We have constructed a high-resolution pH imaging sensor, which enables one to observe the metabolic activity of microorganisms microscopically. A spatial resolution better than 10 μm was achieved by thinning the Si substrate to 20 μm, and by employing an infrared laser as an illumination source. Using a 100 kHz digital sampling technique for signal detection, a pH image of 128 x 128 pixels was measured within 15 min. The pH imaging sensor was integrated into a system for microscopic observation of incubated biological specimens such as microorganisms. Using the pH imaging sensor, Escherichia coli (E. coli) colonies incubated on agar medium for 8 h (visual size ∼0.2 mm diameter, number of cells ∼800) were detected. The observed pH distribution was in agreement with the result of simulation based on the production and diffusion of acidic ions.
- Chemical imaging sensor
- Light-addressable potentiometric sensor
- pH imaging sensor