Clear Patch: Transparent Wearable Sensors for Human and Plant Health Monitoring.

Wearable sensors are essential tools for the continuous, real-time monitoring of human and plant health. They interact directly with skin and living plant organs to track physical, electrical, and chemical signals that are often difficult to measure with off-body or off-plant sensors. Sensors that are optically transparent minimize interference with the host. Achieving transparency is challenging because devices must minimize light absorption, haze, and color tint while maintaining good conductivity, mechanical flexibility, strong adhesion, and breathability. This Review focuses on transparent wearable sensors in which optical transparency is functionally important for living-interface operation, including optical access, unobtrusive wear, multimodal readout, or reduced perturbation of plant photosynthesis. We include device-level demonstrations that integrate transparent or semitransparent substrates, electrodes, encapsulants, or sensing layers with human skin, microneedle interfaces, or plant organs, while excluding opaque wearables, nonwearable transparent electronics, and rigid transparent electrodes without sensing integration. We categorize different transparent components needed for a wearable sensor, including transparent insulators, electrodes, and sensing materials, and relate these components to human use and emerging plant health applications. In contrast to prior reviews, which largely treat transparency as a material property and survey human or plant wearables separately, we frame transparency as a system-level design requirement that unifies both domains, clarifying where optical neutrality is functionally necessary and what should be reported to make transparency a comparable design variable.