Body‐integrated photonic biosensors: Illuminating the path to active healthcare

Abstract Body‐integrated photonic biosensors are emerging as key enablers of active healthcare, offering sensitive, selective, and potentially multiplexed optical readouts in wearable, implantable, and ingestible formats. Enabled by mechanically compliant, miniaturized designs, these platforms support point‐of‐care testing and continuous monitoring while reducing dependence on bulky benchtop instrumentation. This review summarizes major photonic biosensing modalities—fluorescence, colorimetry, surface plasmon resonance (SPR), localized SPR (LSPR), surface‐enhanced Raman scattering, and light‐modulating material (LMM)‐based sensing—highlighting their transduction principles, performance advantages, and practical constraints for on‐body operation. We then survey representative device implementations across five form factors, including flexible skin patches, optical fibers, contact lenses, miniprobes, and capsules, emphasizing target biofluids and biomarkers (e.g., sweat, wound exudate, tears, interstitial fluid, and blood) and key enabling integrations such as microfluidics, soft materials, and wireless readout. Finally, we discuss translational challenges, including robustness to ambient light and motion, sampling and calibration in unconstrained settings, long‐term stability and biocompatibility, expanded biomarker coverage, miniaturization and multifunctional integration, and the need for standardized benchmarking and clinical validation. We conclude with an outlook on standardization, scalable manufacturing, and data/AI‐assisted signal processing as critical directions for accelerating the adoption of body‐integrated photonic biosensors for continuous, personalized health monitoring.