Multiscale Fabrications

Nanofludic channels offer new opportunities for biotechnology and medicine, including separation of biomolecules, drug delivery, and single molecule detection because they provide unique capability. In addition to various applications, nanofluidic channel can be an ideal, well-controlled experimental platform to study nanoscale molecular, fluidic, or ionic transport properties. However, the fabrication of nanofluidic channels aligned with microfluidic networks currently requires precise lithography and nanofabrication procedures. To address the need for a simple, low-cost fabrication method for forming close-packed nanofluidic channels, we explore various approaches; a) Advanced conventional MEMS methods: fabrication process for planar nanochannel system and thermal oxide growth process for vertical nanochannel system; b) Non-lithographical methods: junction gap breakdown, wrinkles, surface patterning, and self-sealed nanoporous junctions.

A hybrid micro-/nanofluidic device which contains an array of parallel nanochannels has been employed to study polyelectrolyte multilayer (PEM) deposition in confined geometries. Layer-by-layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) at pH 4 and salt concentrations ranging from 0.1 to 1 M was used to conformally coat the nanochannel walls, systematically narrowing the channel width from 222 to 11 nm in the wet state. The thicknesses of confined multilayers were measured using SEM and these results were compared with those obtained on planar, unconfined surfaces. A procedure for direct measurement of the gap thickness using dc conductance was also developed. LbL assembly in the nanochannels resulted in lower bilayer thicknesses than those obtained on planar surfaces. This observation is attributed to the surface charge-induced depletion of unadsorbed polyelectrolytes within the channel. The ability to conformally coat the walls of the nanochannels with functional PEMs opens up new possibilities in the design of active nanochannel devices.

We develop a novel fabrication strategy for generating massively-parallel, regular vertical nanochannel membranes with a uniform, well-controlled gap size of ~50 nm and a depth up to ~40 µm, by using only standard semiconductor fabrication techniques. A continuous-flow separation of large DNAs and small molecules is demonstrated with large open volume, enabling high-throughput applications.