Transient conformation changes of albumin adsorbed on gold piezoelectrodes

The adsorption of bovine serum albumin (BSA) on Au piezoelectrodes was investigated using Electrochemical Quartz Crystal Nanobalance (EQCN), redox ion probe, and tapping-mode AFM techniques. The high ionic conductance of Au|BSA films, owing to the presence of voids, allowed for extensive studies of the templated deposition of cadmium and electrocatalytic nitrate reduction processes. Changes in BSA conformation in the adsorbed state were found to occur on completion of Cd-upd formation in the presence of nitrate ions. The conformational transition was reversible and BSA film integrity was preserved, as confirmed in multiple scan experiments and by carrying out Quartz Crystal Immittance (QCI) measurements. No change in the resonance admittance modulus versus frequency was observed. We have found that triggering of BSA conformational transition is not associated with bulk-Cd0 nucleation and growth. Mechanistic considerations have led to the conclusion that BSA conformation changes are due to BSA adjustment to the changing electric field distribution in Au|BSA film associated with formation of surface complexes of partially charged Cd-upd with NO2− changing electrode charge and local pH increase caused by the electrocatalytic nitrate ion reduction. This mechanism is corroborated by the fact that in other Cd(II) solutions, not containing NO2− anions, conformational transitions in Au|BSA films were not observed.