Mass transport limitations for electrochemical sensing in low-flux excretory fluids

Despite non-invasive instant monitoring of sweat metabolites is becoming a general trend in early diagnostics and screening, the reliability and accuracy of the on-skin electrochemical biosensors in real-life scenarios still remain questionable. As a rule, mass transport effects in scantily excreted liquids are ignored, when considering the design of such wearable setups. Here we provide a comprehensive investigation of the disruption factors for commonly used Prussian Blue based (bio)sensors under different hydrodynamic conditions (2 x 10-5 - 5 x 100 mm s-1 electrolyte velocity). A huge effect of flow on the (bio)sensors response has been revealed and explained with transport limitations for both analyte influx and reaction product outflux. It suggests no need for improving the sensor sensitivity, while minimizing analyte consumption and enhancing product withdrawal. Some strategies concerning measurement schemes and sensor design ensuring reliable sweat analysis have been discussed and illustrated for lactate and glucose on-skin monitoring.

Automated summary

Despite the increasing popularity of non-invasive instant monitoring of sweat metabolites, the reliability and accuracy of on-skin electrochemical biosensors in real-life situations are still uncertain. This study investigates the factors affecting the performance of commonly used Prussian Blue based sensors under different flow conditions. The results show that flow rate significantly impacts the sensor response, which can be attributed to limitations in analyte influx and reaction product outflux. Strategies for reliable sweat analysis, including measurement schemes and sensor design, are discussed and illustrated for lactate and glucose monitoring.