Developement of a novel laser-beam-scanning bio-chemical sensing microscope

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A novel chemical imaging microscope has been developed with the aid of the present grant. The chemical imaging microscope is based on the principle of the light-addressable potentiometric sensor (LAPS). The sensing surface of a LAPS device in contact with the electrolyte is made of insulating Si _3N_4 film deposited on semiconducting Si substrate. The two-dimensional chemical information in the electrolyte is mapped into the variation of the width of depletion layr in Si substrate. The electrical impedance of the depletion layr is measured as a function of position, in the form of photocurrent induced by scanning-laser-beam that illuminates the rear surface of the Si substrate.The spatial resolution, sensitivity and measurement speed have been investigated and improved to be 10 micron meter, 0.01pH and 100 pixels/sec, respectively.The microscope has been verified to have capability of visualization of two-dimensional bio/chemical information in electrolytic specimens ; distribution of pH of microorganism colonies, specific molecules and redox potential.It could be also used for imaging rapidly changing electrical-potential such as active neuron potential. To demonstrate its applicability to faster processes, we measured the chemical waves in Belousov-Zhabotinsky reaction. Propagation of chemical waves was observed as variation of redox potential either at a fixed point or on a line along the propagating direction. Such measurement would be useful for microscopic analysis of reaction-diffusion and pattern-formation phenomena in redox reaction systems.