Strategies to extend the lifetime of bioelectrochemical enzyme electrodes for biosensing and biofuel cell applications

Abstract

Enzymes are powerful catalysts for biosensor and biofuel cell electrodes due to their unique substrate specificity. This specificity is defined by the amino acid chain's complex three-dimensional structure based on non-covalent forces, being also responsible for the very limited enzyme lifetime of days to weeks. Many electrochemical applications, however, would benefit from lifetimes over months to years. This mini-review provides a critical overview of strategies and ideas dealing with the problem of short enzyme lifetime, which limits the overall lifetime of bioelectrochemical electrodes. The most common approaches aim to stabilize the enzyme itself. Various immobilization techniques have been used to reduce flexibility of the amino acid chain by introducing covalent or non-covalent binding forces to external molecules. The enzyme can also be stabilized using genetic engineering methods to increase the binding forces within the protein or by optimizing the environment in order to reduce destabilizing interactions. In contrast, renewing the inactivated catalyst decouples overall system lifetime from the limited enzyme lifetime and thereby promises theoretically unlimited electrode lifetimes. Active catalyst can be supplied by exchanging the electrolyte repeatedly. Alternatively, integrated microorganisms can display the enzymes on their surface or secrete them to the electrolyte, allowing unattended power supply for long-term applications.

Real-Time Monitoring of Cellular Bioenergetics with a Multianalyte Screen-Printed Electrode

“…29 Four common methods for achieving this aim are enzyme entrapment in a polymer, cross-linking, covalent attachment to the electrode, or microencapsulation within an electrode. 29–31 In the case of the glucose sensor with an 18 month lifetime, GOx was added to the carbon ink used to prepare the thick-film SPEs, which enabled extended sensor lifetimes. The sensors discussed in this study were stabilized by cross-linking with glutaraldehyde, which provides enough stability for lifetimes longer than a month when stored in buffer, but not enough to allow long-term, dry storage.…”

Probing the Electrocatalytic Oxygen Reduction Reaction Reactivity of Immobilized Multicopper Oxidase CueO

“…UV-Vis spectro-electrochemical experiments of CueO in phosphate buffer in the presence of 1 mM K 4 Fe(CN) 6 and 1 mM K 4 W(CN) 8 as redox mediators and employing a gold mesh working electrode (for details see experimental part and ref. 49 ) revealed a strong absorption band with a maximum at 610 nm ( Figure 5A).…”

“…[3][4][5][6][7][8] Key factors are (i) the interaction of the enzyme with the electrode surface, which may lead to denaturation, (ii) the orientation on the surface as well as (iii) the positioning of the active site of the enzyme such that it remains accessible for solution species. 9 Moreover, electroactive enzymes contain a redox active moiety that should remain close enough to the electrode surface to allow fast and effective redox communication.…”

Abiotic (Nonenzymatic) Implantable Biofuel Cells

“…This directly translates into high current densities at low polarization losses, and thus high electrical power densities. However, the drawback of enzymes is their limited long-term stability [5]. Their catalytic activity strongly depends on correct folding and formation of Table 14.…”

“…their three-dimensional protein structure, and through oxidation and the breaking of bonds enzymes tend to lose a significant share of their catalytic activity over time. While current research approaches thus try to stabilize the correct folding, for example, by the introduction of additional intramolecular bonds or the immobilization of enzymes in stabilizing polymer structures, most of these approaches only delay the natural degradation of enzymes [5]. So far, a maximum lifetime of up to 40 days has been realized in the context of implantable biofuel cells [6].…”