In cell culture research and biotechnology, precise pH monitoring is crucial for maintaining cellular health and ensuring reliable experimental outcomes. Traditional pH measurement methods, such as glass electrodes and chemical indicators, are often limited by issues such as fragility, calibration requirements, and potential cytotoxicity. This study presents a novel pH sensor based on bacteriorhodopsin (bR), a light-sensitive protein that undergoes conformational changes in response to pH fluctuations, generating a measurable photoelectric signal. The integrated bR-based electrochemical electrode in a flexible pH biosensor is demonstrated, with measurements spanning the physiological pH range of 6.0-8.5. The sensor shows a high correlation (R