HIGH-RESOLUTION PH IMAGING SENSOR FOR MICROSCOPIC OBSERVATION OF MICROORGANISMS

We have constructed a high-resolution pH imaging sensor, which enables one to observe the metabolic activity of microorganisms microscopical ly. A spatial resolution better than 10 mu m was achieved by thinning the Si substrate to 20 mu m, and by employing an infra-red laser as an illumination source. Using a 100 kHz digital sampling technique for s ignal detection, a pH image of 128 x 128 pixels was measured within 15 min. The pH imaging sensor was integrated into a system for microscop ic observation of incubated biological specimens such as microorganism s. Using the pH imaging sensor, Escherichia coli (E. coli) colonies in cubated on agar medium for 8 h (visual size similar to 0.2 mm diameter , number of cells similar to 800) were detected. The observed pH distr ibution was in agreement with the result of simulation based on the pr oduction and diffusion of acidic ions.