Effect of individual plasma components on the performance of a glucose enzyme electrode based on redox polymer mediation of a flavin adenine dinucleotide-dependent glucose dehydrogenase

Abstract

The performance of glucose enzyme electrodes, consisting of crosslinked flavin adenine dinucleotide glucose dehydrogenase (FADGDH), an osmium redox polymer and multi-walled carbon nanotubes on graphite electrodes, was tested in phosphate buffered saline, artificial plasma and the individual components of artificial plasma to assess the effect of each component on current response and operational stability of the response to better understand the decrease in electrode performance observed in blood. Electrodes tested in artificial plasma show a significant decrease in current response in 5 mM glucose, and operational stability of the response in 100 mM glucose, compared to electrodes tested in buffer. The lowest current response for the enzyme electrodes was observed in the presence of physiological level of uric acid although the largest alteration to enzyme affinity, as estimated from the apparent Michaelis-Menten constant, occurred upon addition of physiological level of sodium bicarbonate. The operational stability observed in the presence of uric acid was the lowest of all components tested, with only 46% of initial current response after 12 h, and was comparable to the 27% of current remaining after 12 h for electrodes operating in artificial plasma. The effect of uric acid on glucose oxidation by enzyme electrodes prepared using both glucose oxidase (GOx) and a recombinant cellobiose dehydrogenase (CDH) was assessed. The maximum current decreased for both FADGDH and GOx enzyme electrodes in the presence of uric acid, with no significant change to the enzyme affinity, suggesting non-competitive inhibition. The CDH based electrodes provided highest stability of current signal in buffer, with 86% of the initial signal present after 12 h, but display significant change in enzyme affinity, maximum current and operational stability, dropping to only 33%, in the presence of uric acid. In contrast the operational stability of the GOx-based enzyme electrodes was unaffected by the presence of physiological level of uric acid. As uric acid and sodium bicarbonate are present in blood, these results highlight the importance of enzyme selection for in vivo biosensing and biofuel cell applications. Further work is required to understand the mechanism of uric acid inhibition on each of the enzymes. (C) 2019 Elsevier Ltd. All rights reserved.