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Transparent Gold as a Platform for Adsorbed Protein Spectroelectrochemistry: Investigation of Cytochrome c and Azurin
journal contribution
posted on 2016-02-21, 16:02 authored by Idan Ashur, Olaf Schulz, Chelsea
L. McIntosh, Iddo Pinkas, Robert Ros, Anne K. JonesThe majority of protein spectroelectrochemical methods
utilize
a diffusing, chemical mediator to exchange electrons between the electrode
and the protein. In such methods, electrochemical potential control
is limited by mediator choice and its ability to interact with the
protein of interest. We report an approach for unmediated, protein
spectroelectrochemistry that overcomes this limitation by adsorbing
protein directly to thiol self-assembled monolayer (SAM) modified,
thin (10 nm), semitransparent gold. The viability of the method is
demonstrated with two diverse and important redox proteins: cytochrome c and azurin. Fast, reversible electrochemical signals comparable
to those previously reported for these proteins on ordinary disk gold
electrodes were observed. Although the quantity of protein in a submonolayer
adsorbed at an electrode is expected to be insufficient for detection
of UV–vis absorption bands based on bulk extinction coefficients,
excellent spectra were detected for each of the proteins in the adsorbed
state. Furthermore, AFM imaging confirmed that only a single layer
of protein was adsorbed to the electrode. We hypothesize that interaction
of the relatively broad gold surface plasmon with the proteins’
electronic transitions results in surface signal enhancement of the
molecular transitions of between 8 and 112 times, allowing detection
of the proteins at much lower than expected concentrations. Since
many other proteins are known to interact with gold SAMs and the technical
requirements for implementation of these experiments are simple, this
approach is expected to be very generally applicable to exploring
mechanisms of redox proteins and enzymes as well as development of
sensors and other redox protein based applications.