Enhanced Raman Scattering by Polystyrene Microspheres and Application for Detecting Molecules Adsorbed on Au Single Crystal Surface

By assembling polystyrene microspheres on a sample surface, the surface Raman signal could be enhanced. The dependence of the enhancement effect on the size of microspheres was systematically investigated and it was found that microspheres with a diameter of 3.00 μm showed the highest enhancement of ca 5 folds. By utilizing the enhancement effect of the microspheres, the surface Raman intensity of malachite green isothiocyanate (MGITC) adsorbed on Au(111) surface could be enhanced by 20 folds, indicating that this method could effectively improve the detection sensitivity of surface Raman spectroscopy for the adsorbed species on single crystal surface. The later signal increment corresponds to the Raman enhancement effect of nearly 3 orders of magnitude. The enhancement effect is mainly owing to the formation of nanojets when a laser is focused on the microspheres of appropriate diameter. The formation of nanojets will lead to the highly localized electromagnetic field, which will then significantly enhance the Raman process in the nanojets. The main reason for obtaining different enhancements on two types of samples was analyzed.