  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.
