Protocols - SOPs
Poor-man’s 5-minute Elastomer gaskets
Poor man’s 5-minute Elastomer gaskets for single-molecule experiments (and more):
For many in vitro biomolecular studies, e.g., optical microscopy, nanopore experiments, AFM, etc, one requires containment of an aqueous sample of fluid. It is often convenient to have a moldable elastomer that is PDMS-like, but without having to wait for long time for the elastomer to fully cure before an experiment. Although such elastomers are commercially available, they are quite expensive (~$30-40 for a 4 ml tube). I will not even provide you with the link for this product (ask me if you really need it)! Instead, let me share with you a recipe I developed for a platinum-based silicone elastomer that fully cures within 3-5 minutes, suitable for single-molecule studies. The overall cost of this elastomer is <$1 per 4 ml, a factor of 40 less than the commercial one. Nevertheless, I warn you, the process is a bit creepy… you will need to order this from a company that makes fake body skin for theater and movies, so some pictures there are pretty horrible. So, if you have not eaten yet, go on:
A) Ecoflex 5 Pt Silicone Rubber Compound, 400 ml cartridge, 5 minute cure, net weight 1 lb. Cost: $36 (as of Sept 2010):
B) Silicone thinner: 1 pint of fluid. This lowers the mixed viscosity of silicone rubber. Net weight 1 lb. Cost: $11 (as of Sept 2010):
C) Pigments (OPTIONAL): You may want to add them so that you can verify proper mixing. I like blue (Silc Pig Blue – 4 oz.) and yellow (Silc Pig Yellow – 4 oz.), they make green when mixed They’re $17 a color, and last more than a lifetime:
D) Mini-dual syringe: These are 2ml+2ml two-chamber syringes for simultaneous 1:1 diepensing of each components (see product 4B19 in link). Get a hundred empty ones and keep them in the lab (<$1 each).
E) Other stuff you’ll need is a coarse balance, a plastic weighing dish, two mixing tools (one for each component, I use a pipette tip or a toothpick), and 2 30 ml syringes that have a 3″ long 1/8″ i.d. plastic tube attached to the luer. Also, you will need steady hands so you don’t mess up your lab bench. You WILL need paper towels.
1) Lay a paper towel on a coarse balance, and the weighing dish on top. Tare the balance. Label each cylinder of the Ecoflex 5 as A and B. Break the bottom seal, and squeeze out by pushing on one of the pistons component A directly into the weighing dish, until you reach 30 grams. When squeezing it out, make sure you tilt the tube such that when you squeeze out component A you don’t contaminate the outlet of component B.
2) Open the bottle of silicone thinner, and using a glass pipette, drip into the 30 grams of component A 1 gram of thinner.
3) (OPTIONAL) Open the blue pigment, and add a tiny amount of it using a pipette tip (equivalent to 1 drop or 10 microliters).
4) Mix the contents thoroughly using a toothpick or a pipette tip until you get one homogeneous blue mix. Set this mix aside.
5) In a different weighing dish, repeat steps 1-4 for Component B, the thinner, and the yellow pigment. Mix very thoroughly.
6) That’s it… or is it? OK, now is the fun part: you will need to inject one component into each chamber of the dual-syringe. One way is to fill two 30 ml syringes, each with one component mix, by pouring the contents into the syringe from the cylinder side (i.e., by removing the piston). Then, replace the piston and attach a 3″ long 1/8″ i.d. plastic tube to the luer lock via an adapter. Then squeeze out each component from the bottom all the way to the top of the dual-syringe without introducing bubbles. After filling both chambers, stick the dual-piston in and voila!
7) Typically a 30 gram preparation will yield 7-9 syringes, so you’ll need to do this every several months, or if you use it profusely, every month.
By pressing on the mini-syringe piston, squeeze out a similar volume of each component onto a flat surface (microscope slide). Mix thoroughly using a fine pipette tip (gel-loading tips work great). Then, use as needed by molding into any shape or drawing a circle onto the surface you wish to use. Within 3-5 minutes you will have a dry silicone rubber. Remember, this is not as optically transparent as PDMS, it is just a clean gasket for working with aqueous fluids.
The elastomer can typically be pulled off of a flat surface after it has cured. In addition, hexane makes it swell, which facilitates removal. However, if you need to dissolve it completely, you will need to get Dynasolve 210. This miracle solvent is based on a protic organic acid, and it dissolves regular PDMS as well. Use in hood.