Phase-mode LAPS and its application to chemical imaging

The light-addressable potentiometric sensor (LAPS) is a chemical sensor based on the field effect in the electrolyte–insulator–semiconductor (EIS) structure. In the conventional LAPS, the ion concentration in the analyte solution in contact with the sensing surface is determined by measuring the amplitude of the photocurrent induced by illumination. In this study, we developed the phase-mode LAPS, in which the phase of the alternating photocurrent is measured instead of its amplitude. The phase–voltage curve shifted along the voltage axis in response to the variation of the ion concentration in analogy to the shift of the amplitude–voltage curve in the conventional LAPS. The primary advantage of the phase-mode LAPS is that it is much less sensitive to the variation of the light intensity. It is also demonstrated that chemical imaging based on the phase-mode LAPS is free from artifacts related to defects in the semiconductor substrate.