Scanning chemical microscope for the visualization of a microscopic pH distribution

We have developed a scanning chemical microscope which enables the observation of a microscopic pH distribution to be made. With this microscope, a flat pH sensor made of silicon is functionally divided into microscopic multiple-measurement points, then, the pH of the electrolyte at each point is independently measured. The measured pH values are converted to a gray or color scale so that the pH distribution can be visualized. The measurement can be performed with a resolution down to 0.1 pH at spatial intervals of as little as 100 microns. The measurement time required for scanning 6.4 mm×6.4 mm is 30 s. Using this microscope we could obtain pH images showing the generation and expansion of a localized lower pH region due to the release of protons from a single cation-exchange resin particle placed on an agar electrolyte. The dependence of the expansion rate on the agar concentration was clearly observed. This microscope is expected to become one of the promising techniques of chemical imaging.