Fabrication of Flexible Polymer Tubes for Micro and Nanofluidic Applications

B. Ilic and H. G. Craighead

School of Applied and Engineering Physics and the Nanobiotechnology Center,

Cornell University, Ithaca, NY

Micro and nano-fluidic systems are being considered for chemical and biological analysis. Applications include: DNA and protein separation, drug delivery, biochemical reaction systems, liquid and gas chromatography, microfluidic mixing, electrophoresis and electroosmotic flow systems, and other complex fluid flow systems. Compact fluidic devices offer an increase in speed of analytical device operation while consuming low volumes of both samples and reagents.

In our work, we describe a fabrication method for forming self-sealing polymer tubes that can be either integrated into a previously formed device or formed as a flexible self supported polymeric system formed in a mold. The method involves lithographic definition and subsequent bulk etching to create templates in robust materials (e.g. silicon) into which polymeric flow channels are created. In our experiment we employ a room temperature vapor-phase deposition of a polymer to fabricate centimeter-long, self-sealing tubes with sub-micrometer lateral dimensions in either isotropically or anisotropically etched silicon molds (see Fig 1). Tubes are formed as the material pinches off during the deposition process to leave closed tubes or other volumes (see Figure 2). Once the tube is formed, access holes for fluidic interconnects can be created using standard lithographic processes and the resulting tubes are either removed from the mold or left integrated with preexisting devices. We demonstrated this process using physical vapor deposition of Parylene C, but the same process will work for other vapor deposited polymers. Parylene C is a suitable choice for the polymer material for a variety of applications because it is chemically inert and biocompatible. The biocompatibility suggests possible uses as artificial blood vessels and implantable fluidic networks. Additionally, the coatings have good electrical and physical properties and low permeability to corrosive gasses. Furthermore, Parylene is compatible with conventional microelectronic fabrication processes and has been used as an interlevel dielectric in complementary metal-oxide semiconductors.

Using fabricated 2 port fluidic networks, we demonstrated capillary flow of Flouroscene Isothiocyanate, AntiIgg, protein A and both capillary and electrophoretic flow of rhodamine B through the polymer tubes of up to 5cm in length. We tested the flow capabilities of the fabricated fluidic network by flowing various biochemical solutions through the channels. We demonstrated capillary flow, pressure driven flow and electrophoretic drive through the channels. Capillary flow was achieved by dispensing about 100ml of fluorescently labeled solution at the inlet port of the fluidic network positioned flat on a horizontal surface. The flow through the channel was observed using optical fluorescence. We show capillary flow of Flouroscene Isothiocyanate, and Rhodamine B solutions through the entire 5 cm length of the fabricated channels.

For electrophoretic drive experiments, a plastic tube that contains an integrated platinum wire was connected to the polymer tubes using a curable adhesive . A solution of 5X tris-borate EDTA buffer (Sigma T-7527) was first placed at the inlet and the outlet of the channels. 200ml of 0.1mg/ml Rhodamine B was dispensed into the inlet port. A DC potential of 160V was applied for 30min with the positive terminal at the inlet since Rhodamine B is slightly positively charged. We show that the dye is electrophoretically driven and had traversed the 5cm channel length and accumulated at the outlet.

Figure 1. Arrays of fabricated Parylene tubes inside (a) 40:1 aspect ratio, 10mm deep anisotropic and (b) isotropic silicon molds. Scale bar corresponds to 50mm. (c) Cross-sectional scanning electron micrograph (SEM) of a fabricated tube inside of an anis tropically etched silicon template. Scale bar corresponds to 5mm.

Figure 2. Non-conformal step coverage of the high aspect ratio deep trench caused by lack of surface adatom migration.

Publication Reference:

B. Ilic, D. Czaplewski, M. Zalalutdinov, B. Schmidt and H. G. Craighead, "Fabrication of Flexible Polymer Tubes for Micro and Nanofluidic Applications", Journal of Vacuum Science and Technology B, 20, 2459-2465 (2002).