Investigation of the Factors Influencing the Surface-Enhanced Raman Scattering Activity of Silver Nanoparticles

Abstract

Surface-enhanced Raman scattering (SERS) is one of the most effective methods for applications in optical sensors and chemical analysis. However, control of the optimal conditions of substrates and the selection of chemical probes are two major challenges which have yet to be solved. In this work, using a simple seeded growth method, nanoparticles with different sizes and shapes were produced. The SERS enhancement factor for each nanoparticle size and shape obtained was evaluated based on three different analytes, methylene blue, Nile blue A and Rhodamine B. We found a maximum enhancement factor on the order of 106 for the case of silver nanorods and Rhodamine B. Considering the SERS performance for silver nanospheres, we observed a systematic increase in the sequence methylene blue-Nile blue A-Rhodamine B. The reason behind the enhanced efficiency is that the maximum of the surface plasmon resonance band of Rhodamine B is the closest to the Raman excitation wavelength. The study also demonstrates that a decrease in size of spherical nanoparticles can lead to an increased enhancement, resulting from a larger surface area for a smaller particle size. Compared with silver nanospheres, silver nanorods yielded a better SERS enhancement factor, as a result of shape anisotropy which significantly enhance the local field hotspots. For low concentration, the intensity of Raman bands increases linearly with increasing dye concentration, which could be useful for applications involving chemical sensors.