A quantitative look inside the body: minimally invasive infrared analysis in vivo.

Today's minimally invasive biosensors are often based on chemical reagents and suffer from, e.g., oxygen dependence, toxic reaction products, excess analyte consumption, and/or degradation of the reagents. Here, we show the first successful analyte quantification by means of a minimally invasive sensor in vivo, which does not use chemical reactions. The concentration of glucose is determined continuously in vivo using transcutaneous, fiber-based mid-infrared laser spectroscopy. When comparing the infrared data measured in vivo with the 127 reference readings of glucose obtained in vitro, an overall standard deviation of 17.5% and a median of the absolute values of the relative deviations of 11.0% are achieved. The encouraging results open up the path toward a reagent-free long-term implant for the continuous surveillance of metabolites. In addition, the high sampling rate facilitates important research in body metabolism as well as its application outside the field of medicine such as real-time analyte sensing during fermentation.