Synthesis, And Self-assembly Of PSMA@Ag Core-shell Microspheres And Their Effect On Surface Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) spectroscopy has been intensely explored as a powerful and extremely sensitive analytical technique with vast potential applications in biological, chemical, and environmental monitoring, for its integration of high sensitivity, strong anti-interference ability and non-destructive data acquisition. The appropriate substrate is the premise to obtain favorable signals of surface-enhanced Raman scattering. So, the study of SERS-active substrates is an important research topic. Now, the well studied gold and silver electrodes or colloidal suspensions generally result in irreproducible SERS signals due to the random distribution of hot spots. Then, noble metal ordered nanoarrays have been developed as SERS-active substrates to yield uniform and reproducible SERS signals. Nevertheless, the fabrication of those substrates generally requires relatively complicated manipulations and expensive costs, which limit their wide applications. To solve these problems, the poly(styrene-co-maleic anhydride)@Ag (PSMA@Ag) core-shell microspheres were prepared by the in situ reduction method. Then, the PSMA@Ag photonic crystal films were prepared by self-assembling the PSMA@Ag core-shell microspheres. The PSMA@Ag opal photonic crystal films, as SERS substrates, exhibited high SERS enhancement ability.In this paper, the PSMA@Ag core-shell microspheres were prepared by the in situ reduction method. In the first step, monodispersed PSMA colloids as core particles were prepared by emulsion polymerization and then modified with polyethyleneimine (PEI). Subsequently, Ag seeds were formed in situ and immobilized on the surface of PSMA colloids by adding AgNO3 solution into the PEI modified PSMA colloids. Finally, ethylenediamine tetraacetic acid tetrasodium salt (Na4EDTA) was added in the dispersion to promote the Ag seeds growth and increase thickness of the Ag shell. The experimental parameters, such as the reaction temperature, the concentration of AgNO3 solution, and the concentration of Na4EDTA solution were optimized for improvement of Ag coat coverage. Ultimately, the optimum parameters were obtained through a series of experiments, and well dispersed, uniformly coated PSMA@Ag core-shell microspheres with three different sizes were successfully fabricated. The PSMA@Ag opal photonic crystal films were prepared by self-assembly of PSMA@Ag core-shell microspheres with high zeta potential via the vertical deposition process. Due to the existence of photonic band gap in visible light region, PSMA@Ag photonic crystal films were capable of generating structure colour.The PSMA@Ag photonic crystal films, as SERS substrate, exhibited high SERS enhancement ability. The number of Ag nanoparticles and position of photonic band gap of the substrate have impacts on SERS effect. As the number of Ag nanoparticles increases, the number of hot spots will certainly also increase, and the larger SERS intensity will be obtained. When the wavelength of laser locates in the position of the edge of photonic band gap where has large density of optical state, the interaction between laser and the matter will be enhanced and that leads to an increase in SERS enhancement.The SERS properties of PSMA@Ag photonic crystal films were studied using the p-aminothiophenol (PATP) as detective molecule. The detection limit of 10-8 M for PATP was achieved. The relative deviation of the band intensity of 5 random spots on the substrate is 15%. The attenuation amplitude of the characteristic band intensity was not abivious over 30 days. The substrate exhibits high sensibility, good uniformity and stability. In conclusion, the superior SERS substrate, which has important potential applications in biological, chemical, and environmental analysis and detection, has been prepared in a simple and cheap method.