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A simple and efficient enantioselective discrimination method, especially the chirality-label-free discrimination method, for the recognition of chiral small molecules with high resolution and wide applicability has been urgently desired. Herein, achiral Au/p-aminothiophenol (PATP) substrates were prepared to link the enantiomers via coupling reactions for constructing the enantioselective discrimination system. The resultant Au/PATP/enantiomer systems displayed charge-transfer (CT)-induced surface-enhanced Raman scattering (SERS) spectra that offered distinguishable information for the systems with different chirality. The differentiated spectral signal can be amplified by regulating the applied electrode potential, leading to great enantioselective discrimination performance. Moreover, the relationship between the discrimination performance and the potential-regulated CT process was revealed by SERS, which enabled an accurate and effective enantiomeric determination for various chiral molecules, including aromatic and aliphatic small molecules. The aliphatic molecule with the shorter chain was discriminated with a higher resolution, since the longer-chain molecule in the discrimination system may cause a change in the molecular electronic structure of the PATP. In addition, the aromatic chiral molecule can be distinguished easier than the aliphatic molecules, which means that the generation of the conjugation of electrons in the aromatic molecule-involved enantiomeric systems facilitates CT-induced SERS discrimination. Our work provides guidance for the design and development of an effective enantioselective discrimination strategy with high discrimination performance in diverse application fields. [ABSTRACT FROM AUTHOR]

Flavin mononucleotides (FMNs) and flavin adenine nucleotide (FAD) play vital roles in the electron-transfer processes in diverse enzymatic reactions. Owing to the isoalloxazine chromophore, flavins are easily detectable by surface-enhanced Raman spectroscopy (SERS), a surface-sensitive technique. However, the details of the adsorption of flavins on SERS-active materials have never been investigated. In this study, a comprehensive SERS analysis of flavins containing lumichrome and lumiflavin on silver nanoparticles was conducted. With the aid of density-functional-theory calculations, our results suggested that the flavin molecules were adsorbed on the silver nanoparticles via the N3 site of the isoalloxazine moiety, which had a stronger adsorption ability than the adenine moiety in the FAD. The SERS spectra of the flavins at different pH values also supported this conclusion. This study demonstrated the feasibility of SERS for the structural characterization of flavins, paving the way for the functional exploration of flavin-labeled detection sensors and flavoprotein researches. [ABSTRACT FROM AUTHOR]

A versatile surface-enhanced Raman scattering (SERS) assay has been established that can realize rapid and sensitive determination of sildenafil (SIL) and pioglitazone hydrochloride (PIO) adulteration in healthcare products. Metal–organic frameworks-silver nanoparticles (MOFs-AgNPs) with SERS activity were successfully prepared via in situ synthesis AgNPs on the MOFs surface. By virtue of the adsorptivity of MOFs, the MOFs-AgNPs could effectively concentrate the drug molecules on the electromagnetic enhancement areas of AgNPs. Moreover, the MOFs-AgNPs substrate exhibited more sensitive SERS activity than classical AgNPs with linear range of 1.0 × 10–7–1.0 × 10–5 mol L−1 for SIL and 8.0 × 10–7–3.0 × 10–5 mol L−1 for PIO and limit of detection (LOD) of 4.8 × 10–8 mol L−1 for SIL and 1.4 × 10–7 mol L−1 for PIO. The designed method realized the determination of SIL and PIO in commercial tablets and healthcare products with recoveries of 93.8–108.0% and 93.0–104.0%, respectively, with relative standard deviation (RSD) of 2.7–4.1% and 2.2–4.2%, respectively. The present system displayed little interference effect on determination. This work provides a multifunctional route for the determination of other drugs via the SERS technology. [ABSTRACT FROM AUTHOR]

A rapid, ultrasensitive and selective method has been established to determine antithyroid drugs [propylthiouracil (PTU) and methimazole (MTZ)] by surface-enhanced Raman scattering (SERS). Silver nanoparticles (AgNPs) were synthesized by reduction of silver nitrate (AgNO3) with sodium alginate (SA) and were used as SERS substrates. Through optimization of the SERS conditions, including the volume of SA-protected AgNPs solution, pH of Britton–Robinson (BR) buffer solution and concentration of NaCl solution, linear responses were obtained for PTU and MTZ in the concentration ranges of 3.02 × 10−9–1.06 × 10−5 mol L−1 and 1.21 × 10−9–1.21 × 10−5 mol L−1, respectively. By the present method, the limits of detection (LODs) for the determination of PTU and MTZ were as low as 1.58 × 10−10 mol L−1 and 2.97 × 10−11 mol L−1. The method was successfully applied for the determination of PTU and MTZ in real samples. The recovery of PTU and MTZ from actual samples ranged between 97.20 and 104.80%, with relative standard deviations (RSDs) less than 3.63%. [ABSTRACT FROM AUTHOR]

A versatile and robust chiral discrimination strategy for small aromatic compounds is of significant importance in multidisciplinary fields. However, most current methods lack either the sufficient sensitivity for recognizing the chirality of the target molecules or their molecular specificity information. We have developed a versatile and chiral‐label‐free surface‐enhanced Raman scattering (SERS)‐based chiral discrimination sensing system for small aromatic molecules, where the molecular structural specificity and enantioselectivity can be given synchronously in a single SERS spectrum. More than 10 types of chiral aromatic molecules were successfully identified by using this system. This work has enormous potential for recognizing chiral products effectively in sophisticated systems, especially in the fields of chiral synthesis and chiral catalysis. [ABSTRACT FROM AUTHOR]

A surface-enhanced Raman scattering (SERS) method is described for the determination of prazosin (PRH) and losartan (LOS). Silver nanoparticles modified with β-cyclodextrin (CD-S-Ag NPs) were prepared and serve as a sensitive SERS substrate. β-CD is both a reductant for silver ions and a host molecule that binds the analytes which leads to strong SERS enhancement. The method has distinct features: (a) The linear response extends from 0.1 to 60 μM for PRH, and from 1.0 to 100 μM for LOS; (b) the respective limits of detection are as low as 15 nM and 0.92 μM; and (c) the specific SERS bands of PRH and LOS are located at 703 and 1298 cm−1 respectively. The method was successfully applied to the determination of PRH and LOS illegally added to healthcare products. The recovery of PRH and LOS from spiked samples ranges between 91.3 and 109.3%, and from 87.4 to 105.2%, respectively, both with relative standard deviation of <5%. [ABSTRACT FROM AUTHOR]

The interaction of cytochrome c (Cyt c) with cardiolipin (CL) is believed to play an important role in the initial events of apoptosis. Herein, we investigate the structural changes of CL‐bound Fe2+Cyt c and the correlation with Cyt c release through surface‐enhanced Raman spectroscopy (SERS) on nickel substrates. The SERS results together with molecular dynamics simulation reveal that Fe2+Cyt c undergoes autoxidation and a relatively larger conformational alteration after binding with CL, inducing higher peroxidase activity of Cyt c and higher permeability of the CL membrane compared with those induced by the Fe3+Cyt c. The proapoptotic activity and SERS effect of the Ni nanostructures allow the in situ study of the redox‐state‐dependent Cyt c release from isolated mitochondria, which reveals for the first time that the ferrous state of Cyt c most likely plays a more important role in triggering apoptosis. [ABSTRACT FROM AUTHOR]

A remarkable enhancement of Raman scattering is achieved by submicrometer‐sized spherical ZnO superstructures. The secondary superstructures of ZnO particles with a uniform diameter in the range of 220–490 nm was formed by aggregating ca. 13 nm primary single crystallites. By engineering the superstructure size to induce Mie resonances, leading to an electromagnetic contribution to the SERS enhancement. Meanwhile, a highly efficient charge‐transfer (CT) contribution derived from the primary structure of the ZnO nanocrystallites was able to enhance the SERS signals as well. The highest Raman enhancement factor of 105 was achieved for a non‐resonant molecule by the synergistic effect of CT and Mie resonances. The Mie resonances scattered near‐field effect investigated in the present study provides not only an important guide for designing novel SERS‐active semiconductor substrates, but also a coherent framework for modelling the electromagnetic mechanism of SERS on semiconductors. [ABSTRACT FROM AUTHOR]

Interfacial charge transfer (CT) is of interest owing to its effect on the performance of molecular photovoltaic (PV) devices. The characteristics and structures of interfacial materials, such as TiO2 nanoparticles (NPs) in some solar cells, are employed to adjust the CT process. In this study, three kinds of interfacial systems, including a solar cell‐like TiO2‐Ag‐ p‐mercaptopyridine (MPY)‐ iron phthalocyanine (FePc) system, are compared to investigate the interfacial CT process using surface‐enhanced Raman scattering (SERS) spectroscopy. The SERS results show the significance of TiO2 NPs in the system on altering the direction and path of the interfacial CT, which is closely associated with the CT enhancement contribution to SERS in such an interfacial system. SERS spectroscopy is expected to be a promising technique for the exploration and estimation of the interfacial CT behavior in PV devices, which may further extend the applications of SERS in the field of solar cells. [ABSTRACT FROM AUTHOR]

We report on the analysis of dendritic crystals present in the dark spot areas of blue‐and‐white Ming porcelains. Using Raman spectroscopy and scanning electron microscopy equipped with energy dispersive spectrometer, we were able to evidence Mn‐rich spinels. Small Mn‐based spinel crystals being highly sensitive to laser‐induced heating, we identified proper working conditions, avoiding excessive heating and damage. Local temperatures during Raman measurements were deduced from Stokes/anti‐Stokes intensity ratios. By analysing the behaviour of the A1g mode of Mn‐rich spinels, we were able to identify phases ranging from jacobsite‐like to hausmannite‐like compounds. Polarized Raman scattering was shown to provide a convenient means of discriminating between these two types of phases, as they display different symmetries. Inhomogeneities within the dendritic network, as evidenced by micro‐Raman measurements, highlight its gradual formation during the cooling phase of firing, depending of Fe3+ and Mn3+ availability. The presence of Mn‐based spinels is consistent with the use of a local Chinese Mn‐rich cobalt ore during the middle Ming Dynasty. [ABSTRACT FROM AUTHOR]

Charge-transfer processes of coupled semiconductor nanoparticles play an essential role in many application fields of semiconductors. It has been difficult to characterize the charge-transfer process between two semiconductor nanoparticles. Herein, we propose a new analytical tool with the chemical mechanism of Surface-Enhanced Raman Scattering (SERS) to provide information about the charge-transfer process in coupled semiconductor nanoparticle systems. In this work, two assemblies (namely, TiO2–MBA–CdS and CdS–MBA–TiO2) have been fabricated as models to explore the charge-transfer process between TiO2 and CdS nanoparticles by SERS. 4-MBA works as both the linker of these two semiconductors and the probe of SERS to reveal the charge-transfer process. Under excitations at 633 and 785 nm, which are far from the surface plasmon resonance of the CdS and TiO2 nanoparticles in the assemblies, there are some obvious changes in the peak intensities and peak shifts in the SERS spectra after introducing CdS to the TiO2/MBA system and TiO2 to the CdS/MBA system. The differences of the peak intensities in the TiO2–MBA–CdS and CdS–MBA–TiO2 assemblies show different charge-transfer processes. We have found that the dipole moment of a MBA molecule greatly influences the charge-transfer process between the TiO2 and CdS nanoparticles. [ABSTRACT FROM AUTHOR]

This paper reports the fabrication of gold‐patterned microarray chips for fast and ultrasensitive surface enhanced Raman scattering (SERS) detection of trace samples. By micro‐nano machining based on electron‐beam lithography, magnetron sputtering, and chemical modification, gold‐patterned microarray chips with hydrophilic and hydrophobic periodic structures are fabricated, and a polyethylene glycol (PEG) layer is coated on the surface of the gold well, making the chips long‐term stable. The hydrophilic surface of each gold well is surrounded by a hydrophobic layer, which makes the ultratrace sample amount for SERS measurement only 0.3 μl. In the detection of malachite green (MG), 4‐mercaptopyridine (4‐MPY), rhodamine 6G (R6G), and melamine, great enhanced SERS signals with the detection limit reaching nM level can be achieved due to the enrichment effect of the periodic structures and the hot‐spots generated between the sandwich structure built on the gold wells. Such gold‐patterned microarray chip is promising in fast and ultrasensitive SERS detection of various chemical and biological species with trace amount. Gold‐patterned microarray chips for fast and ultrasensitive surface enhanced Raman scattering detection of trace samples are reported. The hydrophilic surface of each gold well is surrounded by a hydrophobic layer, which makes the ultratrace sample amount for SERS measurement only 0.3 μl. Such gold‐patterned microarray chip is promising in fast and ultrasensitive SERS detection of various chemical and biological species with trace amount. [ABSTRACT FROM AUTHOR]

Phenformin hydrochloride (PHE), once used as a traditional anti-diabetic drug, has now been banned due to significant side effects. However, the phenomenon of the illegal addition of PHE to hypoglycemic healthcare products is still rampant. Thus, the detection of illegally added PHE is urgently needed. Surface-enhanced Raman scattering (SERS) is a promising candidate for this purpose, but the weak affinity between PHE and bare metal (Au or Ag) limits direct SERS detection of PHE. In this paper, we prepared Ag nanoparticles coated with β-cyclodextrin (AgNP@β-CD), which display the coffee-ring effect, that can be used for PHE sensing. β-CD-functionalized nanoparticles could capture the analyte and fix the molecular orientation in the hydrophobic cavity. The coffee-ring effect could improve the SERS effect through a higher concentration of the analyte, higher density of nanoparticles, and more hot spots. The SERS performance of the AgNP@β-CD substrate was characterized by using o-phenylenediamine dihydrochloride as a probe molecule. The excitation wavelength and pH value were optimized. A linear response for PHE detection is in the 7.0 × 10−8-1.0 × 10−6 mol L−1 concentration range, and the limit of detection is as low as 8.0 × 10−9 mol L−1. This AgNP@β-CD coffee-ring effect substrate was applied to the detection of PHE in healthcare products, with recoveries between 95.3 and 105.0% and relative standard deviations of less than 5.16%. It is anticipated that the AgNP@β-CD substrate will also have great potential for the monitoring of other aromatic drugs in healthcare products. [ABSTRACT FROM AUTHOR]

The illegal adulteration of natural healthcare products with chemical drugs can result in serious health risks for consumers. Thus there is an urgent need for a fast and precise detection method. In this research, sodium alginate (SA)-silver nanoparticles (AgNPs) were used as a substrate in surface-enhanced Raman scattering (SERS) for determining vardenafil and rosiglitazone maleate (ROS). Sodium alginate can not only reduce silver ions rapidly to AgNPs as reducing agents but can also protect AgNPs from aggregation by its use as a capping agent. The coffee ring effect has also been applied in this research to facilitate the separation and concentration of analytes. A prominent SERS enhancement can be obtained on the ring because of the electromagnetic mechanism. Both of the properties, including the use of SA and the coffee ring effect, make the method more sensitive in detecting the analytes compared to the classical AgNPs, SERS substrate which were produced using the reduction of silver nitrate with sodium citrate. The method displays a linear response for the determination of vardenafil and ROS in the 4.88–488 μg·mL−1 and 4.74–94.7 μg·mL−1 concentration ranges, and the limit of detection is as low as 1.63 μg·mL−1 and 2.20 μg·mL−1, respectively. The method was successfully applied to the detection of vardenafil and ROS in healthcare products, with recoveries between 91.52% to 107.1% and relative standard deviations of less than 4.31%. This method shows good potential for real applications. [ABSTRACT FROM AUTHOR]

Abstract: The differences between electromagnetic enhancement and chemical enhancement in surface‐enhanced Raman scattering (SERS) and their deep insight are very important and valuable for the explanation of spectral behaviors and the practical application of SERS technique. In this work, the typical semiconductor substrate TiO2 nanoparticles and noble‐metal substrate Ag colloid were selected as two representative SERS‐active substrates to investigate the differences between the electromagnetic (EM) mechanism and the charge‐transfer (CT) mechanism using 4‐mercaptobenzoic acid as probe molecule. The 4‐mercaptobenzoic acid molecules on two substrates exhibit the obvious differences in spectral behavior and signal intensity of SERS as well as the detectability, which can be attributed to the essential differences between the EM mechanism and the CT mechanism. The EM enhancement more depends on the behavior of the substrate, which more tends to be nonselective for the adsorbed molecules and their enhancement. The CT enhancement not only depends on the behavior of the substrate but also depends on the behavior of the adsorbed molecule due to the CT between substrate and molecule, which more tends to be selective for the adsorbed molecules and their enhancement. Moreover, it is also proved that the semiconductor (TiO2) SERS‐active substrate is characterized by the high stability and the recyclability. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) on organic–inorganic hybrid perovskites is explored and for the first time the SERS activity (EF ≥ 104) of the nanostructured CH3NH3PbBr3 has been proved. Here, the SERS profile displays high similarity with the normal Raman spectra and the enhancement mechanism is discussed according to the charge transfer contribution. [ABSTRACT FROM AUTHOR]

The Ag-Au compound nanostructure films with controllable patterns of Ag nanoparticle (NP) aggregates were fabricated. A strategy of two-step synthesis was employed toward the target products. Firstly, the precursor Au NP (17nm) films were synthesized as templates. Secondly, the Ag NPs (45nm) were deposited on the precursor films. Three types of Ag NP aggregates were obtained including discrete Ag NPs (discrete type), necklace-like Ag NP aggregates (necklace type), and huddle-like Ag NP aggregates (huddle type). The surface-enhanced Raman scattering (SERS) property was studied on these nanostructures by using the probing molecule of rhodamine 6G under the excitation laser of 514.5nm. Interestingly, the different types of samples showed different enhancement abilities. A statistical method was employed to assess the enhancement. The relative enhancement factor for each Ag NP was estimated quantitatively under the ratio of 1 : 25 : 18 for the discrete-type, necklace-type, and huddle-type samples at the given concentration of 10_8 mol/l. This research shows that the enhancement ability of each Ag NP is dependent on the aggregate morphology. Moreover, the different enhancement abilities displayed different limit detection concentrations up to 10-8, 10-11, and 10-9 mol/l, separately. The understanding of the relationship between the defined nanostructures and the SERS enhancement is very meaningful for the design of new SERS substrates with better performance. [ABSTRACT FROM AUTHOR]

A method for the investigation of photocatalytic degradation of organic molecules adsorbed on the surface of a compound nanostructure, silver nanoparticle (Ag NP) modified titania nanotubes (TiO 2 NTs), namely Ag/TiO 2 NTs, was proposed. The method was applied to the photocatalytic degradation of rhodamine 6G (R6G) dye molecules in order to determine its effectiveness. The surface-enhanced Raman scattering (SERS) technique was employed to monitor the photodegradation processes on these bifunctional nanostructures. The photocatalytic characteristic was attributed to the TiO 2 NTs; however, the SERS activity was caused by the Ag NPs. The Ag/TiO 2 NTs were able to detect R6G molecular probes with concentration down to 10 −8 M. The substrates could not only degrade the adsorbates, but also discard them off under ultraviolet irradiation owing to the high photocatalytic activity of TiO 2 . Thus, the substrates were able to self-clean and be reused for a new SERS detection cycle. The photodegradation and SERS results revealed that Ag/TiO 2 NTs acted as promising candidates for photocatalytic activity and SERS substrates; and exhibited high recyclability in the detection of organic molecules. The optimized SERS-active substrates were then employed to study the photodegradation of R6G. The photodegradation kinetics analysis was assessed by selecting the strongest SERS peaks which indicated that the kinetics of the photodegradation of R6G followed the pseudo-first order reaction. Finally, the results presented herein demonstrated that the fabricated Ag/TiO 2 NTs nanostructures were remarkably suitable as photocatalytically active SERS substrates. Further, the substrates could be effectively utilized for highly sensitive in situ monitoring of the surface photodegradation processes of organic molecules and could be recycled in a more environmentally sustainable manner. [ABSTRACT FROM AUTHOR]

Quantitative analysis of phosphate anions was achieved by measurement of “turn-off” SERS based on the first-layer effect of a chemical mechanism. More importantly, our results demonstrate that it is possible, by means of semiconductor-enhanced Raman scattering, to enhance the SERS sensing performance including stability and reproducibility. [ABSTRACT FROM AUTHOR]

In this paper, anatase and rutile TiO2 nanoparticles as well as their mixed crystal phase structure TiO2 nanoparticles were synthesized by a sol-hydrothermal method, and were served as active substrates for surface-enhanced Raman scattering (SERS) study. The results show that the 4-mercaptobenzoic acid probe molecules exhibit different degree SERS enhancements on the surface of different phase structure TiO2 nanoparticles. The mixed crystal structure TiO2 with an appropriate proportion of anatase and rutile phase is favourable to SERS enhancement of adsorbed molecules. These are mainly attributed to the contributions of the TiO2-to-molecule charge transfer mechanism and the mixed crystal effect. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Efficient and generic enantioselective discrimination of various chiral alcohols is achieved by using surface-enhanced Raman scattering (SERS) spectroscopy through charge-transfer (CT) contributions. The relative intensities of the peaks in the SERS spectra of a chiral selector are strongly dependent on the chirality of its surroundings. This highly distinct spectral discrepancy may be due to the tendency of chiral isomers to form intermolecular hydrogen-bonding complexes with the chiral selector in different molecular orientations, resulting in different CT states and SERS intensities of the adsorbates in the system. This study opens a new avenue leading to the development of novel enantiosensing strategies. A particular advantage of this approach is that it is label-free and does not employ any chiral reagents, including chiral light. [ABSTRACT FROM AUTHOR]

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

Glyphosate is one of the most commonly used and non-selective herbicides in agriculture, which may directly pollute the environment and threaten human health. A simple and effective approach to its detection is thus quite necessary. Surface-enhanced Raman scattering (SERS) spectroscopy was shown to be a very effective method to approach the problem. However, sensitivity in SERS experiments is quite low, caused by different orientation/conformation of the adsorbed molecules on the metal surface, which limit its detection by using SERS. In this paper, 2‒13C‒glyphosate (hereafter: 13–GLP) was designed as a model molecule for theoretical and experimental studies of the molecule structure. Vibrational modes were assigned based on the modeling results obtained at the B3LYP/6-311++G** level by density functional theory (DFT) calculations, which were performed to predict the FT‒IR and Raman spectra. Band downshifts were caused by 13C atom isotopic substitution with mass changed. Moreover, SERS spectra of 13–GLP by combining ninhydrin reaction on Ag NPs were obtained. Isotopic Raman shifts are helpful in identifying the components of each Raman band through vibrations across the molecular system. They are coupled by probe molecules and thus bind to the substrates, indirectly offering the opportunity to promote interactions with Ag NPs and reduce the complex equilibrium between different orientation/conformation of glyphosate molecules on the metal surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mg and/or Zn ions doped ZrO 2 NPs exhibited an excellent surface-enhanced Raman scattering (SERS) activity. • Numerous oxygen vacancies (O V) are generated during the doping process. • Mg/Zn-codoped ZrO 2 was used for determination of antibiotic drugs with high selectivity. Noble metal-based surface-enhanced Raman scattering (SERS)-active substrates have been developed for decades. However, nonreproducible aggregation and photoinduced molecular degradation limit the development of SERS technology. To overcome the shortcomings of noble metal-based SERS substrates, we designed ZrO 2 -based nanoparticles (NPs). By doping Mg and/or Zn ions into these ZrO 2 NPs, the SERS activity was significantly improved. Mg/Zn codoping of ZrO 2 resulted in a much higher oxygen deficiency, thereby providing a sufficient surface state energy (Ess) level to enable charge transfer (CT). The primary contribution for the Mg/Zn-codoped ZrO 2 was determined to be from the CT resonance effect, resulting in an enhancement factor (EF) as high as 104. Most importantly, the CT-induced enhancement of Raman scattering based on Mg/Zn-codoped ZrO 2 has already demonstrated some promising applications in highly sensitive quinolone antibiotic drug determination. Different kinds of quinolone antibiotic drugs can be easily identified and quantitatively analyzed with high sensitivity and reproducibility. [ABSTRACT FROM AUTHOR]

Abstract Norfloxacin (NFX) is an antibacterial agent belonging to the fluoroquinolone family of drugs, known to bind bovine serum albumin (BSA). Surface-enhanced Raman scattering (SERS) and fluorescence spectroscopy in combination with molecular docking were explored to investigate the binding interaction between NFX with Bovine serum albumin (BSA) at a physiological condition. This study focused on identifying the binding site and relevant interaction mechanisms between NFX and BSA. Spectrophotometric titration with molecular docking results demonstrated that the binding site of NFX on BSA was located in sub-domain IIA. The principle binding site was identified within a hydrophobic cavity which is surrounded by the residues Leu 197, Arg 198, Ser 201, Ala 209, Trp 213, Ser 343, Leu 346, Lys 350, Ser 453, Leu 480, Val 481, and the binding force was mainly hydrophobic interaction and hydrogen bond interaction. In addition, the absorptive orientation of the NFX molecule on the colloidal surface underwent a set of changes during the process of NFX binding to BSA. Graphical Abstract Unlabelled Image Highlights • The combination of SERS and molecular docking were explored to investigate the binding site of Norfloxacin on BSA. • The absorptive geometry of Norfloxacin with BSA on the self-assembled monolayer film was confirmed. • The detailed binding position and relevant interaction mechanism of Norfloxacin to BSA were obtained. [ABSTRACT FROM AUTHOR]

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]

Glyphosate is one of the most commonly-used and non-selective herbicides in agriculture, which may directly pollute the environment and threaten human health. A simple and effective approach to assessment of its damage to the natural environment is thus quite necessary. However, traditional chromatography-based detection methods usually suffer from complex pretreatment procedures. Herein, we propose a simple and sensitive method for the determination of glyphosate by combining ninhydrin reaction and surface-enhanced Raman scattering (SERS) spectroscopy. The product (purple color dye, PD) of the ninhydrin reaction is found to SERS-active and directly correlate with the glyphosate concentration. The limit of detection of the proposed method for glyphosate is as low as 1.43 × 10 − 8 mol·L − 1 with a relatively wider linear concentration range (1.0 × 10 − 7 -1.0 × 10 − 4 mol·L − 1 ), which demonstrates its great potential in rapid, highly sensitive concentration determination of glyphosate in practical applications for safety assessment of food and environment. [ABSTRACT FROM AUTHOR]

A new type of surface-enhanced Raman scattering (SERS) substrate was fabricated through the layer-by-layer self-assembly of silver nanoparticles (AgNPs, av. 45 nm in diameter) and porous gold nanoclusters/nanoparticles (AuNPs, av. 143 nm in diameter). The development of the porosity of the AuNPs was investigated, and successful SERS applications of the porous AuNPs were also examined. As compared with AgNP films, the enhancement factor of Ag-Au compound substrates is increased 6 times at the concentration of 10 −6 M. This additional enhancement contributes to the trace-amount-detection of target molecules enormously. The contribution is generated through the increase of the usable surface area arising from the nanoscale pores distributed three-dimensionally in the porous AuNPs, which enrich the adsorption sites and hot spots for the adsorption of probe molecules, making the developed nanofilms highly sensitive SERS substrates. The substrates were used for the detection of a physiological metabolite of urea molecules. The results reached to a very low concentration of 1 mM and exhibited good quantitative character over the physiological concentration range (1 ∼ 20 mM) under mimicking biophysical conditions. These results show that the prepared substrate has great potential in the ultrasensitive SERS-based detection and in SERS-based biosensors. [ABSTRACT FROM AUTHOR]

The antibiotic residue in animal source foods (milk, meat, etc.) is threatening people's health due to its abusing in livestock breeding more and more seriously. In this study, a simple and sensitive SERS method coupled with a two-step pretreatment process of sample was proposed for the residue detection of penicillin G (PENG) in real milk sample. It can be found that the two-step pretreatment process of sample is an essential procedure for the successful detection of PENG residue in milk, which can effectively avoid interference from other components in the sample and achieve the trace-level detection of PENG residue by SERS. Under the optimal test conditions, the limit of detection of PENG residue is 2.54×10 −9 mol/L (equal to 0.85 μg/kg), which is lower than the standard of the European Union (4 μg/kg). And, there is a good linear relationship (R 2 =0.9902) in the concentration range of 1.0×10 −8 ~1.0×10 −3 mol/L. By this method, the recovery of PENG residue ranges from 76% to 97% with relative standard deviation between 4.8% and 2.1%. The proposed SERS method can be effectively applied for determination of PENG residue in milk. [ABSTRACT FROM AUTHOR]

A very simple method for fabricating a superhydrophobic substrate was proposed. Zn foil was first polished and then immersed into an AgNO 3 solution to obtain a silver-coated surface (Zn/Ag), which resulted in the formation of micro/nano-structures. After this substrate was immersed into a solution of 1-dodecanethiol, it exhibited superhydrophobic and low adhesion properties with a high contact angle (up to 167°) and a very low sliding angle (<2°) (Zn/Ag superhydrophobic surface). This inexpensive and facile process provides a feasible approach to the large-scale production of superhydrophobic surfaces. To better investigate the potential applications for this superhydrophobic surface, a series of surface-enhanced Raman scattering (SERS) spectra were collected as the volume of a drop that was supported on the surface of the substrate decreased. The SERS signal of the molecules in the drop changed regularly, first increasing and then decreasing in intensity, and we achieved the strongest SERS signal using this procedure, which can be utilized to improve the detection limit to a certain degree. This substrate has great potential for applications in highly sensitive SERS assays. [ABSTRACT FROM AUTHOR]

[Display omitted] • A uniform and small-sized (ca. 10 nm) core–shell Ag/o-GQDs nanohybrid are successfully prepared. • The Ag/o-GQDs show unique structure with parallel-interlaced staking of o-GQDs. • The Ag/o-GQDs exhibit excellent SERS sensitivity, biocompatibility and nanozymatic activity. • The intracellular H 2 O 2 can be accurately in situ SERS monitoring at the subcellular level. The small-sized plasmonic nanoparticles are easily internalized by cells and organelles, but usually possess poor surface-enhanced Raman scattering (SERS) activity, restricting their promising applications for intracellular SERS analysis. To break the current bottleneck of intracellular SERS application, herein, a uniform and small-sized (ca. 10 nm) core–shell Ag/oxidized graphene quantum dots (o-GQDs) nanohybrids have been prepared. The Ag/o-GQDs inherit unique features with parallel-interlaced stacking of o-GQDs as capping agent, possess the increasing and broadening plasmon adsorption and display a unique edge state charge transfer (CT) resonance in the long-wavelength region of visible light, enabling the enhanced electromagnetic (EM) and CT effect for superior SERS sensitivity at lower energy. Further, the Ag/o-GQDs demonstrate excellent biocompatibility and highly efficient nanozymatically catalytic activity, which are first put forward to integrate efficient SERS with Ag/o-GQDs nanozyme to catalyze peroxidase-like reaction for accurate sensing of the intracellular H 2 O 2 at the subcellular level. Moreover, the Ag/o-GQDs nanozyme-catalyzed reactive oxygen species (ROS) generation and the cancer cell multisubcellular-targeting capability provide a promising strategy for the synergistically catalytic therapy specifically toward tumors. This study illustrates a significant route to design an efficient small-sized noble metal/carbon nanozymatic SERS substrate, and demonstrates an exciting potential for ultrasensitive SERS bioanalysis at the subcellular level. [ABSTRACT FROM AUTHOR]

• The first time using the acriflavine molecule as a probe for SERS detection. • The vibrational spectrum of acriflavine was assigned by using DFT calculations. • The detection concentration of Hg2+ by this method is low as 4.7 nmol/L. • The advantages also include low cost, speed, ultra-sensitivity. We conducted a related study on the determination of Hg2+ in water by surface-enhanced Raman scattering (SERS). It is based on acriflavine as a signal probe with the assistance of aggregation agent MgSO 4 for the SERS investigation. Moreover, the density functional theory (DFT) calculations of acriflavine were performed for interpreting the assignments of the vibrational normal modes. The interaction of acriflavine with AgNPs was inhibited because the citrate reduced Hg2+ to Hg and formed Ag amalgam on the AgNPs surface. The formation of Ag-Hg alloys reduced the SERS intensity of acriflavine. This sensing system displayed excellent sensitivity and a detection limit as low as 1.4 mol L −1. The relationship between the SERS intensity and Hg2+ concentration was found in the range of 0.1–8.0 × 10−7 mol L −1. This method for detecting Hg2+ is inexpensive, facile and sensitive. [ABSTRACT FROM AUTHOR]

Protein S-nitrosylation is an important post-translational modification, which has important effect on protein functions and is relevant to various diseases. For quantification of the S-nitrosated proteins, it is still challenging to establish a detection method in combination of fast and one-step determination, highly sensitivity and accuracy. Here, we develop a label-free, direct detection method for S-nitrosated proteins based on resonance Raman scattering of ferrous cytochrome c. The laser source of the Raman spectrometer is utilized both for inducing NO leakage and for Raman scattering excitation. The heme ligation alteration and oxidation enable fast quantification of the released NO by the resonance Raman spectroscopy of the cytochrome c. All the results shown in this study demonstrate the great potential of the proposed method for fast, sensitive and reliable assessment of total S-nitrosated proteins in the clinical applications. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) on organic–inorganic hybrid perovskites have been proved a promising SERS-active substrate. As its inorganic skeleton, lead iodide (PbI 2) also represents a novel semiconductor substrate material that serves as either a complement or an alternative to conventional metal-based SERS. Here, for the first time, enhanced Raman scattering (ERS) of 1,2-bis(4-pyridyl)ethylene (BPE) adsorbed on PbI 2 film is observed. To our surprise, we obtained the same ERS spectra on the PbI 2 as SERS spectra obtained on the perovskites, which demonstrates the enhancement of substrate comes from inorganic skeleton rather than organic–inorganic hybrid perovskites. Compared with the normal Raman spectrum of BPE molecules, we find the B u mode of the BPE molecule was selectively enhanced. We demonstrate that it involves a charge transfer (CT) resonance mechanism and takes place between the HOMO of BPE and the conduction band edge of PbI 2. Moreover, the PbI 2 substrate performs good reproducibility, uniformity and good Raman enhancement (EF ≥ 105). It is believed that this unusual discovery not only enables PbI 2 to be an enhanced substrate, which also provides a new advance toward a better understanding of SERS chemical mechanism. Unlabelled Image • We demonstrate inorganic skeleton as the substrate. • A molecule-to-semiconductor charge transfer mechanism is proposed. • The PbI 2 exibited good reproducibility, uniformity and good enhancement (EF≥105) [ABSTRACT FROM AUTHOR]