Synthesis of flexible free-standing silver nanoparticles-graphene films and their surface-enhanced Raman scattering activity

A free-standing and flexible silver nanoparticles-graphene (Ag NPs–GE) film with high surface-enhanced Raman scattering (SERS) sensitivity has been developed. First, the high stable and dispersive Ag NPs–GE composite was fabricated by in situ reduction using graphene oxide sheets as substrates and the hydrazine hydrate as a reducing agent in the solvothermal environment. Second, the Ag NPs–GE films can be fabricated through vacuum filtration of the Ag NPs–GE suspension. Transmission electron microscope (TEM) images show that the Ag NPs with an average size of 22 nm and a narrow particle size distribution are uniformly distributed on GE sheets. The coverage density of Ag NPs onto the surface of GE sheets can be successfully controlled by tuning the concentration of silver ion precursor. As-prepared Ag NPs–GE substrates have good SERS sensitivity due to the high SERS-active of Ag NPs. The enhancement factor for 1 × 10⁻⁶ M of rhodamine 6G molecules adsorbed onto the surface of substrate is about 2.7 × 10⁵. The SERS activity toward crystal violet and Escherichia coli was also investigated.