Silver nanocubes/graphene oxide hybrid film on a hydrophobic surface for effective molecule concentration and sensitive SERS detection

Abstract

Surface-enhanced Raman scattering (SERS) is a promising analytical technique with molecular “fingerprint” characteristic and high sensitivity. To achieve high sensitivity, analytes should be located in or around the so-called SERS “hot spots” that are normally formed in sub-10 nm gaps between the neighboring plasmonic nanostructures. Ordinary SERS substrates generally show low sensitivity to the molecules that have weak affinity to noble-metal surfaces. Here, we fabricate an effective SERS system that can concentrate and adsorb organic pollutants in water for sensitive SERS detection. Such a SERS platform is composed of a thin film of Ag nanocubes/graphene oxide hybrid covered on a small Cu foil, and the Cu foil is placed on a hydrophobic teflon surface. The Ag nanocubes/graphene oxide hybrid film is synthesized by growth of graphene oxide on a Cu foil using electrophoresis and subsequent assembly of Ag nanocubes on the graphene oxide in ethanol via van der Waals interactions. Organic pollutant molecules can be concentrated on the hybrid film by adding a droplet of aqueous analyte solution on the hybrid film and evaporating. Due to the hydrophobic nature of teflon surface, the droplet will shrink onto the hybrid film and realize the concentration of analyte molecules on a SERS platform. There exists large delocalized π-electron system in the graphene oxide, so the Ag nanocubes/graphene oxide hybrid can effectively adsorb a large number of analyte molecules. As there are plenty of nano-sized gaps between the Ag nanocubes that are densely attached on the graphene oxide sheets, high density SERS hot spots can be formed in the gaps. As a result, the Ag nanocubes/graphene oxide hybrid has shown high SERS activity with an enhancement factor of 3.9 × 108 and good signal uniformity (relative standard deviation ∼12%). It is further demonstrated that the hybrid SERS substrates have exhibited high SERS sensitivity to organic pollutants such as 4-chlorobiphenyl and methyl parathion, showing promising applicability in many fields as diverse as chemical analysis, environmental monitoring, and food safety inspection.