Surface Modification of a Self-Assembled Ferredoxin Monolayer on a Gold Substrate by CHAPS

A self-assembled ferredoxin monolayer on a gold substrate was prepared, and surface modification to remove the protein aggregates was performed with a zwitterionic surfactant, (3-[(3-cholamidopropyl) dimethylammoniol-1-propanesulfonate) (CHAPS). It was found that CHAPS segregates most of the ferredoxin aggregates nonspecifically adsorbed on the substrate. The atomic force microscopy image of the self-assembled ferredoxin monolayer taken from the substrate with CHAPS treatment shows that the size of the ferredoxin clusters is about 10-20 nm, which is on the order of clusters of 2-3 ferredoxin molecules. On the other hand, the size of ferredoxin aggregates without CHAPS treatment was measured to be about 100 nm. The current-voltage relationship of the self-assembled ferredoxin monolayer with CHAPS treatment was confirmed to remain intact by means of cyclic voltammetry measurements. Those results demonstrate that the elimination of the protein aggregates nonspecifically adsorbed on an inorganic surface is possible without losing the electrochemical property of protein molecules and thus this technique would be useful to improve the long-term stability of biomolecular electronic devices.