Ionic strength induced local electrodeposition of ZnO nanoparticles

The controlled maskless deposition of nanomaterials locally on surfaces is challenging and of relevance to numerous fields and applications, such as sensing and catalysis. Forming patterns of pre-synthesized, and therefore, well-defined NPs should become a general and simple building approach for manipulating surfaces. Electrochemical deposition of NPs under mild potentials is not common and is based on destabilizing nanomaterial dispersions by an electrical field. This approach that is termed from “nano to nano” is used here for the local deposition of ZnO NPs. Specifically, we employ scanning electrochemical microscopy (SECM) as a means of increasing locally the ionic strength by generating a flux of AuCl₄⁻ in a ZnO nanoparticle dispersion. The gold ions bind instantaneously to the ZnO NPs and drive their local deposition on a biased indium tin oxide (ITO) surface to form ZnO nanoparticle patterns embedded in Au. The ratio between Au and ZnO can be changed by controlling the AuCl₄⁻ flux at the SECM tip and the ITO potential. The as-electrodeposited ZnO NPs are characterized by microscopy and spectroscopy. Furthermore, the micron-sized Au-ZnO patterns are used as recyclable surface-enhanced Raman scattering (SERS) active substrates for the sensitive detection of a dye. The latter is only an example of the potential of such local nanomaterial-based patterns that can be readily formed by our approach.