Two-photon polymerization of optical microresonators for precise pH sensing

Abstract

Water monitoring, environmental analysis, cell culture stability, and biomedical applications require precise pH control. Traditional methods, such as pH strips and meters, have limitations: pH strips lack precision, whereas electrochemical meters, although more accurate, are fragile, prone to drift, and unsuitable for small volumes. In this paper, we propose a method for the optical detection of pH based on a multiplexed sensor with 4D microcavities fabricated via 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 example of the use-case-oriented application of two-photon polymerized structures of high optical quality. Owing to the benefits of the multiplexed imaging platform, the dual 4D microresonators can be integrated with other microresonator types for pH-corrected biochemical studies.