Dollar Store Microfluidics!

“Anyone can make a microfluidic device at home with $4000 of equipment” has been ringing around in my head lately. I need to silence that voice. I need to silence it the only way I know how:

Dollar Store Microfluidics

So what are microfluidic devices? Elveflow has a pretty good explanation: "Microfluidics is both the science which studies the behaviour of fluids through micro-channels, and the technology of manufacturing microminiaturized devices containing chambers and tunnels through which fluids flow or are confined. Microfluidics deal with very small volumes of fluids, down to femtoliters (fL) which is a quadrillionth of a liter. Fluids behave very differently on the micrometric scale than they do in everyday life: these unique features are the key for new scientific experiments and innovations."

TL;DR fluids in sub-mm channels behave differently than fluids in channels above 1mm in diameter, and using these behaviors we can do a bunch of very cool science. For example: drug delivery through microdroplets, chemical assays using a fraction of the reagent you'd need for wet chemistry, particle sorting through inertial separation, etc.

1. Gel tape x2
2. Hobby Knife
3. Baby droppers
4. Small pump bottle (for the tubing)
5. Scissors
6. Magnifying sheets
7. Binder clips (to act as a stand)
8. Small containers
9. Water!

All told the materials and tools came out to $9. (No sales tax in NH!)

The rules are simple: every material and tool used must come from the dollar store with no exceptions. I had no idea if this would work but I was shocked at how possible it seemed as I went. I’ll break down the items I’m trying out by category: tools, fluid handling, chip material, and misc. I didn't really have a plan going in, and decided the best route as I went, so a lot of stuff didn't get used. I plan to make some more dollar store microfluidic stuff in the future, so be sure to comment if you see something in the supplies that gives you an idea!

Shockingly good selection at Dollar Tree. Only thing missing was a good pair of scissors and a not-holographic ruler. The $1 hack saw is amazing and hilarious and I hope it can at least cut plastic. The hobby knife and tweezer set were another nice surprise. The knife blades were super sharp, though they amusingly did not come with any sort of case or cover.

Not shown: scissors (very essential)

This is by far the hardest part, and so I bought a lot of different stuff to try. Of particular interest were those little pump spray bottles. That right there is some good silicon tubing if I ever done seen it. The tubing is super duper important in actually delivering the fluid into the chip, so that was clutch. The baby droppers, tubing, and a little hot glue made for a decent "poor mans syringe"

I figured that tape based microfluidics was probably going to be the most viable, but I got a few things to try out because hey, it’s only $1. I found some magnifying sheets that had a perfectly flat side and were easy to cut, and those will act as the base of the chip. The channels were constructed by carefully placing gel tape onto the plastic backing, then covering the channels and the tubing with more gel tape. The gel is super malleable and allows for you to "form" it around the tubing, creating a pretty solid seal.

Two parallel pieces of gel tape were carefully placed about .8mm away from one another. There's no real trick to this, you just have to have a steady hand and be careful. The tubing was inserted into the channels, and then a single piece of gel tape was placed over everything to form a good seal. in the picture you can see a little bit of leakage around the tubing, but that can be fixed by molding the gel around the tubes a little bit.

Cutting the gel tape can be a pain, all I can recommend is to use a very sharp knife (knapped obsidian if possible) and take small cuts, like they do in surgeries. This stuff is super sticky, but is honestly a great material to work with.

The baby dropper hole was widened a bit so that the tubing could be press fit inside it. A little bit of hot glue was added to the end to seal it. This worked VERY well considering it was all bought at a dollar store.

I wanted to do a little test run with a right angle bend to see what leaking may occur. Here you can see I used plastic sheet > gel tape > plastic sheet to construct the chip. After this I decided it would be better to go plastic sheet > gel tape > gel tape instead. The single straight channel shows the syrigne in action, as well as the new construction method.

With the basic construction techniques figured out, I placed some pieces of gel tape in such a way to form a T-junction (these are mostly used in droplet microfluidics), plumbed it up and BOOM pretty decent channels with only a little bit of leaking. Not too bad for ~$10 worth of equipment and materials! This could theoretically be connected up to a proper fluid pump and be used to generate droplets

The fab process for this final design is as follows:

1. Cut the base plate from the lens sheet
2. place down initial layer of tape to form channels
3. place tubing into channel
4. tape over the channels with more gel
5. squish around the tubing connections to provide a right fit
6. secure the baby droppers to tubing
7. input liquids

The major downside to this is the difficulty in cutting of the gel tape means that only simple geometry can be constructed; lines and right angles mostly. Either a different double sided tape would have to be used, or a better way to cut it worked out.As always the securing of the tubing to the syringe and to the channels was an issue. I’ve solved this in the past with custom printed Luer connectors. A possible solution here would be to use CA glue to secure the plastic bit that the tubing connects to in the bottle to the dropper, that way you have a nice secure connection to the tubing and don’t need to permanently bind the tubing and the droppers.

Fluid driving is also a pain, with the best bet here being gravity. Droplets could still possibly be formed using longer tubing and droppers held at differing heights. I’ve also seen some balloon based pressure driven systems that I’m probably going to try out with an actual chip. Overall this has been a really cool exercise in rethinking how I make chips and using what is available to get the job done. I was honestly amazed at the variety of item you could get at a dollar store, and once I picked up a pair of scissors the work flow was actually pretty solid.

I had never made a Side-Ported chip before which was kind of cool too. I had a few more ideas on possible fabrication methods too that I didn’t get to try out, like using that transparent film as a backing instead of the lens sheet in order to make a totally flexible chip.I know this has been a little all over the place so if you have any questions about specifics let me know! I think I’m stopping at this point and am going to switch gears to testing out some fluid driving mechanisms using the leftover dollar store stuff and an actual chip. Once that’s solid I’ll try to combine the two and then try out some