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 Ag0−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 Ag0−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 Ag0 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 Ag0−BPDT states. The Ag0−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 Ag0−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 Ag0 nanoclusters. This enables the cyclic biocatalytic/electrochemical control of the surface properties of the modified electrode.