Highly efficient plasmonic nanoplatforms for sensitive surface-enhanced Raman detection of pollutants and peptides

Abstract

The strong intensification of the electromagnetic (EM) field near the surface of metal nanoparticles (NPs) with plasmonic properties results in a substantial enhancement of the effective Raman cross-section leading to SERS (Surface-Enhanced Raman Scattering) effect. An interesting strategy for increasing the sensitivity of metal plasmonic NPs is their assembly by means of bifunctional molecules leading to the formation of interparticle junctions (nanogaps), where a large intensification occurs leading to the creation of hot spots. The performance of these systems could improve by providing these hot spots with a specific molecular functionalization, resulting in a large increase of selectivity. Actually, the formation of hot spots in gaps can be simultaneously induced by the molecular functionalization (Figure 1). In this work we present the results obtained by using aliphatic dithiols to induce the NPs linking and the subsequent formation of nanogaps. These molecules have two different roles: a) NPs linking to create hot spots; and b) the molecular hosting inside the interparticle gaps aimed to detect compounds of interest inside such cavities (Figure 1). Additionally, the SERS spectra were able to provide a rich information about some important aspects regarding the adsorption, coordination and structural changes of the linker on the metal. The structural study conducted in this work also permitted the study of the conformational order and packing of the aliphatic chains of these molecules on the metal nanoparticles surface. Finally these platforms were employed in the selective and sensitive detection of chlorinated pesticides which can be inserted in the multilayers of dithiols formed between NPs in hot spots.