Switchable surface properties through the electrochemical or biocatalytic generation of Ag0 nanoclusters on monolayer-functionalized electrodes

The electroswitchable and the biocatalytic/electrochemical switchable interfacial properties of a Ag+-biphenyldithiol (BPDT) monolayer associated with a Au surface are described. Upon the application of a potential corresponding to -0.2 V the Ag+-BPDT is reduced to the Ag-0-BPDT interface, and silver nanoclusters are generated on the interface. The application of a potential that corresponds to 0.2 V reoxidizes the monolayer to the Ag+-BPDT monolayer. The reversible electrochemical transformation of the Ag+-BPDT monolayer and of the Ag-0-BPDT surface was followed by electrochemical means and surface plasmon resonance spectroscopy (SPR). The SPR experiments enabled us to follow the kinetics of nanoclustering of Ag-0 on the surface. The hydrophobic/hydrophilic properties of the surface are controlled by the electrochemically induced transformation of the interface between the Ag+-BPDT and Ag-0-BPDT states. The Ag-0-BPDT monolayer reveals enhanced hydrophilicity. The hydrophobic/hydrophilic properties of the interface were probed by contact angle measurements and force interactions with a hydrophobically-functionalized AFM tip. The Ag-0-BPDT interface was also biocatalytically generated using alkaline phosphatase, AlkPh, and p-aminophenyl phosphate as substrate. The biocatalytically generated p-aminophenol reduces Ag+ ions associated with the surface to Ag-0 nanoclusters. This enables the cyclic biocatalytic/electrochernical control of the surface properties of the modified electrode.