Enzyme-based glucose sensors can be affected by environmental factors. For example, the mechanical deformation of wearable sensors during daily activities may lead to fractures in the sensor electronics that cause them to malfunction. The lactic acid present in sweat reduces the pH to 4–5, which affects the accuracy of enzyme-based sensors, as do variations in the ambient temperature. Therefore, a glucose monitoring system needs to be mechanically deformable, with correction of the results in real time based on simultaneous measurements of the pH and temperature. It would also be advantageous if the device were transparent, to make it discreet in use, and if microneedles were used for drug delivery, which would make the process painless.
Our recently developed graphene-based diabetes patch provides a potential solution to meet these needs (see Figure 1).9 The patch consists of multiple sensors, actuators, and sweat-control layers for the systematic collection of sweat, sensing of glucose, and feedback-controlled transdermal drug delivery. First, a layer for the uptake of sweat absorbs secreted sweat, of which the amount is monitored by an integrated humidity sensor. When the relative humidity exceeds 80%, other sensors (for example, glucose, pH, and temperature sensors) begin their measurements. The pH and temperature sensors measure the pH of sweat and the ambient temperature, respectively. These environmental parameters are used to correct the glucose concentration in sweat, which is measured by an integrated glucose sensor, in real time.