A Research On SERS Spectroscopy Of Redox Reaction On Gold Nanoparticles And Its Application

In this paper,the REDOX reaction mechanism and the applications on Au NPs were studied by employing gold nanoparticles(Au NPs)as the Surface Enhanced Raman Scattering(SERS)substrate.Using p-nitrothiophenol(PNTP),p-aminodiphenyl disulfide(APDS)and p-mercaptophenylacetylene(PMPA)as probe molecules,respectively,the PNTP-Au NPs system was constructed in solid phase condition and the PNTP-Au NPs system,APDS-Au NPs system and PMPA-Au NPs system were constructed in liquid phase condition.These systems were used to investage the reaction mechanism and applications of SERS.(1)In solid phase condition,the SO₃^2-was introduced to the system of PNTP-Au NPs to realize the conversion of PNTP to p,p'-dimercaptoazobenzene(DMAB)on Au NPs.By contrast tests,the conversion of PNTP to DMAB in PNTP-Au NPs system was determined to be the result of the interaction of both Au NPs and SO₃^2-.In order to verify this result,the exposure time was increased to the PNTP-Au NPs system and other external anions,such as HSO₄^-,SO₄^2-,Br^-,and Cl^-,were added to the PNTP-Au NPs system.But none could induce the same effect.On the basis of this experimental result,the mechanism of the conversion of PNTP to DMAB on Au NPs induced by SO₃^2-was discussed.Under the laser irradiation,a huge number of“holes”and“electrons”were generated on the surface of Au NPs.The“holes”were combined by SO₃^2-,resulting in a large number of isolated reductive“electrons”to reduce the PNTP to DMAB.(2)In liquid phase condition,the Fe²⁺was employed as a reductant to the PNTP-Au NPs system to reduce the PNTP to DMAB.Other cations,such as Ca²⁺,Au³⁺,Co²⁺,and Mg²⁺,were added to the solution of PNTP-Au NPs to contrast whether the same transition would be appeared.The experimental result showed that the PNTP-Au NPs was highly selective to Fe²⁺in liquid phase condition.When the range of Fe²⁺concentration was from 10 to 100?M,the conversion of DMAB was changed regularly as the concentration of Fe²⁺changed.To verify the new technique in determinating Fe²⁺,actual samples were tested by spike-and-recovery experience.The determination results showed that the relative standard deviations(RSD)were all less than 5%,and the recoveries were all greater than 80%.When the concentration of Fe²⁺was below 10?M,the result revealed the minimum detectable concentration of Fe²⁺was as low as 1?M in the PNTP-Au NPs system under liquid phase.(3)The APDS-Au NPs system was uesd to determinate Ag⁺.Under alkaline condition,several cations,such as Ag⁺,Au³⁺,Co²⁺,and Mg²⁺,were added to the solution of APDS-Au NPs,the result indicated that both Au³⁺and Ag⁺could trigger the conversion of APDS to DMAB.This problem could be solved by adjusting the p H value.In acid condition,the separation of Au³⁺and Ag⁺was achieved.When the concentration of Ag⁺was in the range of 10?100?M,with the increasing of Ag⁺concentration,the transition of APDS to DMAB was increasing gradually.A good linear relationship was obtained and the limit of detection was 7?M.To verify the new technique in determinating Ag⁺,actual samples were tested by spike-and-recovery experience.The determination results showed that the RSD were all less than 5%,and the recoveries were all greater than 90%.(4)The oxidation reaction of PMPA on Au NPs was investigated with SERS technique.The PMPA could be oxidized to p-mercaptoacetophenone(PMAP)under irradiation of laser after adjusting the reaction environment to alkaline by using morpholine.We optimized the reaction conditions in subsequent study,when the mass of morpholine added was 50?g,the conversion rate of PMAP was the highest.Simultaneously,other bases were used to adjust the reaction condition,but none of the bases could induce the same phenomenon.This experimental result showed that it is possible to use SERS technique to replace the complex and tedious reaction conditions in the traditional organic synthesis with the advantages of more efficiency and safety.