Ag Nanoparticle-Decorated Graphene Oxide Coatings on the Inner Walls of Optofluidic Capillaries for Real-Time Trace SERS Detection

Surface-enhanced Raman scattering (SERS) is a rapid and nondestructive spectroscopic method for trace detection. The enhancement based on both electromagnetic and chemical mechanism requires the molecules to be in close contact with the SERS-active material. Therefore, it is difficult to detect trace amounts of molecules in liquid directly. In this paper, graphene oxide (GO) and Ag nanoparticles (AgNPs) are uniformly modified on the inner wall of the capillary. GO can provide chemical enhancement by adsorbing the analyte onto its flat surface and producing efficient charge transfer resonance with the analyte. AgNPs can provide strong localized surface plasmon resonance for electromagnetic enhancement, while capillary can shorten the molecular enrichment time and provide long light–analyte interaction length. The synergism of GO, AgNPs, and capillary makes the optofluidic platform have the ability of ultrasensitive and real-time detection. The detection limit of Rhodamine 6G and thiram is as low as 10–12 and 10–10 M, respectively, and the enhancement factor is as high as 0.9 × 1010 and 108, which indicates that the SERS-active capillaries have great potentials in real-time ultratrace detection of water environment pollutants.