Lactate is a commonly used biomarker for sepsis5, with serum lactate levels > 4 mM/L indicating sepsis in adults. Results from point-of-care blood lactate tests allow discrete measurements to be made but cannot provide information quickly enough to inform clinical decisions such as drug dosing. Whereas continuous measurement of lactate would allow early detection of the onset of sepsis. Several point-of-care lactate sensors have been developed; however, none monitor lactate continuously and achieve a physiologically-relevant dynamic range within scope of lactate levels in critically-ill patients i.e. 1 –10 mM6.

We report a minimally invasive microneedle-based lactate biosensor to continuously monitor lactate concentrations in interstitial fluid (ISF). The microneedle biosensor will have a hydrogel layer of lactate oxidase enzyme which oxidises lactate to pyruvate, producing hydrogen peroxide, which is further oxidised at the electrode. To meet the physiologically-relevant concentration window, the extension of the sensor’s dynamic range will be demonstrated through the modification of the barrier membrane between the enzyme hydrogel layer and interstitial fluid. Koutecký–Levich analyses featuring a range of membrane materials will be reported and the sensor’s performance analysed over time. Finally, the sensor will be validated with in vivo results from a Phase I Clinical Study where exercise is used to generate lactate by healthy volunteers as a proof-of-concept before moving into monitoring of patients. Lactate generation in ISF will be compared to venous blood lactate and microdialysate7 lactate.