Graphene/Amorphous MIL-101(Cr)-NH2 Double Layer Composite for Nonenzymatic Sweat Glucose Sensing by Voltammetry and Chronoamperometry

Herein, we report a novel electrochemical sensor for determining glucose in sweat, employing a graphene/metal-organic framework (MOF) as a modifier for stainless steel (SS) electrode. The MOF structures, MIL-101(Cr), MIL-101(Cr)-NO2, and MIL-101(Cr)-NH2, were hydrothermally synthesized and then characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, N2 adsorption/desorption isotherms, and scanning electron microscopy (SEM). XRD and SEM results proved the formation of the crystalline MIL-101(Cr) and MIL-101(Cr)-NO2, and the amorphous MIL-101(Cr)-NH2. Additionally, FT-IR and isotherms confirmed their composition and mesoporosity, respectively. The amorphous MIL-101(Cr)-NH2 showed the best electrocatalytic activity towards glucose oxidation among the fabricated MOFs. The electrocatalytic activity was also boosted after incorporating conductive graphene. Under optimized conditions, graphene/MIL-101(Cr)-NH2/SS was used for glucose determination using square wave voltammetry and chronoamperometry with detection limits of 0.004 and 0.01 mM, respectively. Moreover, the modified electrode showed acceptable recovery values when it was applied to detect glucose in artificial sweat samples.