Thanks for your email! I will try to answer your questions as best I can.
On Sat, Mar 7, 2015 at 6:32 PM, Csaba Konrád csab...@gmail.com wrote:
I just found out about the project and I find it really fascinating!
I’m in a lab where we do very repetitive experiments on ALS patient
fibroblasts and I think the DropBot would be a great step forward.
I’ve built 3d printers in the past, soldered a little bit and can program
somewhat in python, so I should be able to build it as cheap as possible and
get a lot of functionality out of it.
I want to convince my boss, most of my questions were already answered here
but I still have a few:
Are chips reusable, or you throw them out all the time?
The time your chips last will depend a lot on how good your
fabrication process is and what you’re doing with the DMF chips. If
you’re moving liquids with a lot of proteins in them, they will tend
to foul over time and drop movement becomes increasingly difficult. If
you are moving protein-free liquids, devices can last a very long
time. Oil-filled devices will also last longer relative to those
operated in air.
There are also some tricks that can partially recover the function of
devices that have been fouled by proteins (e.g., reflowing Teflon by
heating your devices on a hot-plate).
Does teflon bind RNA/DNA from the droplets? This would be important for
example for PCR, where very little cross contamination can cause problems.
Personally, I don’t have a lot of experience in moving DNA/RNA, but
there are certainly many examples in the literature of people doing
PCR. My understanding is that moving DNA/RNA is less challenging as
compared to proteins since DNA/RNA are usually hydrophilic, which
means that they will have less of a tendency to stick to the
hydrophobic Teflon surface.
If you are interested in PCR, I think the bigger challenge is
preventing drop evaporation. Most of the people doing PCR on DMF use
an oil filler.
You mentioned the chromium plated glass and I saw the jove publication
Do you always make them, or is there a company that sells them? I think the
litography and the spin coating would be doable in our lab.
We used to chromium plate our own glass slides by e-beam, but now we
mainly purchase them from a company called Telic
(http://www.teliccompany.com/). That jove paper is quite old and our
fabrication methods have improved since then; it’s better to look at
any of our more recent publications for the latest procedures.
Also in the jove I don’t understand why the protein precicpitate stays in
place while the droplet moves away. I saw that the droplet is moved very
slow. Is this not a tricky step? Do you have to design it in a way that you
have a lot of precipitate? Did you ever try to precipitate DNA or RNA?
Proteins with hydrophobic domains will stick to the Teflon, which in
most cases is a bad thing because it impedes droplet movement, but in
this case it will help to anchor the precipitated proteins to the
surface. Moving a droplet over the surface produces very low shear
stress, which is probably why the proteins remain in place. I don’t
think that this step is particularly tricky. Nobody in our lab has
worked with precipitating DNA/RNA as far as I know…
When doing magnetic separation do you use an inductor to generate a field
controlled by the electronics or put a magnet under the chip?
We use a permanent magnet. See the following paper for details:
Choi, K.; Ng, A.H.C.; Fobel, R.; Chang-Yen, D.A.; Yarnell, L.E.;
Pearson, E.L.; Oleksak, C.M.; Fischer, A.T.; Luoma, R.P.; Robinson,
J.M.; Audet, J.; Wheeler, A.R. "Automated Digital Microfluidic
Platform for Magnetic-Particle-Based Immunoassays with Optimization by
Design of Experiments" Analytical Chemistry 2013, 85, 9638-9646.
(available on our website:
You mentioned somewhere that you are working on inkjet printable chips, is
it by AgIC(http://shop.agic.cc/collections/circuit-printer)? Do you spincoat
The inkjet printed devices are described in this paper:
Fobel, R.; Kirby, A.E.; Ng, A.H.C.; Farnood, R.R.; Wheeler, A.R.
“Paper Microfluidics Goes Digital” Adv. Mat. 2014, 26, 2838-2843.
(available on our website:
Can parts of the chip be heated (like not more than 100C) or do the droplets
The temperature limitation is mainly set by the dielectric. Parylene-C
is rated for a continuous service temperature of 80C and a short term
service temperature of 100C. We exceed this temperature during the
Teflon reflow step of our fabrication process, and it doesn’t result
in catastrophic failure, but exceeding 80C for extended periods of
time may damage your device over the long term (Parylene data sheet:
Evaporation will definitely be a problem if you plan to heat your
drops to anywhere close to 100C. You can ameliorate this problem
through drop replenishment and/or using an oil filler.
Hope that helps,
If there answers for these in your papers than sorry, don’t bother to answer
i still need to go through them.
Thank you and bests,
On Thursday, September 12, 2013 at 1:42:13 PM UTC-4, Ryan Fobel wrote:
Thanks for your email. These questions actually come up a lot, so it’s
great to get this info out there for everyone. You’ve nailed a really
big problem with DMF as it currently stands. I think that the DropBot
system makes it easy for anyone to build a DMF control system, but
unless you can get/make devices, it’s not incredibly useful. Our lab
has published lots of DIY-friendly, rapid prototyping techniques for
DMF devices (http://microfluidics.utoronto.ca/publications.php)
including micro-contact priting, PCB-based devices, dielectric films,
etc., but none of them are perfect, and certainly the devices made
using glass-substrate/photolithography have the best performance in my
We fabricate our own chips in the cleanroom facility at the University
of Toronto. Fabrication details can be found in any the publications
on our website (e.g.,
I am familiar with the cross-referencing scheme (I think this was
originally published by CJ Kim’s group several years back, before I
started). Some of the issues, if I remember correctly, were:
- electrode cells in the same row/column as the target will be at
- your software requires logic to avoid conflicts when actuating
multiple electrodes in parallel
- probably requires 2 HV amplifiers (180 degrees out of phase)
In any case, it would be possible to build a DropBot system that could
support cross-referenced devices without too much trouble. But if you
require two amplifiers, any cost savings from limiting the number of
switches may be negligible. I do think this is a promising scheme
though, especially because it would really allow your device
geometries to scale up.
I’m also familiar with some of the efforts to make low voltage
devices. I think this could be really important for reducing the cost
of the control electronics and would also have some other nice
benefits (safety, portable, battery-powered systems). Right now the
biggest expenses from the electronics side are the high-voltage
amplifier and the high-voltage solid state relays. If drops could be
manipulated with <20 V, the whole control system could be much
We’ve mostly been focused (so far) on improving device robustness and
reliability and not so much on these other issues. To reduce the
voltage, you need to either (a) increase the dielectric constant of
your insulating layer and/or (b) reduce the thickness of the
dielectric. Previous students in the Wheeler lab have experimented
with some alternative dielectrics (e.g., barium titanate, silicon
nitride) that have higher a dielectric constant, but with our
equipment, we can only coat devices in small batches (i.e., <4),
whereas using Parylene-C, we are able to coat >100 at a time. Also,
with thinner dielectrics, you can run into problems because it is more
common to get small imperfections. Any failure point in the
dielectric, will cause breakdown and electrolysis of your drop.
I’m planning to setup some kind of a wiki or blog on the DropBot
website so that we can organize some info on potential low-cost device
fabrication strategies, future development ideas, etc. Right now, I’m
mainly focused on writing hardware assembly documentation as well as
my other research papers so that I can eventually graduate
But it is a near term goal to at least be able to support people who
want to experiment with different device fabrication strategies. I
suspect that there are people out there in the community who can
figure out a great way to make cheap, reliable, and maybe even
On Thu, Sep 12, 2013 at 11:31 AM, Ryan George > > >> ryan...@knights.ucf.edu wrote:
I see everything besides the actual chip in the hardware list. Where can
this be purchased or made? I have a synthetic biology club that would be
interested in making a dropbot to use while working on the iGEM
I also wanted to know if you were familiar with DMF chips that had cross
referencing capabilities to open up the area you can work with quite a
There are also methods to get the voltage down to less than 15 volts:
I was wondering if you have already considered these technologies in
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