Employing Heterocyclic Dihydropolyazines for Amperometric Glucose Sensing

Abstract

Glucose sensors containing heterocyclic dihydropolyazines: 5,10-dihydro-5,10-dimethylphenazine (DHDMP) or 1,4-dihydro-1,3,4,6-tetraphenyl-s-tetrazine (DHTPT) as mediators and glucose oxidase adsorbed on graphite rods generated an anodic current at 0.10 (DHDMP) and 0.55 (DHTPT) V vs SCE in the presence of glucose at pH 7. The potential of the sensors correlated with the electrochemical conversion of the mediators. Under aerobic conditions calibration graphs for the sensors showed a slightly sigmoidal character with half-saturation concentrations of 58 ± 6 and 43 ± 9 mM glucose and Hill coefficients of 1.68 ± 0.07 and 1.88 ± 0.16, respectively. The calibration curves were hyperbolic over the whole glucose concentration in deaerated buffer solution and the sensitivities were 0.47 and 0.18 μA/mM for DHDMP and DHTPT containing electrodes, respectively. The sensor response increased in weakly alkaline medium. Calculated values of pK_a, (7.0 ± 0.2), were similar for both type electrodes, were independent of buffer solution components and correlated with glucose oxidase reactivity (pK_a = 7.3 ± 0.05) in homogeneous solution. The sensors action was explained by formation of the radical cation of the dihydropolyazines, their action with reduced glucose oxidase and oxidation of the electrochemical mediators. The potential of the electrodes depended on the formal redox potential of the mediator, whereas current was a result of the radical cation reactivity and solubility.