AgNFs supported on graphene based materials as multi-wavelength SERS active platforms

Surface Enhanced Raman Spectroscopy (SERS) has been successfully employed in several fields of interest such as plasmonic sensing and biosensing, in-situ photocatalysis studies, single molecule detection, environmental and many others real-world applications. To further potentiate the SERS effect, several research studies reported the employ of peculiar plasmonic nanostructures characterized by intense electromagnetic hot-spots. Moreover, the possibility to amplify Raman signals is strongly linked to the excitation wavelength of the laser interacting with the SER active substrate. In order to explore novel functional nanomaterials with high enhancement in a wide range of excitation wavelengths, we propose Silver Nanoflowers (AgNFs), anchorated to graphene oxide (GO), reduced (rGO) and thiolated (GOSH) graphene oxide layers. The success of the metal-graphene coupling procedure was verified by UV-visible and Raman spectroscopy. A morphological characterization of the new materials was carried out by using scanning electron and atomic force microscopies. Thanks to the NFs morphology and the large surface of the hybrid platforms, it was possible to create a numberless of hot spot regions between silver petals and in the nanogaps at the AgNFs/GO, rGO, GOSH interface. SERS properties of the hybrid materials were studied using a standard molecule 4-mercaptobenzoic acid (4-MBA) as probe analyte at the nanomolar concentration. As the AgNFs extinction spectra cover the entire visible range, we were able to study the enhancement in a laser wavelength range between 532 and 785 nm, finding very high enhancement factors. This suggests that AgNF-Graphene based materials could be an excellent SERS substrate on the entire visible and near infrared spectral region, opening the possibility to investigate several biological and medical interest analytes without the interference of not desired optical phenomena such as luminescence.