbed states of substituted α‐aminophosphinic acids on a silver electrode surface: comparison with a colloidal silver substrate

We investigated the interfacial structures of various aromatic (each compound contains one or two phenyls) di‐α‐amino ( L¹ – L³ ) and α‐amino‐α‐hydroxyphosphinic ( L⁴ – L⁶ ) acids immobilized onto an electrochemically roughened silver electrode surface in an aqueous solution using surface‐enhanced Raman scattering (SERS). These structures were compared to those on a colloidal silver surface to determine the relationship between adsorption strength and geometry. The presence of an enhanced ν_19a ring band in the SERS spectra of L⁶ , L² , and L³ on the electrode indicated that the benzene rings of those molecules interact with the electrode surface through localized CC bond(s). We observed significant band broadening of the benzene ring modes for all α‐hydroxyphosphinic acids on both substrates, except for L¹ deposited onto the electrode surface. This suggests the possibility of direct interaction between the ring and Ag, although the benzene ring–surface π overlap is weaker for the colloidal silver than for the Ag electrode. The downward shift in wavenumber and alternations in the enhancement of a ν₁₂ ring band indicate a general increase of tilt angle on both silver substrates in the order L³ < L⁴ < L⁵ < L⁶ . The altered enhancement of the bands due to the vibrations of the  NH₂ and O PO fragments, a finding observed on both silver substrates, strongly suggests that the groups interact with different strength and geometry with these substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering of protoberberine alkaloids

Quaternary protoberberine alkaloids are a class of natural dyes characterized by bright colors ranging from yellow to orange. As they present a strong fluorescence emission, their analysis by Raman spectroscopy is limited to specific techniques such as Fourier transform (FT)‐Raman and spectral shift Raman techniques such as shifted subtracted Raman difference spectroscopy (SSRDS) and shifted excitation Raman difference spectroscopy (SERDS). In a previous article, we successfully used surface‐enhanced Raman scattering (SERS) in the analysis of the alkaloid dye berberine in an ancient textile. The examination of the Raman and SERS spectra of berberine in combination with density functional theory (DFT) calculations indicated a flat adsorption geometry of the molecule on the Ag surface. In this article we extend that work to the study of related protoberberine alkaloids, palmatine, jatrorrhizine, and coptisine. The same adsorption geometry as in berberine was deduced. We found that the four alkaloids, although minimally different in their chemical structures, could be differentiated by the position of marker bands. Those bands are the most enhanced ones in the SERS spectra, which appear in the 700–800 cm⁻¹ region. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering characteristics of CuO : Mn/Ag heterojunction probed by methyl orange: effect of Mn2+ doping

Interest in the synthesis of hybrid substrates for surface‐enhanced Raman scattering (SERS) has surged recently. Hereof, in the present work, a hybrid SERS substrate CuO : Mn/Ag heterojunction has been synthesised. To accomplish this, the nanostructred Ag island film and CuO : Mn nanoparticles are synthesised by vacuum thermal evaporation method and sol–gel method respectively, and thereafter, a heterojunction between the CuO : Mn and Ag is fabricated by adsorption of CuO : Mn (10^‐3 m in ethanol) on Ag island film. Further, the SERS sensitivity of CuO : Mn/Ag heterojunctions has been studied by probing methyl orange. We observed that with Mn‐doping in the lattice of CuO, the SERS signal is enhanced considerably because of ferromagnetic ordering in CuO : Mn. DFT/B3LYP/6‐311 G(d, p) method is used to calculate the energy of HOMO and LUMO level of methyl orange. Copyright © 2016 John Wiley & Sons, Ltd.     

SERS study of Ag nanoparticles electrodeposited on patterned TiO2 nanotube films

In this work, Ag nanoparticles (NPs) were deposited on patterned TiO₂ nanotube films through pulse‐current (PC) electrodeposition, and as a result patterned Ag NPs films were achieved. Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X‐ray diffraction (XRD) were used, respectively, to study the morphology, uniformity, and phase structure of the patterned Ag NP films. The size and density of the as‐deposited Ag NPs could be controlled by changing the deposition charge density, and it was found that the patterned Ag NP films produced under a charge density of 2.0 C cm⁻² gave intense UV–vis and Raman peaks. Two‐dimensional surface‐enhanced Raman scattering (SERS) mapping of rhodamine 6G (R6G) on the patterned Ag NP films demonstrated a high‐throughput, localized molecular adsorption and micropatterned SERS effect. Copyright © 2010 John Wiley & Sons, Ltd.     

Charge‐transfer contributions in surface‐enhanced Raman scattering from Ag,Ag2S and Ag2Se substrates

The degree of charge‐transfer in Ag–4‐mercaptopyridine (Mpy) and Ag₂S–4‐Mpy systems is investigated by use of surface‐enhanced Raman spectroscopy (SERS). Ag₂S and Ag₂Se nanoparticles are prepared on the basis of the former formation of Ag nanoparticles to make the SERS analytical objects comparable. We utilize the intensity of the non‐totally symmetric modes (either b₁ or b₂) as compared with the totally symmetric a₁ modes to measure the degree of charge‐transfer. We find ~25% of charge‐transfer contribution for Ag–4‐Mpy, whereas 81 ~ 93% for Ag₂S–4‐Mpy. It means that the charge‐transfer resonance contribution dominates the overall enhancement in SERS of Ag₂S–4‐Mpy. Energy level diagram is applied to discuss the likely charge‐transfer transition between Ag, Ag₂S, Ag₂Se and 4‐Mpy. This article may point out the link among the three main resonance sources and could enable some insights into the electronic pathways available to the metal‐molecule and semiconductor‐molecule systems. Copyright © 2012 John Wiley & Sons, Ltd.