Gold interdigitated nanoelectrodes as a sensitive analytical tool for selective detection of electroactive species via redox cycling

Redox cycling (RC) is a unique electrochemical technique to selectively detect redox-active species in presence of molecules with similar oxidation potential but whose electrochemical reactions display different electron transfer kinetics. Pairs of interdigitated electrodes (IDEs) working as generator-collector devices have been widely applied in RC. The diffusion of species that takes place between the two IDEs has to be minimized in order to enhance the device sensitivity. Therefore, scaling down the IDE dimensions is carried out to detect very low concentrations of the molecules under study. The application of interdigitated nanoelectrode structures (nano-IDEs) is currently limited by low-yield production and packaging processes. Here, we describe a fabrication approach that enables robust mass production of gold nano-IDEs at wafer scale, along with a packaging strategy to easily operate with the electrodes. The theoretical and experimental detection of dopamine in presence of ascorbic acid demonstrates the superior analytical performance of the resulting devices. Nano-IDEs with dimensions of 150 nm width and 300 nm pitch showed faradaic steady-state currents related to the oxidation of dopamine that were 16.7 times larger than those recorded by standard cyclic voltammetry. By contrast, if the dimensions of the nano-IDEs are increased by a factor of 10, the amplification factor of the redox reaction is decreased to less than one fourth.