A Liquid Crystal Integrated Skin pH Sensing Patch Enabled by Optical Coherence Tomography

Abstract Optical Coherence Tomography (OCT) is widely used for skin examination through structural imaging, but lacks the capability to measure biochemical parameters. In this study, a hydrogel patch that integrates with OCT to enable simultaneous structural imaging and biomedical information measurement of the skin is introduced. The hydrogel patch contains liquid crystal droplets that respond to biomedical information, e.g., pH changes by altering their molecular alignment, which is detectable in OCT images. This patch is calibrated and validated within a physiological pH range of 6.0–8.0, achieving a pH accuracy of ±0.2 units with transverse and axial imaging resolutions of 14.71 and 4.2 µm (in patch), respectively. Applying the patch to different areas of human skin reveals heterogeneous pH changes across regions, allowing for non‐invasive monitoring. This technology offers a superior, versatile, and user‐friendly solution for both clinical and research applications in dermatology, delivering structural and biomedical information within a single setup.