Imaging of ATP membrane transport with dual micro-disk electrodes and scanning electrochemical microscopy.

Extracellular adenosine-5'-triphosphate (ATP) is involved in a variety of relevant regulatory mechanisms at a cellular level and has therefore been focus of extensive research. One of the major challenges associated with measuring this key regulatory analyte is the ability to detect and localize extracellular ATP with sufficient spatial and temporal resolution in physiological environments. In this study, scanning electrochemical microscopy (SECM) utilizing an amperometric micro-biosensor based on co-immobilization of the enzymes glucose oxidase and hexokinase is applied for imaging ATP transport through a porous polycarbonate membrane under physiologically relevant conditions. The enzymatic biosensor operates on competitive consumption of the substrate glucose between the immobilized enzymes glucose oxidase and hexokinase involving ATP as a co-substrate. Quantitative determination of the ATP concentration is based on a linear correlation between the glucose consumption and the ATP level. Integration of the amperometric ATP micro-biosensor into a dual micro-disk electrode configuration is achieved by immobilizing the enzymes at one of the micro-disk electrodes while the second disk serves as an unmodified amperometric probe for controlled positioning of the micro-biosensor in close proximity to the sample surface enabling quantification of the obtained current signal.