•The interaction between 4-thiothymidine and human serum albumin was investigated.•S4TdR has moderate affinities for HSA and binds mainly to subdomain IIA.•The quenching mechanism of the S4TdR–HSA complexation is a static quenching.•The morphology and aggregation of the interaction were shown by AFM.•The hydrophobic plays an important role in the interaction between S4TdR and HSA.The interaction of 4-thiothymidine (S4TdR) with human serum albumin (HSA) was studied by equilibrium dialysis under normal physiological conditions. In this work, the mechanism of the interaction between S4TdR and human serum albumin (HSA) was exploited by fluorescence, UV, CD circular, and SERS spectroscopic. Fluorescence and UV spectroscopy suggest that HSA intensities are significantly decreased when adding S4TdR to HAS, and the quenching mechanism of the fluorescence is static. Also, the ΔG, ΔH, and ΔS values across temperature indicated that hydrophobic interaction was the predominant binding force. The CD circular results show that there is little change in the secondary structure of HSA except the environment of amino acid changes when adding S4TdR to HSA. The surface-enhanced Raman scattering (SERS) shows that the interaction between S4TdR and HSA can be achieved through different binding sites which are probably located in the II A and III A hydrophobic pockets of HSA which correspond to Sudlow’s I and II binding sites. In addition, the molecular modeling displays that S4TdR–HSA complex is stabilized by hydrophobic forces, which result from amino acid residues. The atomic force microscopy results revealed that the single HSA molecular dimensions were larger after interaction of 4-thiothymidine. This work would be useful to understand the state of the transportation, distribution, and metabolism of the anticancer drugs in the human body, and it could provide a useful biochemistry parameter for the development of new anti-cancer drugs and research of pharmacology mechanisms.The S4TdR–HSA was evaluated by molecular modeling. Their activity and interaction were displayed in modeling calculations.

•The intermolecular hydrogen bonds of MH in solid state were investigated.•SERS spectra of MH recorded using gold colloidal nanoparticles were studied.•The effect of concentration and pH on the SERS spectra of MH was discussed.•UV spectra of gold colloid with MH in varied pH were analyzed.•The detection limit of the MH solution can be as low as ∼1 ppm.In this paper, surface-enhanced Raman scattering (SERS) spectra of maleic hydrazide (MH, 6-hydroxy-3(2H)-pyridazinone) were studied by using citrate-reduced gold colloidal nanoparticles. Comparisons between the prominent SERS bands and the precise mode descriptions predicted through density functional theory (DFT) simulations at the B3LYP/6-311++g(d,p) level allowed an in-depth orientation analysis of the adsorbed species on gold surfaces. And main forms of hydrogen bonds in the solid state of MH were also determined to be OH⋯O. Furthermore, the effects of concentration and pH on the SERS spectra of the molecule were discussed. It is found that with the different adsorbate concentration, the SERS spectra of MH show significant changes in their features, indicating different orientations and adsorption sites of the molecule on the gold colloidal surface. The SERS and absorption spectra under different pH conditions show that a basic environment leads to the deprotonation of N2 and the nearly parallel orientation of the MH molecule on the gold surface. Moreover, the enhanced characteristic bands were observed at MH concentrations down to about 1 ppm with the gold colloids, demonstrating a potential of the technique in the analysis of MH residues.Graphical abstract

The paper investigated the residual ions in hydroxylamine-reduced silver colloid (HRSC) and the relationship between the condition of HRSC and the enhanced mechanisms of this colloid. We also detected the SERS of MB and studied the effects of anions on the Raman signal. In the case of HRSC, the bands of residual ions diminish while the bands of Ag-anions increase gradually with increasing the concentrations of Cl− and NO3−. It means the affinity of residual ions on the silver surface is weaker than that of Cl− and NO3− and the residual ions are replaced gradually by the added Cl− or NO3−. The Raman signal of residual ions can be detected by treatment with anions that do not bind strongly to the silver surface, such as SO42−. The most intense band of Ag-anions bonds can be also observed when adding weakly binding anions to the colloid. However, the anions which make up the Ag-anions bonds are residual Cl− and the effect of weakly binding anions is only to aggregate the silver particles. Residual Cl− can be replaced by I− which has the highest affinity. From the detection of methylene blue (MB), the effects of anions on the enhancement of Raman signal are discussed in detail, and these findings could make the conditions suitable for detecting analytes in high efficiency. This study will have a profound implication to SERS users about their interpretation of SERS spectra when obtaining these anomalous bands.Graphical abstractHighlights► The paper studied the SERS of HRSC when adding a great range of anions. ► The SERS of residual impurities in HRSC was further investigated. ► The relationship between the condition of HRSC and the enhancement was studied. ► We detected the SERS of MB and studied the effects of anions on the Raman signal. ► This study makes the conditions suitable for detecting analytes in high efficiency.

The influences of concentration, halide anions and pH on the surface-enhanced Raman scattering (SERS) of riboflavin adsorbed on borohydride-reduced silver colloids were studied. The optimum concentration for the SERS of riboflavin is 10−6 mol/L while the SERS enhancement varies for different modes. The addition of 0.2 mol/L halide (NaCl, NaBr, and NaI) aqueous solutions, leads to a general decrease of the SERS intensity and a change of spectral profile of riboflavin excited at 514.5 nm. Riboflavin interacts with the silver surface possibly through the CO and N–H modes of the uracil ring. The SERS spectra of riboflavin were recorded in the 3.4–11.6 pH range. By analyzing several SERS marker bands, the protonated, deprotonated or the coexistence of both molecular species adsorbed on the colloidal silver particles was proved.Graphical abstractHighlights► New adsorption geometries of riboflavin molecules on silver surface were verified. ► The optimum concentration for the SERS of riboflavin was found at 10−6 mol/L. ► The addition of 0.2 mol/L halide leads to the changes of SERS intensity and profile. ► The protonated and deprotonated molecular species of riboflavin adsorbed were proved.

In this report, Raman and surface-enhanced Raman scattering (SERS) spectra of captopril are studied in detail. Herein, the Raman bands are assigned by the density functional theory (DFT) calculations and potential energy distributions (PED) based on internal coordinates of the molecule, which are found to be in good agree with the experimental values. Furthermore, the concentration and pH dependence of the SERS intensity of the molecule is discussed. By analyzing the intensities variation of SERS bands of the different concentrations of captopril solution, it can be concluded that the molecules orientation adsorbed on the silver nanoparticles surface change with the change of the concentrations. The variation of SERS spectra of captopril with the change of pH suggests that the interaction among the adsorbates with Ag cluster depend on the protonated state of the adsorbate and the aggregation of silver nanoparticles.Highlights► The captopril was assigned by the assistance of PED and DFT. ► The adsorption behavior of captopril on silver surface was studied. ► Concentration and pH-dependent SERS spectra of captopril molecule adsorbed on nano-colloidal silver surface were studied.

First of all the surface enhanced Raman spectroscopy (SERS) and normal Raman spectra of caffeine aqueous solution were obtained at different pH values. In order to obtain the detailed vibrational assignments of the Raman spectroscopy, the geometry of caffeine molecule was optimized by density functional theory (DFT) calculation. By comparing the SERS of caffeine with its normal spectra at different pH values; it is concluded that pH value can dramatically affect the SERS of caffeine, but barely affect the normal Raman spectrum of caffeine aqueous solution. It can essentially affect the reorientation of caffeine molecule to the Ag colloid surface, but cannot impact the vibration of functional groups and chemical bonds in caffeine molecule.

The surface enhanced Raman scattering (SERS) of caffeine on borohydride-reduced silver colloids system under different aqueous solution environment has been studied in this paper. The relative intensity of SERS of caffeine significantly varies with different concentrations of sodium chloride and silver particles. However, at too high or too low concentration of sodium chloride and silver particle, the enhancement of SERS spectra is not evident. The SERS spectra of caffeine suggest that the contribution of the charge transfer mechanism to SERS may be dominant. The chloride ions can significantly enhance the efficiency of SERS, while the enhancement is selective, as the efficiency in charge transfer enhancement is higher than in electromagnetic enhancement. Therefore, it can be concluded that the active site of chloride ion locates on the bond between the caffeine and the silver surface. In addition, the SERS spectra of caffeine on borohydride-reduced and citrate-reduced silver colloids are different, which may be due to different states caffeine adsorbed on silver surface under different silver colloids.

Raman and SERS spectra of homodipeptide Gly-Gly and Gly were recorded and compared in this paper, and band assignment for the functional groups contained in these molecules was analyzed in detail. Time-dependent and pH-dependent SERS spectra of Gly-Gly molecule adsorbed on nano-colloidal silver surface were also studied. The time-dependent SERS spectra of Gly-Gly are characterized by the increase in intensity of bands primarily representing the vibrational signatures emanating from the amino and amide moiety of Gly-Gly molecule. It is found that the adsorption style of Gly-Gly on the silver colloid changes as time goes on; at 5 min after adding the sample to the silver colloid, Gly-Gly adsorbs on silver surface firstly through the carboxylate, amino and amide groups, and then the carboxylate group is far away from the silver surface at 10 min to 3 days. The SERS variation of Gly-Gly with the change of pH suggests that the adsorption style is pH-dependent, the different adsorption behavior of the Gly-Gly occurs on silver surface at different pH values.

The paper further investigated the relationship between the modification of the surface chemistry and the enhancement mechanisms of borohydride-reduced silver particles (BRSC). The bands of residual ions die down while the anomalous bands increase gradually with the increasing of the concentration of Cl− and Br−. It means the residual ions are displaced gradually by the added Cl− or Br− and the two halides can lead to the aggregation of the BRSC to a certain extent. However, the most strongly binding anions – I−, cannot cause any aggregation of silver particles. From the detection of methylene blue (MB), the relationship between the modification of silver surface chemistry and the enhancement mechanisms was discussed. Chloride gives the greatest enhancement while the iodide gives the lowest enhancement among the different kinds of anions. There are also some anomalous bands in the SERS spectra of MB, and these anomalous bands were given rational explanation in this paper.

The surface enhanced Raman scattering (SERS) spectrum of methylene blue (MB) varies observably when using different kinds of silver colloids as SERS active substrates. The colloids were synthesized by three different methods. Sodium chloride, sodium sulfate, sodium nitrate were chosen as aggregating agents in this study. Three kinds of anions were performed on hydroxylamine-reduced silver colloid and the effect of the chloride anion was investigated in the three SERS-active colloids. From the results it can be concluded that the interaction between analyte and silver nanoparticles is different in different kinds of colloidal environments and the addition of anions also has a great influence on SERS spectrum. The effects on the SERS spectra were qualitatively explained through the study of SERS spectra for various silver colloids and aggregating agents in this paper.