Improved operational stability of mediated glucose enzyme electrodes for operation in human physiological solutions

Stability of glucose-oxidising enzyme electrodes is affected by substances in physiological solutions, hampering deployment as long-term implantable biosensors or fuel cells. The performance of Nafion over-coated enzyme electrodes, consisting of multiwalled carbon nanotubes and flavin adenine dinucleotide-dependent glucose dehydrogenase (FADGDH) or glucose oxidase (GOx) crosslinked with osmium-complex based redox polymer, was compared to uncoated electrodes in presence of uric acid and artificial plasma. Nafion over-coating resulted in lower glucose oxidation current densities compared to no over-coating. The highest initial current density for Nafion over-coated electrodes in artificial plasma in 100 mM glucose was 8.0 ± 2.0 mA cm^-2 for GOx electrodes with 0.5% w/v Nafion coating. These electrodes retained 83% of initial current after 12 h continuous operation in artificial plasma while similarly prepared FADGDH electrodes retained 58% signal. This is compared to retention of only 73% or 31% observed for GOx or FADGDH electrodes in artificial plasma with no Nafion membrane. Enzyme electrodes over-coated with Nafion maintain improved signal stability when tested continuously in the presence of uric acid, identified as being the main contributing substance to FADGDH enzyme electrode instability, showing promise for application to continuous use glucose-oxidising enzyme electrodes.