Detection Of Fluoride And Pyrophosphate Ions In Water Based On SERS Technology

Anions play an important role in various chemical and biological processes.Compared with cations,the detection of anions is more difficult due to their special properties,such as solvation effect,electrostatic attraction,and different shapes.Traditional detection methods,including ion chromatography,mass spectrometry,fluorescence,and colorimetry,have been widely applied for quantitative detection of inorganic ions.However,most of these methods suffer from complicated operation,time-consuming,and expensive instruments.Recently,surface-enhanced Raman scattering?SERS?technology has become a popular detection technology because of its easy operation,high sensitivity,and strong accuracy,which has a great potential for on-site analysis.At present,SERS technology has been achieved excellent results in various fields.This paper applied the SERS technique to the detection of anions in water,mainly focusing on the quantitative determination of fluoride ions and pyrophosphate ions?PPi?in water.The main research contents and innovations are as follows:?1?4-Mercaptophenylboronic Acid?4-MPBA?was selected as the molecular probe for fluoride ions detection.The principle of sensing strategy is based on fluoride-induced structural symmetry breaking and charge redistribution of phenylboronic acid,leading to a band shift of the C-C stretching mode of 4-MPBA from 1589 to 1576 cm^-1.The sensing mechanism has been fully studied by density functional theory?DFT?calculations.Accordingly,a ratiometric signal of the area ratio(A₁₅₇₆/A₁₅₈₉)between the fluoride-bond MPBA molecules and unoccupied MPBA molecules can be used for the quantitative response of F^-ions.The proposed SERS sensor exhibits high selectivity for F^-ions with the determination limit of 10^-8M,which is much lower than the World Health Organization?WHO?guideline value for F^-ions in drinking water.Of particular significance,the present sensor features favorable recyclability,which preserves suitable reproducibility during 6-time cyclic determination of F^-ions.The present silicon-based SERS sensor could serve as a promising sensor for on-site applications.?2?3-amino-5-mercapto-1,2,4-triazole?AMT?molecule was selected as the probe,which can adsorbed on to silicon-based silver SERS substrates?Si@Ag NPs?through the formation of Ag-S bonds.The reaction between Cu²⁺and AMT leads to produce[Cu?Hdatrz?]complexes,which can be observed in SERS spectrum.Upon addition of PPi into the sensing system,the SERS signal will produce a distinct change due the competitive reaction between PPi and[Cu?Hdatrz?]complexes,resulting in the variation of the molecular adsorption orientation on the substrate surface.Quantitative determination of PPi can be achieved by the intensity ratio of 443 cm^-1 and 1398 cm^-1 in the SERS spectrum.The limit of detection can be down to 10 nM,providing the possibility for the PPi detection in water.