Reduced Graphene Oxide-Coated Silica Nanospheres as Flexible Enzymatic Biosensors for Detection of Glucose in Sweat

Noninvasive flexible electrochemical sensors for body fluid analysis are subject to strict requirements for sensitivity and detection limit. In this work, a three-dimensional (3D) flexible biosensor based on reduced graphene oxide (rGO) nanocomposites was fabricated for detecting glucose in sweat. Graphene oxide (GO) nanosheets were first assembled onto the surface of silicon dioxide (SiO2) nanospheres by electrostatic interaction and in situ reduced by tannic acid (TA) to obtain the electroactive rGO/SiO2 nanocomposites. The 3D flexible biosensors were then prepared by successive dropping of the rGO/SiO2 nanocomposites, glucose oxidase (GOx), and Nafion (NF) solution on the conductive substrate (C-PDMS) composed of a carbon nanotube film and polydimethylsiloxane. Herein, the 3D electroactive structure was designed to maximize the specific surface area of the biosensor, significantly increasing the sensing and recognition sites. The NF/GOx/rGO/SiO2/C-PDMS biosensor exhibited good linear detection of glucose in the range of 0.1–9 mM with a sensitivity and lower detection limit of 60.8 μA mM–1 cm–2 and 3.7 μM, respectively, which is superior to existing sensors. Moreover, the biosensor performed well in the detection of glucose from sweat samples and is expected to be used in clinical analysis, offering a new design strategy for point-of-care testing of target molecules.