The authors have developed a surface-enhanced Raman spectroscopic (SERS) method for the determination of pyrophosphate ion (PPi). It is based on the competitive coordination of Cu(II) between cysteine (Cys) and PPi using silver nanoparticles (AgNPs) modified with Cys and Rhodamine 6G (R6G). Cys was attached to the surface of the AgNPs via Ag−S bond, and the amino acid unit in Cys bind to Cu(II) to form a chelate complex. This results in the aggregation of AgNPs and a strong SERS signal for the probe R6G. However, in the presence of PPi, the aggregated AgNPs are solubilized because of the stronger affinity between PPi and Cu(II). This leads to a decrease of the SERS signal and forms the basis for the quantitation of PPi. The amount of AgNPs, the concentration of Cu(II), and the mixing time were optimized. The method displays a linear response in the 0.1 to 80 μM PPi concentration range, and the limit of detection is as low as 20 nM. The method was applied to the determination of PPi in spiked serum samples and urine samples, with recoveries between 95.2 to 100.5% and relative standard deviations of <4.4%.

•The silver nanoparticles-coated silicon wafer (AgNPs@Si) was served as SERS substrate for the detection of 6-Thioguanine (6-TG).•With the 521 cm−1 band of silicon as internal standard, band intensity ratio of 6-TG to silicon, that is I1303/I521, can be used for quantification.•Figures of merit were evaluated (linear range, sensitivity, selectivity, recovery).•The detection limit (S/N = 3) is 0.065 μmol L−1.In this paper, silver nanoparticles-coated silicon wafer (AgNPs@Si) was used as surface-enhanced Raman scattering (SERS) substrate for detection of 6-Thioguanine (6-TG). The influence of experimental parameters including pH value and soaking time on SERS performance were examined. The SERS characteristic peak of 6-TG at 1303 cm−1 was selected for quantity analysis. With the 521 cm−1 band of silicon as internal standard, band intensity ratio of 6-TG to silicon, that was I1303/I521, could be used for quantification. Under the optimum conditions, I1303/I521 exhibited a linear relationship with the concentration of 6-TG in the range of 0.1–15.0 μmol L−1 and detection limit (S/N = 3) was 0.065 μmol L−1. The corresponding correlation coefficient of the linear equation was 0.998. This method based on AgNPs@Si was successfully applied to the detection of 6-TG in two kinds of commercial tablets.

•The silver nanowires-coated silicon wafer (AgNWs-Si) was served as SERS substrate for detecting 6-Mercaptopurine (6-MP).•The prepared AgNWs were characterized by TEM image, UV–vis spectroscopy and X-ray diffraction.•With the 521 cm−1 band of silicon as internal standard, band intensity ratio of 6-MP to silicon, that is I1001/I521, can be used for quantification.•The detection limit (S/N = 3) is 0.012 μmol L−1 and the linear concentration range is 0.05–3.8 μmol L−1.The silver nanowires (AgNWs) were prepared through the method of polyol. The prepared AgNWs were characterized by TEM image, UV–vis spectroscopy and X-ray diffraction (XRD). AgNWs were assembled onto silicon wafer through entropy-driven self-assembly method. The 521 cm−1 band of silicon was used as internal standard band. The SERS performance of AgNWs-Si substrate was characterized by using R6G as the probe molecule, and the SERS substrate is employed to detect 6-MP. The linear concentration range of 6-MP is 0.05–3.8 μmolL−1 and the corresponding correlation coefficient is 0.994. The method is satisfactory for detecting 6-MP in two kinds of commercial tablets.

Although classical silver nanospheres were widely used as probes in surface-enhanced Raman spectroscopy (SERS), they lacked long-term stability. In the present work, silver nanoparticles decorated with β-cyclodextrin (β-CD–AgNPs) were used as probes and the stability was improved. The adsorption characteristics of 6-mercaptopurine (6-MP) on classical silver nanospheres and β-CD–AgNPs were studied cautiously using SERS, and chemical information about the molecular structure was obtained. The binding of the 6-MP molecule to the surface of AgNPs is based on the stable Ag–S covalent bond. The electrostatic adsorption between the protonated N7 atom or N1 atom and the silver surface results in a notable Raman enhancement. The intensity of the Raman band of 6-MP at 866 cm−1 was used to determine 6-MP. Experimental conditions, such as the volume of CD–AgNP solution, incubation time, pH value and concentration of sodium chloride, were examined and optimized. Compared with classical silver nanospheres, when β-CD–Ag nanoparticles were used, the sensitivity was higher, the analytical time was shorter, and the linear range was wider. A good linearity (r = 0.996) in the range of (0.040–2.0) × 10−7 mol L−1 was obtained for determining 6-MP. The limit of detection was 0.024 × 10−7 mol L−1 and the limit of quantification was 0.080 × 10−7 mol L−1. This method was successfully applied to the determination of 6-MP in real samples and the results were satisfactory.

•Methimazole was determined based on LSPR using gold nanoparticles as the probe.•SERS gives chemical information of methimazole on the molecular structure.•The proposed method is simple and sensitive.•The sensitivity of Au–Ag–Au double shell was higher than gold nanospheres.In this paper, Au–Ag–Au double shell nanoparticles were prepared based on the reduction of the metal salts HAuCl4 and AgNO3 at the surface of seed particles. Due to the synergistic effect between Au and Ag, the hybrid nanoparticles are particularly stable and show excellent performances on the detection of 2-mercapto-1-methylimidazole (methimazole). The binding of target molecule at the surface of Au–Ag–Au double shell nanoparticles was demonstrated based on both localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS) spectra. The LSPR intensity is directly proportional to the methimazole concentration in the range of 0.10–3.00×10−7 mol L−1. The SERS spectrum can be applied in identification of methimazole molecule. The LSPR coupled with SERS based on the Au–Ag–Au double shell nanoparticles would be very attractive for the quantitative determination and qualitative analysis of the analytes in medicines.

The noble metal nanoparticles (NPs), including gold nanorods (AuNRs), gold nanospheres (AuNSs) and silver nanoplates (AgNPTs), were synthesized and Tween 20 stabilized NPs (Tween 20-NPs) were used as the probes for determining Hg2+. Hg2+ was determined based on the strong affinity between Au (Ag) and Hg. Hg2+ was reduced to Hg in the presence of sodium borohydride. Hg interacts with the NPs and the diameter of the NPs decreases with the increase of Hg2+ concentration, which causes the shift in absorption peak of Tween 20-NPs. The peak shifts are linearly related to Hg2+ concentrations. Compared with AuNSs and AgNPTs, when the AuNRs was used, the sensitivity for determining Hg2+ was higher. The developed method shows a good selectivity for Hg2+ and can be applied to the determination of Hg2+ in water samples.Graphical abstractThe noble metal nanoparticles (NPs), including gold nanorods (AuNRs), gold nanospheres (AuNSs) and silver nanoplates (AgNPTs), were synthesized. Hg2+ was determined using these NPs as probes. The sensitivity for determining Hg2+ obtained with AuNRs was the highest.Highlights► The sensitivity for determining mercury(II) ion using different shape nanoparticles as the probes was investigated. ► The proposed method is simple and sensitive. ► Compared with gold nanospheres and silver nanoplates, the gold nanorods have higher sensitivity for determining Hg2+.

Silver nanoparticles (Ag NPs) modified with sodium 2-mercaptoethanesulfonate (mesna) exhibit strong surface-enhanced Raman scattering (SERS). Their specific and strong interaction with heavy metal ions led to a label-free assay for Hg(II). The covalent bond formed between mercury and sulfur is stronger than the one between silver and sulfur and thus prevents the adsorption of mesna on the surface of Ag NPs. This results in a decrease of the intensity of SERS in the presence of Hg(II) ions. The Raman peak at 795 cm−1 can be used for quantification. The effect of the concentration of mesna, the concentration of sodium chloride, incubation time and pH value on SERS were optimized. Under the optimal conditions, the intensity of SERS decreases with increasing concentration of Hg(II). The decrease is linear in the 0.01 and 2 μmol L−1 concentration range, with a correlation coefficient (R2) of 0.996 and detection limit (S/N = 3) is 0.0024 μmol L−1. The method was successfully applied to the determination of the Hg(II) in spiked water samples.

We report on a novel biosensor for determining sequence-specific DNA. It is based on resonance light scattering (RLS) caused by the aggregation of gold bipyramids. These display localized surface plasmon resonance and can be used as a bioprobe. The absorption spectra and the transmission electron micrographs provide visual evidence of the aggregation of the gold bipyramids in the presence of DNA. The RLS intensity of the gold bipyramids increases with the concentration of the target DNA. The method was successfully applied to the determination of a 30-mer single-stranded oligonucleotide and works over the 0.1–10 nM concentration range.

Based on the surface-enhanced Raman scattering (SERS) sodium 2-mercaptoethanesulfonate (mesna) was determined using unmodified gold colloid as the probe. The Raman scattering intensity was obviously enhanced in the presence of sodium chloride. The influence of experimental parameters, such as incubation time, sodium chloride concentration and pH value on SERS performance was examined. Under the optimum conditions, the SERS intensity is proportional to the concentration of mesna in the range of 9.0 × 10−8 to 9.0 × 10−7 mol/L and detection limit (S/N = 3) is 1.16 × 10−8 mol/L. The corresponding correlation coefficient of the linear equation is 0.996, which indicates that there is a good linear relationship between SERS intensity and mesna concentration. The experimental results indicate that the proposed method is a viable method for determination of mesna. The real samples were analyzed and the results obtained were satisfactory.Graphical abstractThe aggregated gold colloids caused by the addition of NaCl shows high SERS activity, thus it is used for the sodium 2-mercaptoethanesulfonate determination.Highlights► A quantitative measure of the sodium 2-mercaptoethanesulfonate by SERS is obtained. ► The sodium chloride was added into the gold colloids to obtain the reproducible spectra. ► The method is sensitive, simple, and rapid.

Although classical silver nanospheres were widely used as probes in surface-enhanced Raman spectroscopy (SERS), they lacked long-term stability. In the present work, silver nanoparticles decorated with β-cyclodextrin (β-CD–AgNPs) were used as probes and the stability was improved. The adsorption characteristics of 6-mercaptopurine (6-MP) on classical silver nanospheres and β-CD–AgNPs were studied cautiously using SERS, and chemical information about the molecular structure was obtained. The binding of the 6-MP molecule to the surface of AgNPs is based on the stable Ag–S covalent bond. The electrostatic adsorption between the protonated N7 atom or N1 atom and the silver surface results in a notable Raman enhancement. The intensity of the Raman band of 6-MP at 866 cm−1 was used to determine 6-MP. Experimental conditions, such as the volume of CD–AgNP solution, incubation time, pH value and concentration of sodium chloride, were examined and optimized. Compared with classical silver nanospheres, when β-CD–Ag nanoparticles were used, the sensitivity was higher, the analytical time was shorter, and the linear range was wider. A good linearity (r = 0.996) in the range of (0.040–2.0) × 10−7 mol L−1 was obtained for determining 6-MP. The limit of detection was 0.024 × 10−7 mol L−1 and the limit of quantification was 0.080 × 10−7 mol L−1. This method was successfully applied to the determination of 6-MP in real samples and the results were satisfactory.