Potentiostatic biosensors are a type of electrochemical biosensor that utilize a potentiostat to detect the voltage difference between the working electrode (WE) and reference electrode (RE). This is achieved by adjusting the potential difference of the counter electrode with respect to the working electrode, while the resultant potential difference is determined by the concentration of an analyte. A new lightaddressable potentiometric sensor (LAPS) system was developed for detecting the model biomarker, human immunoglobulin G (hIgG). The system utilized goat anti-human immunoglobulin G antibody as a recognition element that was covalently immobilized on the surface of the LAPS chip. The light-addressable capability of the LAPS system enabled the detection of hIgG dissolved in the supporting electrolyte solution by monitoring potential shifts of the sensor. To produce a stable photocurrent, a laser diode controlled by a field-programmable gate array was used as the light emitter to drive the LAPS. The potential shift response showed a linear correlation with the concentration of hIgG, with a regression equation of ΔV (V) = 0.00714ChIgG (μg/mL)-0.0147 and a correlation coefficient of 0.9968 over a range of 0-150 μg/mL. The X-ray photoelectron spectroscopy data confirmed that the hIgG antibodies were successfully immobilized on the LAPS chip surface, and hIgG was captured by the goat anti-human IgG. Specificity tests proved a highly specific interaction between hIgG and its antibodies. Furthermore, the LAPS system demonstrated acceptable stability and reproducibility, making it more applicable to the detection of disease biomarkers. This study proposed a promising strategy for the detection of multi-biomarkers by extending the sensing surface membrane lifetime and fabricating array LAPS biosensors in the future. The LAPS system reported here offers a simple operation and multiple-sample format, which could have great potential in various environmental, food, and clinical applications.