High Sensitivity of Non-Invasive Glucose Sensors Made from Graphene-Based Composite Materials

The object of study was human sweat-based sensors printed on paper and spunlace nonwoven fabric using ink consisting of graphene and the conductive polymer PEDOT:PSS. In glucose identification, the 2D layers have demonstrated resistance decrease by three to five orders of magnitude. The influence of the printed layer structure on the sensor sensitivity has been established. A maximum sensitivity was observed for two to three printed layers, when most graphene flakes in the layers were located vertically and thus ensured presence of active states in the layer, at the flake boundaries. At elevated humidity, a spectrum of electrically active states appeared with a maximum at an energy of ~0.36–0.40 eV, and these electrically active states provided conductivity. It is assumed that adsorption of glucose molecules occurred on the edge states of graphene flakes, and they also acted as a catalyst for glucose oxidation. As a result, the conductivity increased sharply, depending on the additional carriers resulting from the glucose oxidation. The sharp decrease in the sensitivity and selectivity in thicker films of the same composite is associated with the change in the structure of the layers: there arise clusters of the material without free edge states of graphene flakes. The non-invasive sensors created combine ease of manufacture and low cost with high sensitivity.