Abstract: Detecting postoperative complications in a patient uses a substrate made of biocompatible or biodegradable material. An adhesive layer adheres the substrate to patient tissue, surgical tool, or medical device. A biosensor at the substrate detects or measures an analyte in the patient's body. The biosensor may be on the surface of the substrate or within a microchannel in the substrate. A separation or isolation structure may be provided to separate or isolate the analyte from other analytes prior to the biosensor. A microcontroller is disposed on the substrate and connected to the biosensor and to a wireless communications interface also disposed on the substrate. The microcontroller measures a signal from the biosensor and may perform an analysis on the measured signal. Measured data or data resulting from the analysis is transmitted through the wireless communications interface to a transdermal patch or other remote device for storage and display.