Towards blood free measurement of glucose and potassium in humans using reverse iontophoresis

Non-invasive patient monitoring by reverse iontophoresis has the potential to drive improved treatment of a variety of conditions within many healthcare settings. We have focussed on the application of this sensor technology to the monitoring of diabetes and cardiovascular disease. Effective monitoring of glucose and potassium levels is crucial to the effective management of these conditions, and the ultimate aim of our study was to investigate the transdermal extraction of these molecules using reverse iontophoresis. Using a novel ethanol enhanced skin gel patch we have recently developed, we applied a low level current (100 μA/cm2) across the skin of nine healthy volunteers for two separate 60 min periods, and quantified the glucose and potassium extracted into the gel, using photometric and electrochemical means respectively. Subjects were in a fasted state during the first 60 min measurement period, while the second measurement period followed the ingestion of a high glucose drink. Finger stick blood samples were obtained at regular intervals during the procedure and these were analysed for glucose and potassium using standard clinical assays. We found that both potassium and glucose were extracted across the skin in readily quantifiable amounts, and the extraction methodology displayed sensitivity to relatively small changes in analyte levels within the blood. We also investigated potassium as an internal standard, and although it improved the correlation between blood and transdermal glucose measurements, alternative calibration approaches will be necessary if the level of accuracy required for clinical application of this sensor technology is to be realised.