3D nanomolding for lab-on-a-chip applications.

The ability to decorate microfluidic channel walls with additional micro/nanostructures becomes important as a means to modify the flow behavior, such as mixing and pressure drop, as well as to enhance the reactivity of bio-reactions to the surface in lab-on-a-chip applications. Despite the ability of mass production at low cost, conventional micro and nanomolding techniques are limited to the patterning of planar or slightly curved polymer substrates. Here we show a two-step molding technique, named 3D nanomolding, which allows the patterning of arbitrarily hierarchical multiscale structures, even nanostructures formed on the vertical sidewalls of microfluidic channels. In the first molding step, an ultra-thin intermediate polydimethyl siloxane (PDMS) stamp is produced by spin-coating and curing PDMS prepolymer on a pre-nanopatterned poly(methyl methacrylate) (PMMA) substrate, which is followed by the second molding step using the primary PDMS stamp containing microstructures. Various hierarchical micro and nanostructures are demonstrated, which include a biomimetic superhydrophobic structure in a lotus leaf surface to modify the surface wetting property and microfluidic channels where the walls are patterned with nanostructures. Despite the presence of nanostructures on the top surface, 3D nanomolded microchannels could be sealed well with a nanopatterned PMMA cover plate using solvent bonding to form enclosed microfluidic devices. The results indicate that the 3D nanomolding technique is suitable for decorating microchannel walls for lab-on-a-chip applications.