Improved Electrical Wiring of Glucose Oxidase Enzyme with an in-Situ Immobilized Mn(1,10-Phenanthroline)2Cl2‑Complex/Multiwalled Carbon Nanotube-Modified Electrode Displaying Superior Performance to Os-Complex for High-Current Sensitivity Bioelectrocatalytic and Biofuel Cell Applications

The search for a new and efficient transducer that can electrically connect enzyme active sites, like flavin adenine dinucleotide in glucose oxidase (GOx), with the electrode surface is a cutting-edge research area. Currently, Os­(bpy)-complex pendent polyvinyl­pyridine/polyvinyl imidazole/pyridinium hydrogel based chemically modified electrodes have been widely used for this purpose (bpy = 2,2’-bipyridine). Herein, we report, a [Mn2III(phen)4(O)­(Cl)2]2+ complex/Nafion-immobilized carboxylic acid-functionalized multiwalled carbon nanotube modified glassy carbon electrode (GCE/f-MWCNT@Mn2(Phen)4O­(Cl)2-Nf, phen = 1,10-phenanthroline), prepared by an in-situ electrochemical method using the precursor, Mn­(phen)2Cl2, as an efficient and low cost alternate to the Os-complex transducer, for the glucose oxidase enzyme (GOx) based bio-electro-catalytic system. The existence of the key active site, [Mn2III(phen)4(O)­(Cl)2]2+, on the modified electrode was confirmed by physicochemical characterizations using transmission electron microscope, Raman, infrared, and UV–vis spectroscopes and electrospray ionization mass spectrometry techniques. The Mn-complex modified electrode showed a redox peak at E°′ = 0.55 V vs Ag/AgCl in neutral solution with a surface excess (ΓMn) value of 5.6 × 10–9 mol cm–2. The GOx enzyme bioanode prepared by adsorbing GOx on the Mn-complex modified electrode has shown an efficient bioelectrocatalytic oxidation of glucose with a Tafel slope value of 111 mV dec–1. Amperometric it analysis of glucose showed a calibration plot in a linear range of 50–550 μM and with current sensitivity of 316.7 μA mM–1 cm–2. The current sensitivity value obtained here is about 2–80 000 times higher than that of the Os­(bpy)-complex based transducers used for GOx based bio-electro-catalytic applications. Utilizing this new bioanode system along with a Pt-based oxygen reduction electrode, a new biofuel cell was constructed and achieved a power density value 7.5 μW cm–2.