For the analysis of serum samples, we found that the effects of the complex sample matrix and increased viscosity hinder the comparison with predetermined calibration values. Accordingly, we used the standard addition method, which has been shown to effectively mitigate matrix contributions in calibration-free protocols . We analysed three serum samples and found alkaline phosphatase activities of 35±1, 105±6 and 8±4 U L -1 (Fig. and). Remarkably, and despite the large surface area of LIG-E, we did not observe considerable electrode fouling in serum tests. We attribute this to the low-volume requirements and the regeneration of electrode surface by the buffer flow. We benchmarked against the gold standard test, a plate reader monitoring absorption kinetics with p-nitrophenyl phosphate as a substrate (Figs. S16 and S17), and observed excellent agreement (33.6±0.6, 106.7±0.5 and 7.4±0.1 U L -1 , respectively; Fig. ) between the datasets.