Pd-Doped WO3 Nanostructures as Potential Glucose Sensor with Insight from Electronic Structure Simulations

Herein, we report the results of crystal-structure-dependent nonenzymatic glucose-sensing properties of tungsten oxide (WO3) and Pd-doped WO3 nanostructures. The WO3 nanomaterials with orthorhombic, monoclinic, and mixed (ortho + monoclinic) phases were harvested by a facile hydrothermal route by varying the reaction time and subsequent annealing processes. Electrocatalytic activity tests of WO3 samples revealed a 3-fold oxidation peak current enhancement in the monoclinic Pd-doped WO3 nanobricks assembly as compared to the orthorhombic WO3 microspheres. Moreover, the Pd-doped WO3 showed a higher glucose-sensing performance in terms of the detection sensitivities of 11.4 μA μM-1 cm-2 (linear range: 5-55 μM) and 5.6 μA μM-1 cm-2 (linear range: 65-375 μM). We have also performed density functional theory simulations for the monoclinic WO3 and Pd-doped WO3 to investigate the charge-transfer and bonding mechanism of glucose on WO3 and Pd-doped WO3 surface. As the binding energy of glucose is higher in the case of Pd-doped WO3 as compared to bare WO3, it becomes more conducting due to enhancement of density of states near Fermi level; theoretically, we can predict that Pd-doped WO3 exhibits a better charge-transfer media compared to bare WO3, resulting in enhanced glucose-sensing performance, which, in turn, qualitatively supports our experimental data. Hence, our experimental data and theoretical insight from the electronic structure simulations conclude that Pd-doped monoclinic WO3 is a potential material for the fabrication of real-time glucose sensors.