Immobilized diaphorase surfaces observed by scanning electrochemical microscope with shear force based tip-substrate positioning

Imaging of a coimmobilized diaphorase and albumin surface was investigated by scanning electrochemical microscopy (SECM) with shear force based tip-substrate distance control. A microelectrode tip was attached to a commercially available tuning fork to detect the shear force between the microelectrode tip and the surface. We used the standing approach mode, which repeats an approach and retraction at each data point of the surface to obtain simultaneous current and topographic images. To check the performance of our SECM system, we imaged a platinum-patterned array electrode and a diaphorase/albumin coimmobilized glass surface. Since the system acquires current when the tip is retracted to a desired distance, this mode is useful for a relatively large microelectrode (similar to 10 mu m) and for scanning a large area (few hundreds of micrometers). Furthermore, by retracting the tip when the tip moves laterally to the next data point to avoid contact between the tip and sample surface, we successfully imaged the surface without destroying its morphology.