Conventional bioelectrical sensors and systems integrate multiple power harvesting, signal amplification and data transmission components for wireless biological signal detection. This paper reports the real-time biophysical and biochemical activities can be optically captured using a microscale light-emitting diode (micro-LED), eliminating the need for complicated sensing circuit. Such a thin-film diode based device simultaneously absorbs and emits photons, enabling wireless power harvesting and signal transmission. Additionally, owing to its strong photon-recycling effects, the micro-LED’s photoluminescence (PL) emission exhibits a superlinear dependence on the external conductance. Taking advantage of these unique mechanisms, instantaneous biophysical signals including galvanic skin response, pressure and temperature, and biochemical signals like ascorbic acid concentration, can be optically monitored, and it demonstrates that such an optoelectronic sensing technique outperforms a traditional tethered, electrically based sensing circuit, in terms of its footprint, accuracy and sensitivity. This presented optoelectronic sensing approach could establish promising routes to advanced biological sensors.