Identifying multi layers or direction of flow with colored dots using Elmer’s Glue (polyvinyl acetate) and food coloring

Penny Burke and Teresa Porri
Cornell Nanobiotechnology Center, Cornell University, Ithaca, NY, USA

Why is this useful?

When making devices that are direction-specific and very small, you need to check them in the microscope each time to see which side to start your flow.  With this technique you can mark the PDMS with a color marker that does not interfere with the device.  When working with a multilayer device that has multiple valves and channels it is convenient to have identification markers.

What do I need?

  • PDMS
  • Elmer’s Glue (polyvinyl acetate)
  • Food coloring
  • Applicator stick
  • 1ml syringe
  • 27ga blunt tip needle

What do I do?

  1. Put 2-3 ml of Elmer’s Glue in a small container and mix 1-3 drops of food coloring, depending on how bright you want the color to be. Mix a large enough amount of colored glue so that you can draw it up into the syringe without adding bubbles.  Larger volumes are easier to draw into the syringe.
  2. Express some of the glue out of the syringe so that you do not introduce any bubbles into the PDMS.
  3. Mix PDMS in the usual 10:1 ratio and pour over your wafer, checking for bubbles.
  4. Gently insert the syringe needle into the PDMS and inject a small amount of glue. Injected glue tends to stay where it is injected (Fig. 1).
  5. Carefully remove the syringe from the PDMS.
  6. Cure the PDMS as normal (Fig. 2).
Image of colored glue injected into PDMS

Fig.1: Injected glue tends to stay where it is injected

Cured PDMS

Fig. 2: Cure the PDMS as normal

What else should I know?

An applicator stick may be used instead of a syringe. Also, this procedure will work on top of the PDMS, but it will change its surface.

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