Enzymatic biosensing by covalent conjugation of enzymes to 3D-networks of graphene nanosheets on arrays of vertically aligned gold nanorods: Application to voltammetric glucose sensing

The authors demonstrate efficient direct electron transfer from the enzyme glucose oxidase to vertically aligned gold nanorods with a diameter of similar to 160 nm and a length of similar to 2 mu m that are covalently linkage to a 3-dimensional network of reduced graphene oxide nanosheets. The assembly can be prepared by a 2-step electrochemical procedure. This hybrid structure holds the enzyme in a favorable position while retaining its functionality that ultimately provides enhanced performance for enzymatic sensing of glucose without utilizing mediators. The nanorod assembly was applied to the voltammetric detection of glucose. Figures of merit include an electrochemical sensitivity of 12 mu A.mM(-1).cm(-2) (obtained from cathodic peak current at a voltage of -0.45 V vs. Ag/AgCl), a 3 mu M detection limit (at signal/noise = 3), and a wide linear range (0.01-7 mM). The hybrid nanostructure has a heterogeneous electron transfer rate constant (ks) of 2.9 s(-1). The high electrochemical activity is attributed to the synergistic effect of a large active surface and an enhanced electron transfer efficiency due to covalent amide linkage.