Hi, that's my first post on this forum 
I'm a scientist and I would like to design something special to help me in my experiments. I often use microplates in my researches Microplate - Wikipedia, but for now, I fill them by hand with micropipettes. And it's very time consuming. I would like to know if there is a way to dispense very accurate and small volumes in the wells. I mean, small like 10 µL, with an error range of 2-5 %.
Do you have an idea ?
Thanks anyway
Hi, welcome to the forum.
I suppose you control the plunger of a small syringe with a stepper motor to move it in very small amounts. Standard stepper motors can move as little as 1.8 degrees per step (200 steps per rotation), and that can be geared down to result in a smaller movement.
If the syringe was used inverted and the liquid forced out of a tube ending higher than the reservoir of the syringe you would eliminate any siphoning.
Sounds good. I'll just have to calibrate the syringe first and it would be ok.
I have a question however. I'll have a drop at the end of my tube, will it fall correctly and repeatably into the well ? Because I have to insist on the precision of the volume.
Like you say, have to calibrate the syringe first. I don't know, haven't done any Chemistry since fall of 1979 in college. Might have to play with tube diamater to find small enough size that won't support surface friction of a drop, and gravity will ensure it falls?
Ok, thanks for your answer, I'll for sure envisage it. What do you think about peristaltic pump, or selenoid pump ? I heard a lot about them, since I did a bit of digging.
I have no knowledge of them.
Ok. Of course I still accept other answers, especially about the pumps. I'm still not at the point where I build..
I wonder if you couldn't use something like Adafruit's peristaltic pump:
...substituting the DC motor used with something a bit more controllable? The pump as-is is rated at 100 mL per minute (about 1.67 mL per second - which is still waaay too high) - but maybe you can find a manufacturer of bare peristaltic pumps that makes one with a small range?
The motor on the pump above is supposed to be a 5000 RPM motor - so in one second it turn approximately 83 rotations; it uses a tri-wheel design, so that means in one rotation it pumps out 3 "squirts" - so 250 squirts in one second.
So - 1.67 mL divided by 250 = 0.0067 mL per "squirt" = 6.68 uL
I think I have that right? If so - then if you got one of these pumps, and hooked up a stepper motor to it, and stepped it just the right amount - it would pump the amount you are looking for (and no idea whether it would be in your error range).
Yep - lot's of if's - but seems possible...? Assuming my calcs were all correct...lol.
I wonder what people have in mind when they use the word "syringe". The sort I am familiar with have rubber pistons and require quite a lot of force to move them. I would be very surprised if that technology could dispense tiny quantities accurately. I think you would need a long-stroke, small diameter syringe with a ceramic or metal piston ground to extreme;y fine tolerances.
It occurs to me that it may be possible to get a small standard syringe with a small diameter needle to produce consistent sized drops while the piston is moved slowly and continuously. (A motor with a screw mechanism should be suitable). It should not be too difficult in a laboratory to check the consistency and size of the drops. Then it may be possible to use an optical detector to count the drops and, perhaps, to have a device (like a small rainwater gutter) that could be moved under the drops to catch extra ones after the desired number have fallen.
...R
What I have in mind about syringe is something like this:
They are syringe of 1 mL, and it's quite easy to move the piston. A motor with a screw mechanism (slow and accurate) could deliver the right amount of liquid. For the end of the tube, I was thinking about pipette tips
http://spellboundlabs.co.za/index.php?main_page=product_info&cPath=65&products_id=106
I have some which are low binding, so the liquid should not stick to the tip and fall into the well.
Off an a tangent: the specs for inkjet printers specify the size of the droplets in picolitres. Dunno how it works but it's a much smaller volume than you need and maybe the way those drops are produced can be adapted to your situation.
Pete
I thought inkets used heat to sort of burst the ink droplets out.
Yeah, could be. I've never looked into it but they are dispensing stuff several orders of magnitude smaller than the OP requires and maybe there's something useful there. Or not
inkjets can work with different ways but they all have a chamber (very small reservoir) that can be contracted by
There is a valve between the big reservoir and the chamber.
It is like squeezing a plastic bottle and when the bottle "reset"s its shape the valve opens and the chamber fills again
heat is used e.g. for wax , it melts and when it touches the paper it cools rapidly and stick to the paper.
piezo is used e.g. with more watery ink. One of the neat tricks with piezo is that one can squeeze the chamber and "unsqueeze" it almost instantly. The netto effect is that big part of the droplet is pulled back into the chamber resulting in an even smaller droplet. (it is patented )
cr0sh:
If so - then if you got one of these pumps, and hooked up a stepper motor to it, and stepped it just the right amount - it would pump the amount you are looking for (and no idea whether it would be in your error range).
That would be my suggestion is well, but I don't know where you can find peristaltic pumps driven by stepper motors and at a reasonable price. Any leads there?
We used these valves for a similar application. They are a bit expensive but do work well.
Good luck.
INKX0521850AA3.pdf (104 KB)
Okay thanks, but I haven't been able to find this model on the manufacturer site.
My advice would be to look at what machines which do automated pathology tests do.
I suspect that they use a very small peristaltic pump which squeezes out a predictable and repeatable amount of fluid for each turn or partial turn of the rotor.
In the chemistry labs at the university I went to, we had volume adjustable micropipette attachments for large stock bottle of certain chemicals.
Screw into bottle, set volume, push button. Very easy to attach a linear actuator or similar to repeatedly drive it. Probably quite easy to add something to automatically vary the volume.
Since you're already hacking, this at least has the hard/precise bits already assembled for you.
Maybe I understand you wrong, but I need to dispense MICRO liters, not MILLI liters.