We demonstrate that scanning electrochemical microscopy (SECM) can be used to determine the conductivity of nanoparticle assemblies as a function of assembly potential. In contrast to conventional electron transport measurements, this method is unique in that electrical connection to the film is not required. The electrochemical potential of the assembly is set through the Nernst equation by the redox mediator present in solution in analogy to the gate electrode in traditional three-terminal transport experiments. In this proof-of-concept report, we show that the conductance of an assembly of small gold nanocrystals (NCs), so-called monolayer-protected clusters (MPCs), is strongly dependent on the electrochemical potential. This is due to the sub-attofarad capacitance of the MPC cores that gives rise to single-electron charging effects at room temperature
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