Fabrication of free-standing graphene composite films as electrochemical biosensors

We report a simple fabrication method for large-scale free-standing graphene–gold nanoparticle and graphene-single wall carbon nanotube composite films by using a centrifugal vacuum evaporation followed by a thermal reduction process. The homogeneous mixture of a graphene oxide (GO) suspension with gold nanoparticle (Au NP) or single wall carbon nanotube (SWCNT) is self-assembled at the air/liquid interface, resulting in the multilayered GO–Au NP and GO–SWCNT composite films. The cross-sectional image reveals that the graphene layers are orderly stacked in the reduced GO–Au NP film, while the reduced GO–SWCNT film shows a randomly packed morphology due to the dominant π–π interaction between the side wall of SWCNTs and the GO surfaces. In particular, the reduced GO–Au NP film shows an increased electrode kinetics and cyclic voltammetric response in proportion to the amount of Au NPs, and 3-fold enhancement of anodic peak current was observed compared with that of the reduced GO films. We employed the reduced GO–Au NP film as a matrix to immobilize tyrosinase enzyme for phenol detection, and the phenol-induced electrochemical catalytic reaction can be monitored with 3-fold higher sensitivity than the reduced GO film, demonstrating great potential of graphene composite as an electrochemical enzyme biosensor for environmental pollutant screening.