Development of unconventional technologies for wireless collection andanalysis of quantitative, clinically relevant information on physiologicalstatus is of growing interest. Soft, biocompatible systems are widely regardedas important because they facilitate mounting on external (e.g., skin) andinternal (e.g., heart and brain) surfaces of the body. Ultraminiaturized,lightweight, and battery-free devices have the potential to establish comple-mentary options in biointegration, where chronic interfaces (i.e., months)are possible on hard surfaces such as the fingernails and the teeth, withnegligible risk for irritation or discomfort. Here, the authors report materialsand device concepts for flexible platforms that incorporate advanced opto-electronic functionality for applications in wireless capture and transmis-sion of photoplethysmograms, including quantitative information on bloodoxygenation, heart rate, and heart rate variability. Specifically, reflectancepulse oximetry in conjunction with near-field communication capabilitiesenables operation in thin, miniaturized flexible devices. Studies of the mate-rial aspects associated with the body interface, together with investigationsof the radio frequency characteristics, the optoelectronic data acquisitionapproaches, and the analysis methods capture all of the relevant engineeringconsiderations. Demonstrations of operation on various locations of the bodyand quantitative comparisons to clinical gold standards establish the versa-tility and the measurement accuracy of these systems, respectively.