[DIYbio] Re: NeverWet Spray-on superhydrophobic coat for "mini"-fluidics

Hello
Others mentioned Rain-x too. I used Rain-x as it was written as a published protocol in Lab On A Chip journal.  (That journal might also be called the "'We'll publish near anything as long as it's slightly mentionable in Wired' Journal".)   Deep in the supplementary notes for a few microfluidics experiments are references to Rain-X.   Gee, wonder why that wasn't part of the abstract?  Are postdocs afraid of mentioning a common auto-parts store product as the core of their experimental results?  8-D   Certainly the P.I.'s jaw hit the floor when I finally mentioned what coating worked best in my experiments (I also tried some polymer thin films which didn't work as well).

Anyway,
The basic idea is to drop/spray/spin some quantity of Rain-x on glass or whatever surface you like.  I used FR4 printed circuit board since I was doing electrowetting experiments which had copper traces pre-etched on the boards.  Then you bake the coated substrate at a certain time & temp.  I used my kitchen oven.  It worked to some degree (no pun intended).  Pics on my blog http://88proof.com/synthetic_biology/blog/archives/tag/microfluidics

Another alternative (also in the publications) is to paint saran-wrap (a good & cheap film-over-substrate) with the coating of choice.  You can cut out the patterns of saran-wrap ahead of time with your desired channel pattern (positive image), paint them, then carefully place the film on your substrate, then bake at temp.  The saran wrap will melt to the substrate at the right temp.  I think doing a negative image as a resist for the coating would be really tough, or doing the paint-then-cut-out, like you describe, would also be tough.

Maybe you could try putting the coating liquid (i.e. rain-x) in an inkjet printer head and spraying it on your substrate (i.e. print out the desired positive of the channel image).  Not sure if the nanoparticle stuff would print through an inkjet printer or not.  Rain-x might spray but it also might clog the inkjet heads too.


As you suggest, once the coating gets chemically dirty, the substrate becomes sticky and the chip is toast.  But you might try an emulsion on top of the substrate, i.e. do your experiment in water-in-oil; then the substrate is coated & washed in oil so it's more likely to remain usable for longer.  Then the "is the coating compatible?" question may be less important.   I thought I heard that the nano coatings fail in the presence of salts (maybe that's hearsay, just something I remember from somewhere, or maybe a lot of washing is required).  One problem I encountered (with the electrowetting) was arcing due to high voltage, somewhat due to imperfections in the chips or for whatever reason, which would leave deposits on the chips thus destroy the coating.

What would be interesting now, since 3D printers have reached good enough resolution (sub-0.5mm), is to print chips-with-fluid-channels on demand, clean them, spray them with the hydrophobic coating, then use.  By coating the channels, or maybe only certain channels, the flow of the reagents might get interesting (better mixing?  or control flows across certain temp zones?).  If you find a compatible plastic to print with, then running the chips through the dishwasher then an autoclave step then recoat might recycle them a few times.

--     ## Jonathan Cline  ## jcline@ieee.org  ## Mobile: +1-805-617-0223  ########################    

On Friday, December 20, 2013 1:35:54 PM UTC-8, Luis Zaman wrote:

 I picked up some "Rustoleum NeverWet" from the local hardware store and sprayed it on a few microscope slides to see what I could do with it.