Two-photon polymerization of optical microresonators for precise pH sensing

In water monitoring, environmental analysis, cell culture stability, and biomedical applications, precise pH control is demanded. Traditional methods like pH strips and meters have limitations: pH strips lack precision, while electrochemical meters, though more accurate, are fragile, prone to drift, and unsuitable for small volumes. In this paper, we propose a method for optical detection of the pH value based on the multiplexed sensor with 4D microcavities fabricated with two-photon polymerization. This approach employs pH-triggered reversible variations in microresonator geometry and integrates hundreds of dual optically coupled 4D microcavities to achieve the detection limit of 0.003 pH units. The proposed solution is a clear instance for the use-case oriented application of the two-photon polymerized structures of high optical quality. With benefits of the multiplexed imaging platform, dual 4D microresonators can be integrated alongside other microresonator types for pH-corrected biochemical studies.