Iron–sulfur-based single molecular wires for enhancing charge transport in enzyme-based bioelectronic systems

Abstract

When redox enzymes are wired to electrodes outside a living cell (ex vivo), their ability to produce a sufficiently powerful electrical current diminishes significantly due to the thermodynamic and kinetic limitations associated with the wiring systems. Therefore, we are yet to harness the full potential of redox enzymes for the development of self-powering bioelectronics devices (such as sensors and fuel cells). Interestingly, nature uses iron-sulfur complexes ([Fe-S]), to circumvent these issues in vivo. Yet, we have not been able to utilize [Fe-S]-based chains ex vivo, primarily due to their instability in aqueous media. Here, a simple technique to attach iron (II) sulfide (FeS) to a gold surface in ethanol media and then complete the attachment of the enzyme in aqueous media is reported. Cyclic voltammetry and spectroscopy techniques confirmed the concatenation of FeS and glycerol-dehydrogenase/nicotinamide-adenine-dinucleotide (GlDH-NAD(+)) apoenzyme-coenzyme molecular wiring system on the base gold electrode. The resultant FeS-based enzyme electrode reached an open circuit voltage closer to its standard potential under a wide range of glycerol concentrations (0.001-1M). When probed under constant potential conditions, the FeS-based electrode was able to amplify current by over 10 fold as compared to electrodes fabricated with the conventional pyrroloquinoline quinone-based composite molecular wiring system. These improvements in current/voltage responses open up a wide range of possibilities for fabricating self-powering, bio-electronic devices.

Inorganic iron-sulfur clusters enhance electron transport when used for wiring the NAD-glucose dehydrogenase based redox system

“…Cyclic voltammetry of ferricyanide/ferrocyanide redox couple (Fe(CN) 6 3−/4− ) has been previously utilized to verify the formation of self-assembled monolayers (SAMs) on electrode surfaces [15, 22]. In this study, the formation of individual SAMs on gold electrodes was verified using cyclic voltammograms (CVs) obtained by applying a potential sweep on the electrodes placed in potassium ferricyanide solution.…”

“…Previously, we reported ability of inorganic iron(II) sulfide (FeS) to anchor nicotinamide adenine dinucleotide-dependent glycerol dehydrogenase (NAD + -GlDH) to the gold electrode surface [15]. This work was inspired due to the electron mediating role of iron-sulfur clusters in the biological electron transport chain(s) [16] and the reported performance of iron-sulfur protein derivatives for bioelectrochemical applications [17–20].…”

“…This work was inspired due to the electron mediating role of iron-sulfur clusters in the biological electron transport chain(s) [16] and the reported performance of iron-sulfur protein derivatives for bioelectrochemical applications [17–20]. The FeS-based electrode assembled during our preliminary work displayed promising electrical charge transport properties, likely, as a result of reduced internal resistance of the enzymatic electrode caused by the shorter FeS single-molecular-wires; and the ability of FeS to be a single-molecular anchor as well as an electron shuttling agent between nicotinamide adenine dinucleotide (NAD + ) coenzyme and the solid electrode support [15, 21]. Although the ability of FeS to anchor and enhance electron transport in the NAD + -GlDH model system was elucidated in our previous work, there is still a gap in knowledge with regard to the utility and performance of other inorganic iron-sulfur compounds for anchoring biomedically relevant redox enzymes such as glucose dehydrogenase.…”

Integrated Approach of Agri-nanotechnology: Challenges and Future Trends

“…Additionally, nanotechnology based devices are also used for plant breeding and genetic engineering purposes (Jiang et al, 2013). The encouraging development of nanotechnological approaches in agriculture particularly for crop productivity and disease management is shown by current trends of publications and patents (Ghormade et al, 2011; Kah and Hofmann, 2014; Mishra et al, 2014b; Parisi et al, 2015; Mishra and Singh, 2016). To date, several studies have addressed how nanotechnological approach is benefiting the agricultural sector in number of ways.…”

“…However, despite the exciting results obtained by involvement of ground-breaking nanotechnology in agriculture so far, their relevance have not yet reached up to the market. This is mainly attributed to small scale bench-top researches, ambiguous technical benefits, insufficient economic interest, biosafety concerns, regulatory issues and public opinion (Parisi et al, 2015). Additionally, the hovering apprehensions about fate, transport, bioavailability and toxicity of nanoparticles, limit the complete acceptance and willingness to adopt nanotechnology in agricultural sector.…”