Mechanistic Control of the Growth of Three-Dimensional Gold Sensors

Three-dimensional (3D) electrodes with large surface areas are highly effective biomolecular sensors. These structures can be generated via the electrodeposition of gold inside microscale apertures patterned on the surface of a microelectronic chip. Such electrodes enable the ultrasensitive analysis of nucleic acids, proteins, and small molecules. Since the performance of these electrodes is directly related to their surface area, the ability to control their microscale morphology is critical. Here, we explore an electrochemical model based on the theory of nucleation and growth to better understand how to control the morphology of these electrodes. The insights gained from this model enabled us to create preferential conditions for the formation of different morphological features. We demonstrate for the first time that electrodeposition of 3D nanostructured microelectrodes inside a microscale aperture is governed by two stages of nucleation and growth. The first stage involves the creation of primary nuclei at the bottom of the aperture. The second stage features the generation of new nuclei upon exposure to the bulk solution. Depending on the overpotential, the deposition is then continued by either rapid growth of the original nuclei or fast growth of new nuclei. Faster electrodeposition at high overpotentials promotes directional growth, generating spiky structures. More isotropic growth is observed with low overpotentials, generating rounder features. Ultimately we determine the efficiency of DNA hybridization on a variety of structures and identify the optimal morphologies for rapid DNA–DNA duplex formation.