Fig. 5. (a) Current status and future challenges for mimicking the complex enzyme system. (b) Schematic illustration of a two-step reaction taking place in the GSHA system. (c) Formation of oxTMB in the GSHA or oxidase–peroxidase coupled enzyme system in phosphate buffer (0.5 mM, pH 7.0), ([TMB] = 1 mM, [GS, GSA, GSH, GSAH, GSHA] = 1 mg mL^–1, [glucose] = 200 mM for artificial enzyme or 4 mM for natural enzyme, [GOx] = 100 μg mL^–1, [HRP] = 1 ng mL^–1).