  This study proposes a novel design of glucose sensor with enhanced
selectivity and sensitivity by using graphene Schottky diodes, which is
composed of Graphene (G)/Platinum Oxide (PtO)/n-Silicon (Si) heterostructure.
The sensor was tested with different glucose concentrations and interfering
solutions to investigate its sensitivity and selectivity. Different structures
of the device were studied by adjusting the platinum oxide film thickness to
investigate its catalytic activity. It was found that the film thickness plays
a significant role in the efficiency of glucose oxidation and hence in overall
device sensitivity. 0.8-2 uA output current was obtained in the case of 4-10 mM
with a sensitivity of 0.2 uA/mM.cm2. Besides, results have shown that 0.8 uA
and 15 uA were obtained by testing 4 mM glucose on two different PtO
thicknesses, 30 nm, and 50 nm, respectively. The sensitivity of the device was
enhanced by 150% (i.e., up to 30 uA/mM.cm2) by increasing the PtO layer
thickness. This was attributed to both the increase of the number of active
sites for glucose oxidation as well as the increase in the graphene layer
thickness, which leads to enhanced charge carriers concentration and mobility.
Moreover, theoretical investigations were conducted using the Density Function
Theory (DFT) to understand the detection method and the origins of selectivity
better. The working principle of the sensors puts it in a competitive position
with other non-enzymatic glucose sensors. DFT calculations provided a
qualitative explanation of the charge distribution across the graphene sheet
within a system of a platinum substrate with D-glucose molecules above. The
proposed G/PtO/n-Si heterostructure has proven to satisfy these factors, which
opens the door for further developments of more reliable non-enzymatic
glucometers for continuous glucose monitoring systems.
