Dual Imaging of Topography and Photosynthetic Activity of a Single Protoplast by Scanning Electrochemical Microscopy

Two types (A and B; see Figure 1 in the text) of dual-Pt microdisk electrodes (disk radius, 0.5−4.0 μm; whole tip radius, 5.0−15 μm) were fabricated to simultaneously detect two electroactive species near a single algal protoplast (radius, 25 μm). At the tip of type A, the two disks were on the same plane. Two disk planes of electrode type B formed an angle of ∼135° at the tip. Cyclic voltammetric investigation indicated that, compared with type A, one disk in type B only slightly collected the species electrogenerated at the other disk. These dual-microdisk electrodes were applied to electrochemical measurements of a single protoplast in artificial seawater. The topographic profiles of the single protoplast were obtained from the variation of oxidation current for 1.0 mM Fe(CN) 6 4 - at one disk. The photosynthetic oxygen generation from the protoplast was also monitored by detecting the reduction current for oxygen at another disk. The electrode of type B was used as a probe for scanning electrochemical microscopy (SECM) to obtain dual-SECM images of topography and activity of a single protoplast.