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PDMS vs. Glass - and the Winner is…

by on 15 April, 2013

We are often asked to compare microfluidic chips made out of glass versus PDMS.

This is an excellent request, as there certainly are some significant differences that should be taken into consideration when shopping for microfluidic devices. There is a consensus among microfluidic device users that chips fabricated with glass substrates represent the gold standard for many applications due to their dimensional stability, optical characteristics, chemical inertness and low auto-fluorescence. Keep in mind, though, that fabricating these devices out of fused silica requires complex hardware and is rather expensive.

In contrast, microfluidic chips can be created using rapid prototyping methods, such as Polydimethylsiloxane (PDMS) molding. PDMS is a viscoelastic polymeric compound that is commonly referred to as silicone (not to be confused with Silicon, a totally different material). PDMS is optically clear (but depending on the fabrication, it may include small air bubbles that scatter light), and, in general non-toxic and non-flammable. PDMS samplePDMS sample

While depending on your skill level and access to a chemistry lab, fabricating chips out of PDMS may be relatively inexpensive, there are serious drawbacks associated with PDMS. PDMS is a material that is mechanically soft, is prone to swelling and auto-fluoresces. Some will argue that the deformability of PDMS allows for the easy realization of leak-proof fluidic connections, but in our view, the negatives far outweigh the positives. The restricted chemical compatibility of PDMS prevents its use in many microfluidic applications. PDMS swells when in contact with many chemicals commonly used in laboratories [1] or it shrinks when the ambient humidity is low. Furthermore, small hydrophobic molecules readily partition into and out of bulk PDMS, complicating the determination of their on-chip concentration [2], and potentially invalidating measurements.

PDMS microchannels also experience elastic deformations under imposed flow rates. These deformations affect the flow profile and pressure distribution within the channels. Deformations have been demonstrated to be an important consideration in low aspect ratio (height to width) channels. The effect becomes increasingly pronounced for very shallow channels. [3]

For all of these reasons, we do not provide microfluidic devices made from PDMS and we strongly caution you about their shortcomings.

References:

  1. J. N. Lee, C. Park and G. M. Whitesides,” Solvent Compatibility of Poly(dimethylsiloxane)-Based Microfluidic Devices“, Anal. Chem, 75, pp. 6544–6554, (2003).
  2. M. W. Toepke and D. J. Beebe,”Shrinky-Dink microfluidics: 3D polystyrene chips”, Lab Chip, 6, pp. 1484–1486, (2006).
  3. Thomas Gervais, Jamil El-Ali, Axel Guntherb and Klavs F. Jensen, “Flow-induced deformation of shallow microfluidic channels”, Lab Chip, 6, pp. 500–507, (2006) DOI: 10.1039/b513524a
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