Microfluidic etching driven by capillary forces for rapid prototyping of gold structures

Soft lithographic methods based on poly(dimethylsiloxane) (PDMS) for pattern transfer are established alternatives to conventional lithographic methods. For applications in the biological sciences functionalized and structured noble metal surfaces are required. In order to allow for rapid prototyping of such gold structures a method is needed that does not change the surface chemistry. This can be achieved by a microfluidic system on a gold substrate that is filled with an etchant. From theoretical considerations simple thumb rules for the geometric and chemical design of such a micro fluidic system were established. For experimental testing a microfluidic system was realized by contacting a structured PDMS stamp with a substrate consisting of a 50-nm-thick gold layer on a glass object slide. The etchant was applied to the entrance of the capillary and the acid was drawn into the fluidic system by capillary forces. Taking advantage of a PDMS stamp structured wetting and non-wetting regions no additional self-assembled monolayer was needed for masking.