Glass etching to bridge micro- and nanofluidics.

In this study, a simple and economical fabrication technique bridging micro- and nanostructures is proposed. Glass molds with micro-nanostructures are fabricated by glass microlithography. The microlithography provides flexibility for structure design, and the glass etching contributes to transform the micro glass ridge to the nanoscale. Glass ridge structures with triangular cross sections are generated by undercutting, which coupled the isotropic character of glass and the shield effect of the top Cr layer upon HF etching. Further etching induced the height of the glass ridges to shrink from micro- to nanometres due to the edge effects. At the late etching stage, the geometrical change of the glass greatly slows down, which gives better control over the size of the glass ridge. By glass structure mold-copy, well repeatable, mechanically stable and tunable polydimethylsiloxane (PDMS) channels and cones are fabricated. Scanning electron microscopy (SEM) and laser interferometry (LI) are carried out to characterize the micro-nanostructures. To demonstrate their workability, sample preconcentration to a single nanochannel level is carried out.