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Wearable physiochemical biosensors offer an exciting opportunity to monitor the concentration of ions and metabolites in bodily fluids such as sweat, saliva, and interstitial fluids for emerging applications in health and fitness monitoring [1]. However, current physiochemical sensing prototypes rely on batteries and DC-DC converters to provide power for instrumentation, which may result in a large, obtrusive form factor with limited lifetime [1]. This paper presents a wireless physiochemical sensing system capable of monitoring glucose or lactate when powered via an enzymatic biofuel cell (BFC) based on energy naturally present in the underlying analytes to be sensed. Unlike prior-art BFC harvesters, which utilize bulky boost converters to increase the 0.3-to-0.4V BFC voltage to a higher level suitable for conventional CMOS circuits [2], this work forgoes any DC-DC converter, and instead the entire system, including …