A novel method to directionally stabilize enzymes together with redox mediators by electrodeposition

• Directionally immobilize enzymes onto microelectrode of interest.
• High modification selectivity without contaminating other electrode sites.
• 2nd generation microbiosensors for detecting H2O2, glucose, and glutamate.
• Sensitivity towards H2O2 was 5.274 nA μM−1 mm−2, towards glucose 2.65 nA μM−1 mm−2, and towards glutamate 0.33 nA μM−1 mm−2.

This paper depicts a novel method to directionally stabilize enzymes together with redox mediators by electrodeposition. Chitosan was used as a stabilizing matrix. By electrochemical removal of local H+, chitosan close to working electrode became locally insoluble, and enzymes and redox mediators in chitosan were stabilized. The microelectrode on home-made microelectrode array (MEA) served as the working electrode. Three model enzymes––horseradish peroxidase (HRP), glucose oxidase (GOD), and glutamate oxidase (GlOD)––were used to fabricate different biosensors, and the redox mediator model was a poly(vinylpyridine) complex of Os(bpy)2Cl and a diepoxide (PVP-Os). Biosensors fabricated by the method exhibited very high performance. For HRP biosensor fabricated by this method, the sensitivity was 5.274 nA μM−1 mm−2, with linear detection range (LDR) of 2–220 μM and limit of detection (LOD) of 1 μM (S/N=3); for GOD biosensor, the sensitivity was 2.65 nA μM−1 mm−2, with LDR of 4–500 μM and LOD of 2 μM (S/N=3); for GlOD biosensor, the sensitivity was 0.33 nA μM−1 mm−2, with LDR of 4–500 μM and LOD of 2 μM (S/N=3). Since this method is very simple and especially suitable for directionally introducing enzymes and redox mediators onto microelectrode without contaminating other sites in the same microenvironment, it could be used for fabricating in vivo or in vitro 2nd generation biosensors in μm-scale, especially in neuroscience.