Application Of Surface-Enhanced Raman Spectroscopy To Determination Of Pyrophosphate, Safranine T And Hg²⁺

As an ultrasensitive vibrational spectroscopic technique,surface-enhanced Raman spectroscopy?SERS?can provide molecular fingerprint identification and high analytical sensitivity,the advent of SERS has overcome the low sensitivity of traditional Raman spectroscopy.Except for its molecular specificity and high sensitivity,SERS can be applied to water sample analysis and on-site analysis,which makes the sample preparation process easier and saves the analysis time considerably.Because of these advantages,SERS is widely applied in many fields,including environmental analysis,food safety analysis,biomedical analysis and archaeology analysis.In the paper,Pyrophosphate,Safranine T and Mercury were detected by SERS using silver nanoparticles as SERS active substrate.Based on the competitive coordination of Cu?II?between cysteine?Cys?and pyrophosphate ion?PPi?,PPi was detected using silver nanoparticles?Ag NPs?modified with Cys and Rhodamine 6G?R6G?as SERS substrate.Cys was attached to the surface of the Ag NPs 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 Ag NPs and a strong SERS signal for the probe R6 G.However,in the presence of PPi,the aggregated Ag NPs 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 Ag NPs,the concentration of Cu?II?,and the mixing time were optimized.The method displays a linear response in the 0.1 to 80.0 ?M PPi concentration range,and the limit of detection is as low as 20 n M.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 nanospheres were prepared via the classic Lee's method,and they were used as SERS substrates to determine safranine T?ST?and Hg²⁺.ST can absorb on the surface of Ag NPs through electrostatic interaction,the electromagnetic effect combined with chemical adsorption effect give a notable Raman enhancement for ST.The presence of Hg²⁺ well decreased the absorbed ST molecules on Ag NPs,leading to a significantly decrease of SERS signals thus enabled to detect Hg²⁺.The determination conditions for SERS,including the amount of Ag NPs,the concentration of Na Cl,the concentration of HCl,the concentration of ST and the reaction time were optimized.Under the optimized experimental conditions,good linear responses were obtained for ST and Hg²⁺ in the concentration ranges of 0.01–4.0 ?mol L-1 and 0.01– 2.0 ?mol L-1,the limit of detection?LOD?were 3.0 and 2.0 nmol L-1,respectively.The present method was subsequently applied to the determination of ST in tomato sauces and Hg²⁺ in environmental waters,the recoveries of ST and Hg²⁺ in spiked samples are 95.5–107.8 % and 91.4–110.8 %,respectively.