Edge enriched self-assembly of Au nanoparticles: Coffee-ring effect during microcontact printing via agarose stamps

Amino functionalized surfaces were selectively modified via the combination of a wet agarose stamping technique and microcontact printing technique. Because of the specific reaction environments and diffusion of HNO2 confined in agarose stamp, the reaction of amino groups in the edge of the strip pattern was much more intense than other areas. The modified amino groups in the edge areas show higher affinity to Au-NPs than other areas, consequently, edge enriched Au-NPs patterns were observed after the self-assembly of Au-NPs. A "cylindrical droplet" model, in a manner analogous to "coffee-ring" effect, was proposed to describe the diffusion of HNO(2 )from the bulk to the edge in agarose stamp. By using such density varied Au-NPs patterns as templates for the growth of ZnO nanorods, we observed high density of Au-NPs resulting in high density and highly (0 0 1) oriented ZnO nanorods. In contrast, sparse and non-oriented ZnO nanorods were grew on low density of Au-NPs areas. Our findings might open new routes for the fabrication of gradient patterns and extend applications of Au-NPs patterns in surface enhanced Raman scattering and catalysis