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 sensor (LAPS) system is proposed in this paper. With several features like low-noise and low-background, this measurement scheme extends the application of LAPS in faster high-sensitive direct monitoring of ionic concentration and small change in the surface potential without the need of costly instruments like potentiostat, lock-in amplifier. Using two out-of-phase modulated light sources applied at two different points of the Si surface of the heterostructure, a kind of differential LAPS response is obtained. Due to the addition of the two out-of-phase photocurrents, low-frequency components associated with the photocurrents are canceled out and a low-noise and hence highly sensitive response is expected. As an application of the new principle, the pH measurement of an electrolyte solution is investigated and a new instrumentation for the direct, high-sensitive, and faster measurement of pH is proposed.