Nanochannels fabricated in polydimethylsiloxane using sacrificial electrospun polyethylene oxide nanofibers

 

Leon Bellan and Elizabeth Strychalski

School of Applied and Engineering Physics, Cornell University

 

 

We have used electrospun polyethylene oxide (PEO) nanofibers as sacrificial templates to form nanofluidic channels in polydimethylsiloxane (PDMS).  By depositing fibers on silicon templates incorporating larger structures, we demonstrate that these nanochannels can be integrated easily with microfluidics.  We use fluorescence microscopy to image channels filled with dye solution.  The utility of the hybrid micro- and nanofluidic PDMS structures for single molecule observation and manipulation was demonstrated by introducing single molecules of λ DNA into the channels.  This nanofabrication technique allows the simple construction of integrated micro- and nanofluidic PDMS structures without lithographic nanofabrication techniques.

 

Using sacrificial electrospun polyethylene oxide (PEO) fibers, we have formed nanofluidic channels in polydimethylsiloxane (PDMS).  Electrospinning is the process of forming nanofibers from a polymer solution using an electrically forced fluid jet.1  These fibers can be used as lithographic masks2-4 or sacrificial structures5 to form nanoscale features in other materials.  In this work, electrospun fibers were deposited onto a silicon chip, and PDMS was poured on top and allowed to cure.  The PEO fibers were removed from the cured PDMS by soaking the material in water, leaving nanochannels (process outline in Figure 1).  We demonstrated that these nanochannels can be easily integrated with standard microfluidics by depositing fibers on patterned silicon chips.  Imaging the channel cross-sections using a scanning electron microscope revealed the channels to have sub-micron diameters (Figure 2).  To ensure that the channels were open, we filled them with fluorescent dye and imaged the filled channels.  Figure 3 shows images of filled devices consisting of random and aligned channels.  We also introduced single molecules of λ DNA into the channels, demonstrating the utility of these integrated micro- and nanofluidic structures for single molecule observation and manipulation.  The paths of several isolated molecules of DNA are shown in Figure 4.  

 

Using this nanofabrication technique, it is possible to fabricate hybrid micro- and nanofluidic PDMS structures without using expensive and time-consuming conventional nanofabrication techniques.  These fluidic structures could be used for several purposes, ranging from separating and analyzing biomolecules6 to forming materials with artificial vascular structure.7  Of the materials used to form microfluidic structures, PDMS remains one of the most popular due to its versatility and ease of use.  Similarly, PEO is one of the most popular materials to electrospin because it is easy to work with, water soluble, and non-toxic. A fabrication process that combines these two materials is advantageous because the materials systems involved are well characterized and commonly used. Moreover, it should be straightforward to scale up this fabrication process to allow high throughput formation of micro- and nanoscale devices, rendering several applications previously confined to the research lab potentially commercially viable.

 

Figure 1- Process outline

 

 

 

Figure 2 -  SEM image of nanochannel cross section

 

 

 

Figure 3- Fluorescence microscopy image of channels filled with dye

 

 

 

 

Figure 4 - Fluorescence microscopy image of paths traveled by fluorescently labeled DNA molecules

 

 

 

References:

1              Reneker, D. H., and Chun, I.; "Nanometre diameter fibres of polymer, produced by electrospinning", Nanotechnology 7, 216 (1996).

2              Czaplewski, D., Kameoka, J., and Craighead, H. G.; "Nonlithographic approach to nanostructure fabrication using a scanned electrospinning source", J. Vac. Sci. Technol., B 21, 2994 (2003).

3              Czaplewski, D. A., Verbridge, S. S., Kameoka, J., and Craighead, H. G.; "Nanomechanical oscillators fabricated using polymeric nanofiber templates", Nano Lett. 4, 437 (2004).

4              Verbridge, S. S., Parpia, J. M., Reichenbach, R. B., Bellan, L. M., and Craighead, H. G.; "High quality factor resonance at room temperature with nanostrings under high tensile stress", J. Appl. Phys. 99, 124304 (2006).

5              Czaplewski, D. A., Kameoka, J., Mathers, R., Coates, G. W., and Craighead, H. G.; "Nanofluidic channels with elliptical cross sections formed using a nonlithographic process", Appl. Phys. Lett. 83, 4836 (2003).

6              Eijkel, J. C. T., and van den Berg, A.; "Nanofluidics: what is it and what can we expect from it?" Microfluidics and Nanofluidics 1, 249 (2005).

7              Toohey, K. S., Sottos, N. R., Lewis, J. A., Moore, J. S., and White, S. R.; "Self-healing materials with microvascular networks", Nature Materials 6, 581 (2007).