Gas Diffusion Electrodes for Use in an Amperometric Enzyme Biosensor

The preparation of gas diffusion electrodes and their use in an amperometric enzyme biosensor for the direct detection of a gaseous analyte is described. The gas diffusion electrodes are prepared by covering a PTFE membrane (thickness 250 mu m, pore size 2 mu m, porosity 35%) with gold, platinum, or a graphite/PTFE mixture. Gold and platinum are deposited by e-beam sputtering, whereas the graphite/PTFE layer is prepared by vacuum filtration of a respective aqueous suspension. These gas diffusion electrodes are exemplarily implemented as working electrodes in an amperometric biosensor for gaseous formaldehyde containing NAD-dependent formaldehyde dehydrogenase from P. putida [EC. 1.2.1.46] as enzyme and 1,2-naphthoquinone-4-sulfonic acid as electrochemical mediator. The resulting sensors are compared with regard to background current, signal noise, linear range, sensitivity, and detection limit. In this respect, sensors with gold or graphite/PTFE covered membranes outclass ones with platinum for this particular analyte and sensor configuration.