Clinical Evaluation of a Continuous Minimally Invasive Glucose Flux Sensor Placed over Ultrasonically Permeated Skin

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Abstract
Frequent monitoring and tight metabolic control of blood glucose levels can reduce microvascular complications and subsequent co-morbidities in patients with diabetes. Self-monitoring with finger sticks provides intermittent data at best, and results in poor compliance. We report on a minimally invasive system that continually measures glucose flux through ultrasonically permeated skin. Ten patients with diabetes were enrolled in a clinical study to determine correlation between data collected by glucose biosensors placed over ultrasonically treated skin sites (two per patient), and blood glucose readings were taken every 20 min over an 8-h period. Glucose flux biosensors measured amperometric current proportional to hydrogen peroxide level, generated from catalytic conversion of glucose by glucose oxidase; the sensor was coupled to the skin by a thin hydrogel containing an osmotic extraction buffer, creating a gradient for glucose transport through the skin. The biosensors were attached to small portable meters that recorded time, current, and temperature readings every 5 s. At the conclusion of the study period, meter recordings were downloaded for data processing. Skin sites were examined for irritation due to biosensor contact. Data from glucose biosensors with completed data sets had a correlation coefficient of 0.84, and 95% of the data pairs (n = 241) were in the A + B region of a Clarke error grid. Ultrasonic pretreatment lasting about 10 s resulted in improved conductance in all patients. No patients complained of pain or irritation at any time during the study. Continuous monitoring of glucose flux through ultrasonically permeable skin is safe and feasible.