In nanofluidic electrochemical sensors based on redox cycling, zeptomole quantities of analyte molecules can be detected as redox-active molecules travel diffusively between two electrodes separated by a nanoscale gap. These sensors are employed to study the properties of multiferrocenylic compounds in nonpolar media, 2,3,4-triferrocenylthiophene and 2,5-diferrocenylthiophene, which display well-resolved electrochemically reversible one-electron transfer processes. Using stochastic analysis, we are able to determine, as a function of the oxidation states of a specific redox couple, the effective diffusion coefficient as well as the faradaic current generated per molecule, all in a straightforward experiment requiring only a mesoscopic amount of molecules in a femtoliter compartment. It was found that diffusive transport is reduced for higher oxidation states and that analytes yield very high currents per molecule of 15 fA.
Mathwig, K., Zafarani, H. R., Speck, J. M., Sarkar, S., Lang, H., Lemay, S. J. G., ... Schmidt, O. G. (2016). Potential-Dependent Stochastic Amperometry of Multiferrocenylthiophenes in an Electrochemical Nanogap Transducer. Journal of physical chemistry C, 120(40), 23262-23267. https://doi.org/10.1021/acs.jpcc.6b07320