A novel low-noise measurement principle for LAPS and its application to faster measurement of pH

A novel measurement principle for the light-addressable potentiometric sens or (LAPS) system is proposed in this paper. With several features like low- noise and low-background, this measurement scheme extends the application o f LAPS in faster high-sensitive direct monitoring of ionic concentration an d small change in the surface potential without the need of costly instrume nts like potentiostat, lock-in amplifier. Using two out-of-phase modulated light sources applied at two different points of the Si surface of the hete rostructure, a kind of differential LAPS response is obtained. Due to the a ddition of the two out-of-phase photocurrents, low-frequency components ass ociated with the photocurrents are canceled out and a low-noise and hence h ighly sensitive response is expected. As an application of the new principl e, the pH measurement of an electrolyte solution is investigated and a new instrumentation for the direct, high-sensitive, and faster measurement of p H is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.