# Off-the-shelf micro fluid dispenser

Need a way to dispense micro liter amounts of water (lets say 1-10ul). Only thing I've found is piezoelectric dispensers and they are >$100. Any suggestions? I can build, but preferably would be an off-the-shelf component. • Piezoelectric dispensers may be expensive, but they certainly count as "off-the-shelf". Are you asking how to build one for less than$100? Otherwise, this is a bit offtopic as a shopping question.
– Ian
Aug 8 '13 at 13:28
• I think he's looking for an alternative technology.
– jzx
Aug 9 '13 at 20:55
• Right, was asking for alternatives, like I know you could use a solenoid and a pump, but I don't know if it's feasible at that resolution. Was hoping someone with more experience could give me a hint at alternatives. Aug 10 '13 at 1:22

It may be practical to adapt some ink-jet printer heads to dispense water.

An ink-jet printer head projects a stream of droplets. Droplet volume varies widely among printers; typically, it's smaller in newer printers. Eg, a fairly-comprehensive 1998 inkjet tutorial at imaging.org says early HP 800-series ink-jets produced 6000 drops per second with 32 pL per drop, which works out to about 5.2 seconds to deliver 1 µL of ink. (I don't know if the DPS is per nozzle or per head.) The later 890C with a 192-nozzle head produced 12000 drops per second with 10 pL per drop, or about 8.3 s to deliver 1 µL of ink. As noted in a 2010 computerworld.com blog, the “Photosmart 8250 uses 3,900 nozzles to deliver 122 million drops per second onto the paper.”

(Note, with a drop-on-demand printhead, you could count drops – that is, control the number of pulses – vs turning the head on for a timed interval.)

An article called Non-Contact Liquid Handling: Basics and Technologies at labautopedia.org gives a good introduction to several techniques now in use for delivering small amounts of liquid. [Edit, May 2015: Article is gone; instead see Small Volume Pipetting and perhaps Microfluidic Sample Transport.] Among other topics it covers physics of droplet formation and illustrates several valving techniques.

Another useful survey, “Dispensing systems for miniaturized diagnostics”, is at ivdtechnology.com. [Edit, May 2015: Website is gone; perhaps see a search for related articles at mddionline.com]

The wikipedia inkjet article referenced earlier and a wikipedia microdispensing article are helpful but seem superficial compared to the imaging.org and labautopedia.org articles. Also see an nlm.nih.gov article about dispensing an enzyme-conjugated solution into an ELISA plate by adapting ink-jet printers, by Lonini et al.

I have used small solenoid valves with a fixed displacement to dispense small droplets. For example, the valve I used consistently pumped 0.5 uL from one orifice to the other every time it was switched. That particular valve was not intended to be used as a pump, but there was no reason it couldn't be. There are other solenoids which are intended to be used that way.

The valve I used costs less than $100. Unfortunately I can't share the specific part number, but you should be able to find some help from The Lee Company, or SMC, who sell these types of valves. Lee will definitely sell small quantities. I don't know about SMC. Either one should be able to provide you with samples. If your goal is to dispense a single reagent (water), then you are best off using a microdispensing valve based solution. I do not know that you will find something for less than$100, but if you went that route, you would be looking for parts like this.

There are other technologies out there (syringe based, capillary action based, pipette based), but none are suited as well as a microdispensing valve for bulk reagent dispensing in the 1-10uL volume range. You can find more technical information about microdispensing here.

Just how precise do you need to be? We build medical instruments and a \$100 pump would be considered pretty damn cheap around here. The most common technology is a syringe pump controlled by a stepper motor, but for precise, very repeatable dispense, fluid dynamic effects have to be considered. e.g., wicking off the droplet at the probe tip can have a dramatic impact on accuracy.