GOx/CNT/Silica Composites for Bioelectrodes

Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio

Sunday, June 01 2008

These composites could enable development of future biosensors and biofuel cells.

Composites of glucose oxidase (GOx), carbon nanotubes (CNTs), and biologically synthesized silica have been synthesized and tested. These composites are prototypes of biological/electrical interfacial materials and could enable the development of the next generation of devices for a variety of medical, scientific, industrial, and military applications. In particular, it is envisioned that materials based on these prototypes will be integrated into bioelectrodes for biosensors and biofuel cells.

The basic idea is to immobilize an enzyme (GOx) in a silica matrix intertwined with a CNT matrix that provides electrical conductivity between the enzyme and a carbon electrode substrate. In addition to holding the enzyme at the desired location, the immobilization of the enzyme in the matrix helps to electrochemically stabilize the enzyme. The electrical conductivity of the CNTs makes it possible to closely approach the ideal of direct electron transfer (DET) between the enzyme and the electrode substrate. For a biofuel cell, DET is advantageous because it obviates complex electron mediators that would otherwise be needed, thereby contributing to miniaturization of electrodes and maximization of output power. For a biosensor, DET is advantageous in that, at least theoretically, it enables an electrode to function in a potential range close to the redox potential of the enzyme.

GOx was chosen as the enzyme to be incorporated into the prototype composites because (1) it has been widely studied, especially with respect to DET and (2) as such, it serves as a suitable model material for the development of biosensors and fuel cells. In future development, other enzymes could be chosen to satisfy requirements in specific applications.