Ag nanoflowers as single-particle, multi-wavelength SERS active platforms

Abstract

Surface-enhanced Raman spectroscopy (SERS) has been successfully employed in several fields of interest such as biosensing, in-situ catalysis studies, and archeology, in this regard, the production of nanostructures for the SERS effect is the core of scientific research. Up to now a lot of different types of metallic nanoparticles and nanosurfaces were produced in trying to match the theoretical enhancement of 1014. This work presents a novel SERS active substrate with a high enhancement and a wide range of exciting wavelengths. Specifically, we synthesize Ag Nanoflowers (AgNFs), spherical silver micro-particles with a diameter of 1.7 μm and a nano-rough surface. When AgNFs are deposited onto a substrate thanks to their dimension is possible, to find a single isolated micro-particle 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). Thanks to their extinction spectrum, expanding throughout the visible range, we were able to systematically study the enhancement for several single Ag NFs with 532, 633, and 785 nm laser wavelengths, finding a maximum enhancement factor in the order of 108- 109. This result is of great interest because demonstrates that such nanomaterial can be easily used to study every kind of analyte at low concentrations with any exciting wavelength thus avoiding other undesired optical phenomena, such as luminescence or degradation of the analyte.