A light-addressable potentiometric sensor (LAPS) is a chemical sensor that is based on the field effect in an electrolyte-insulator-semiconductor structure. It requires modulated illumination for generating an AC photocurrent signal that responds to the activity of target ions on the sensor surface. Although high-power illumination generates a large signal, which is advantageous in terms of the signal-to-noise ratio, excess light power can also be harmful to the sample and the measurement. In this study, we tested different waveforms of modulated illuminations to find an efficient illumination for a LAPS that can enlarge the signal as much as possible for the same input light power. The results showed that a square wave with a low duty ratio was more efficient than a sine wave by a factor of about two.
Keywords: LAPS; duty ratio; field-effect device; light-addressable potentiometric sensor; lock-in detection; modulated illumination; pH sensor; photocurrent; square wave; waveform.