An electrochemical device with microwells for determining the photosynthetic activity of a single cyanobacterium

Electrochemical devices have been fabricated with 2 platinum (Pt) microelectrodes located at the bottom of microwells to characterize the photosynthetic activity of a single Microcystis viridis (cyanobacterium) cell. The cell was manipulated into the microwells by performing electrophoresis by applying dc voltage (typically 1.30 V peak-to-peak) to the Pt microelectrode. After removing the excess cells around the microwells, the microwells were covered using a urethane cover-plate, which blocked the diffusion of oxygen generated from the trapped cells thus leading to oxygen accumulation in the chamber. The cells trapped in the microwells were irradiated with a light-emitting diode light for 10 min to stimulate oxygen evolution by photosynthesis. The amount of oxygen accumulated in the chamber was determined by amperometry. The average rate of oxygen generation from a single cyanobacterium was calculated from the charge that was calculated from the responses and found to be at the level of 10−17 mol/s. Our system will be applicable to fundamental studies of cell biology and on-site monitoring of environmental toxicity.