ISFET sensor system for real-time detection of extracellular pH oscillations in slime mould

An ion sensitive field effect transistor (ISFET) array for the direct observation of physiochemical activity in a living biological specimen of a slime mould is demonstrated. The chip comprises a 64 x 64 pixel array of 10.2 x 10.2 mu m sensors. The device was fabricated in a standard 0.35 mu m foundry CMOS process. Using this device it was possible to observe periodic variations in pH consistent with the biological activity of slime mould with oscillatory amplitudes of 450 mu V +/- 70 mu V peak-to-peak, equating to 0.022 pH units at 20 mV/pH sensitivity, when taking data at a rate of 400 mu s per pixel-sample. These oscillations arise from intracellular Ca2+ variations giving rise to an extracellular pH change.