AgNFs as single-particle, multi-wavelength SERS active platforms

Surface Enhanced Raman Spectroscopy (SERS) has been successfully employed in several fields of interest such as biosensing, in-situ catalysis studies, and archeology. Usually, the greatest contribution to the Raman enhancement is explained by an electromagnetic mechanism [1]. To amplify the SERS effect, the research studies report the production of nanostructures that allow the creation of hot-spots on the surface [2]. Furthermore, the possibility of amplifying Raman signals is linked to the excitation wavelength of the laser used [3]. In this work, we present a SERS active substrate with a high enhancement in a wide range of excitation wavelengths. We propose Silver Nanoflowers (AgNFs), metal microparticles with a nanorough surface that creates a pattern of petals. Thanks to their dimension is possible, by using a Micro-Raman spectrometer, to quickly find a single microparticle and study the signal enhancement of an analyte adsorbed onto its surface. The SERS properties at a single-particle level were studied using a standard molecule 4-mercaptobenzoic acid (4-MBA). As the AgNFs extinction spectra cover the entire visible range, we were able to study the enhancement for the single AgNF with 532, 633, and 785 nm laser wavelengths, finding very high enhancement factors, due to several number of hot-spots on the tips and between the petals. This suggests that the AgNF could be an excellent SERS substrate on the entire visible and near infrared spectral region and demonstrates that such nanomaterial can be easily used to study analytes at low concentrations with any exciting wavelength, opening the possibility to study several biological and medical interest analytes without the interference of not desired optical phenomena such as luminescence.