Molecular sensitivity of metal nanoparticles decorated graphene‐family nanomaterials as surface‐enhanced Raman scattering (SERS) platforms

Abstract

Abstract Graphene‐mediated surface enhanced Raman scattering is a recent phenomenon that produces clean and reproducible signals from chemical analytes. In this work, we report on the development of graphene‐family nanomaterials (graphene oxide; GO, reduced GO; rGO, and multilayer graphene; MLG) decorated with physisorbed silver (AgNP) and gold (AuNP) nanoparticles and as layered architectures for detection of methylene blue and rhodamine 6G dyes in view of optical and biological significance. The experimental results illustrate four orders of magnitude graphene‐mediated surface enhanced Raman scattering enhancement in the order rGO/AgNP > GO/AgNP > MLG/AgNP for physisorbed and cascade amplified signal on multilayer architectures, larger than those only on graphene and metal nanoparticles, which is achieved at optimal size of Ag (30 nm) and Au (40 nm) on rGO. Moreover, highly‐sensitive graphene‐decorated nanoparticle are capable of molecular detection over a broad concentration range 10 pM–100 μM. The findings are discussed in terms of (a) strong graphene‐metal nanoparticle coupling leading to local interfacial hybridization and polarization, (b) molecular structural symmetry of analytes in relation to nanoparticle‐graphene functionalities, and (c) effective charge transfer and exchange or sharing of charges between analyte and nanoparticles decorated graphene. Optimized metal nanoparticle‐graphene geometries and electronic properties are determined from density functional theory calculations. They identify preferred metal nanoparticle adsorption sites and long‐range electrostatic interactions and determine relative resonant charge transfer population (alternatively, chemical enhancement mechanism) values derived from the Mulliken population thus gaining insights into effective enhancement factors. These findings will help to design advanced SERS platforms for ultrasensitive detection of chemicals and biological molecules useful in bio‐nanotechnology.