Investigation On Surface Enhanced Raman Spectroscopy In Different Medium

Surface-enhanced Raman spectroscopy(SERS)has been developed as a powerful tool in the surface science for its ultrahigh surface sensitivity up to the single molecular detection.At present,the well established enhancement mechanisms was mainly included electromagnetic mechanism(EM)and chemical mechanism(CT).In general,the enhancement of EM originated from the surface plasmons resonance(SPR)contributed to SERS dominantly,especially for the "hot spots" effect.So far,there are a lot of experimental and theoretical studies on SERS substrates,involving the fabrication and application.However,the SERS comunity payed much little attention on the influence of medium environments.The main reason is mainly due to the poor uniformity and reproducibility of SERS substrates which brought the lack of comparability of SERS intensities from differnt spots or substrates.Herein,the influence of medium on SERS effect has been explored from the following aspects:1.Exploring the effect of medium environments on SERSat chemical self-assembly substrate.Self-assembled Au and Au@Ag monolayer films were assembled by the interaction between the metal nanoparticles and APTMS functionalized substrates.The large-area SERS mapping and statistical analysis were performed in different medium.The results demonstrated that the improvement of SERS intensities were dependent on the medium environments,laser wavelength and the compact degree in the following sequence H2O>CCl4>air(638 nm),638 nm>532 and 785 nm,and loose>compact.2.Fabricating Au@SiO2 nanoparticles monolayer film(Au@SiO2 MLF)at air/liquid interface for the investigation of medium effect.The SiO2 shell isolated the direct contact between the metal substrate and the medium,resulting in the disappearance of medium effect on SERS intensities.It indicated that the SERS effect of the substrate is only associated with the medium environment around the metal nanoparticles directly.3.Assembling the large area Au and Au@Ag nanoparticles monolayers at gas/liquid interface with high homogeneity fitting for the comparability.Based on the change in the peak intensity of SERS spectra and the SPR catalytic efficiency,the synergetic effect on SERS intensities was explored among medium,laser wavelength and substrate materials effect.The results revealed that the SERS intensity was observed in the sequence of H2O>CC14>air.In H2O medium,the SERS effect and SPR catalytic activity were achieved to maximum on Au and Au@Ag substrates irradiated by 638 and 532 nm laser,respectively.The theoretical consideration of SERS enhancement factor on Au MLF substrates demonstrated that the influences of medium environments allowed the shift of SPR frequency to match the laser for generating the maximum enhancement.It provided an experimental basis for the selection of appropriate substrates,medium and laser wavenegth for the practical applications.