Glucose detection is clinically significant for diagnosis and management of diabetes. Its electrochemical detection can be realized by using glucose oxidase (GOD) as the mediator or recognition element. A conducting porous matrix, which gives large effective detection surface and high enzyme loading capacity, can be made by mixing RGO with supporting polymers.
A glucouse oxidase GOD–RGO–chitosan modified electrode based sensor that exhibited a wider linear range (from 0.08 mM to 12 mM), a lower LOD (0.02 mM), and a higher sensitivity (37.93 mA mM-1 cm-2) as compared with the sensors using other nanostructured materials was reported in the literature. The electron-transfer-rate constant (2.83 +/- 0.18 s-1) of this sensor is higher than that of multi-walled carbon nanotubes (MWCNTs) based sensors. Without using chitosan that may hinder electron transfer, a simple electrode with GOD adsorbed on RGO thin film was reported. It offers a LOD of 0.01 mM and sensitivity of 110.0 mA mM-1 cm-2.
A porous matrix with GOD, RGO, and polypyrrole (ppy) is also reported in literature. The ppy provides excellent conductivity, support to the matrix, and biocompatibility. A ultra-low LOD (3 mM) was reached.
A layer-by-layer (LbL) assembly of alternating RGO films and poly(ethyleneimine) (PEI) films with controllable film thickness, morphology, and composition has also been presented. Both glucose oxidase and glucoamylase were loaded into such LbL film to enable simultaneous detection of glucose and maltose, demonstrating the possibility of integrating RGO and multi-enzyme systems in a single multilayer film.
Various strategies have been developed to modify RGO. For instance, ionic liquids have been used to hybridize with RGO. Ionic liquids assist to disperse RGO for thin-film fabrication, and can serve as excellent binders between electrolyte and electrode because of their ability to promote electron transfer and ion exchange, their electrochemical stability and biocompatibility.
Au nanoparticles have been used to decorate RGO by in situ reduction or physical adsorption to improve LOD, detection range, and stability. Similarly, platinum nanoparticles have been electrochemically deposited on RGO and an outstanding LOD of 0.6 mM has been achieved for glucose detection.
RGO can also be modified by doping. The nitrogen-doped (N-doped) RGO film that possesses a large amount of positive charges can improve the electrochemical detection by enhancing adsorption of O2, H2O2 and other intermediates. A novel sensor based on a N-doped RGO/Chitosan/GOD/GCE hybrid was also reported in the literature. It has a detection limit as low as 10 mM. The reduction potential of the electrode was shifted by 400 mV towards positive potential as compared with a bare GCE, indicating its fast electron transfer kinetics.
Extracted and edited from “Biological and chemical sensors based on graphene materials by Yuxin Liu, Xiaochen Dong and Peng Chen in Chemical Society Reviews, 2012″