posted on 2022-01-20, 15:33authored byVivek
M. Badiani, Samuel J. Cobb, Andreas Wagner, Ana Rita Oliveira, Sónia Zacarias, Inês A. C. Pereira, Erwin Reisner
The immobilization of redox enzymes
on electrodes enables the efficient
and selective electrocatalysis of useful reactions such as the reversible
interconversion of dihydrogen (H2) to protons (H+) and formate to carbon dioxide (CO2) with hydrogenase
(H2ase) and formate dehydrogenase (FDH), respectively.
However, their immobilization on electrodes to produce electroactive
protein films for direct electron transfer (DET) at the protein–electrode
interface is not well understood, and the reasons for their activity
loss remain vague, limiting their performance often to hour timescales.
Here, we report the immobilization of [NiFeSe]-H2ase and
[W]-FDH from Desulfovibrio vulgaris Hildenborough on a range of charged and neutral self-assembled monolayer
(SAM)-modified gold electrodes with varying hydrogen bond (H-bond)
donor capabilities. The key factors dominating the activity and stability
of the immobilized enzymes are determined using protein film voltammetry
(PFV), chronoamperometry (CA), and electrochemical quartz crystal
microbalance (E-QCM) analysis. Electrostatic and H-bonding interactions
are resolved, with electrostatic interactions responsible for enzyme
orientation while enzyme desorption is strongly limited when H-bonding
is present at the enzyme–electrode interface. Conversely, enzyme
stability is drastically reduced in the absence of H-bonding, and
desorptive enzyme loss is confirmed as the main reason for activity
decay by E-QCM during CA. This study provides insights into the possible
reasons for the reduced activity of immobilized redox enzymes and
the role of film loss, particularly H-bonding, in stabilizing bioelectrode
performance, promoting avenues for future improvements in bioelectrocatalysis.