microINJECTOR™ All-Digital Multi-pressure System

MINJ-D:  $3,237.84

Power Options

Computer Connectivity

Needle Holder


For demanding applications that require a full-featured microinjection system, Tritech Research offers the MINJ-D All-Digital Multi-Pressure microINJECTOR™. In basic microinjection, a hollow needle with a microscopic tip is filled with a liquid, poked into a target, and then temporarily pressurized so as to inject some of the liquid into the target. The variables that determine the amount injected are pressure, time, viscosity of the liquid, and diameter of the needle opening. A simple, practical system for accomplishing this is our MINJ-1 microINJECTOR™ (standard model). While the MINJ-1, and its line of accessories, help many scientists breeze through their microinjections, some experiments and procedures require a higher level of sophistication, accuracy, and reproducibility. In basic microinjection, the needle is either at a user-set pressure when injecting, or at atmospheric pressure when not injecting. In some cases, backflow of cytoplasm or medium into the needle can be problematic. For these cases, a lower "holding pressure" that is lower than the injecting pressure, but higher than atmospheric pressure is useful between injections. A holding pressure can also reduce needle clogging. No matter how careful a person is, needles occasionally do clog. For these cases, a short blast of a "clearing pressure," higher than the normal injection pressure, is useful to unclog the needles. The MINJ-D employs a user-friendly microprocessor to digitally synthesize injecting, holding and clearing pressures, as well as injection durations reproducibly. Using a simple "Menu" button, and Up and Down buttons, anyone can set the pressures and the injection duration in seconds. It's so intuitive, you won't have to read the directions! Here are the key features and specifications of the Digital microINJECTOR™:
  • Most compact on the market
    6" x 7" x 3" and weighs under 2 lbs.
    (15cm x 17cm x 7cm and weighs under 1 kg)
  • Fast response time between pressures (~100 milliseconds)
  • Simple 3-button control
  • Digital display with backlight for easy reading
  • Microprocessor accuracy
  • Foot pedal included for hands-free injection control
  • Pressure range (applies to each of holding, injecting and clearing pressures): 0 - 100 psi
  • Programmable Injection Duration: 0.1 - 999.0 seconds
  • Built-in Vacuum Generator can be used to front-fill needles by aspiration
  • Manual Injection Mode
  • Injection Data-logging Port for optional computer interface
  • Injection Control Port for optional computer control

The MINJ-D can be attached directly to a laboratory compressed air jet or attached to a compressed Nitrogen cylinder using a pressure regulator such as our TREG-N2.  The system is designed to use a minimum of gas, so even a small cylinder may last for months or years. When ordering, please let us know if you intend to attach your injector to a compressed gas source or an in-house air jet, so that we can provide you with the proper fittings for attachment.

The output of the microINJECTOR needs to be coupled to something. For example, if you're using glass microcapillary needles, our MINJ-4 microINJECTOR™ Brass Straight-Arm Needle Holder will do the job cost-effectively.

A special version, the MINJ-4FEM, is designed for those that prefer to use Eppendorf® prepulled Femtotips® (that screw on) instead of our own lower-cost MINJ-PP prepulled needles that are compatible with our standard MINJ-4.

Another special version, the MINJ-4SLIP, is designed for those who prefer to use SlipTip® and Luer-Lok® Needles (that push or twist on) instead of our MINJ-PP glass needles.


Q: What is the pressure resolution of the microINJECTOR™?
A: The MINJ-D is capable of pressure control in increments of 1 psi or 1 kPa (6.9 kPa = 1 psi), depending on which unit mode you choose... So you get almost 7 times more resolution in kPa mode!

Q: How much input pressure should be supplied to the MINJ-D via my regulator when using a lab air jet or nitrogen tank as a pressure source?
A: First, never exceed 80 psi (550 kPa), or you may damage the unit or create an unsafe situation!

For the best control, you should set the regulator just a little higher than the highest pressure that you need to deliver. You could start with 50 psi (345 kPa) input and then use the menus to find the best injection pressure (and possibly a clearing pressure that is higher than the normal injection pressure). If you find, for example, that your useful pressures are all under 20 psi (140 kPa), and that the unit is overshooting or not hitting/maintaining the pressures as consistently as you would like, then you can lower the input pressure to 25 psi (175 kPa), and it will be more stable at lower pressures.

Q: Can I still use the MINJ-D with my laboratory compressed air jet or compressor if it delivers greater than 80 psi (550 kPa)?
A: The MINJ-D requires input pressure between 10 psi (70 kPa) and 80 psi (550 kPa); it must be at least the pressure you need to deliver, but not more than 80 psi. If your lab air jet or compressor might ever deliver pressure above 80 psi, you can use a low-pressure regulator with quick-connects at the input and output ports to reduce and stabilize the input pressure. You can order these from us, so contact us to order the correct model. Please note that opening an air jet port only slightly or restricting the flow does not lower the pressure in a closed system, it only slows down how long it takes to get to the full pressure; a pressure regulator is needed to lower the pressure.

Q: How can I prevent material from flowing out through the tip of the needle even when the foot pedal is not depressed?
A: If material is flowing out of the needle between injection pulses, this indicates excessive Holding Pressure. You can either set the Holding Pressure to zero, or set it more precisely. If you are having trouble finding a Holding Pressure menu setting where nothing is coming out of the needle, and you are in PSI mode, you might want to start by switching the unit to kPa mode by using the Units menu. This will increase the pressure resolution by nearly a factor of 7. If that still doesn't achieve the holding pressure you'd like, then select the Holding Pressure where it is slightly too high (some solution is still coming out of the needle) then turn the vacuum control knob (on the right hand side of MINJ-D) slowly counter-clockwise (from its original closed and fully-clockwise position) until no more solution is flowing out of your needle tip. The vacuum control knob adjusts the system from injecting-mode (all the way clockwise) to vacuum-mode (all the way counter-clockwise). By turning the knob slightly counter-clockwise, you are reducing the pressure slowly until you find the balanced pressure where there is no material flowing out of your needle tip. With appropriate Holding Pressure, there should be minimal flow out of the needle between injections.

Q: I am trying to inject zebrafish/xenopus eggs and not getting good control. What settings or procedures should I use?
A: Make the needle tip opening as small as possible. Having a smaller needle tip will increase your accuracy when injecting with the MINJ-D because it will let you use higher pressures to get the desired volume injected. We recommend using the procedure of etching the needle tip in HF acid to open the needle tip so that it is sharper and creates a smaller opening than just breaking it off with an exacto knife or tweezers. We have a protocol for this in the FAQ section of our MINJ-PP product page.

By injecting some dye into a petri dish of water, and you can experiment with setting the pressure to make sure that the Holding and Injecting pressures are set appropriately so that there is minimal backflow of water or outflow of dye with your needle, without wasting any of your actual sample. You can also switch the unit to kPA mode instead of psi mode, and you will get nearly 7 times more precision. You can also lower input pressure to a bit higher than the actual pressure at which you are injecting. This way, the MINJ-D will be able to regulate the pressure more precisely. For example, if your injecting pressure is at 2 psi (14 kPa) but your input/source is at 80 psi (550 kPa), each time you press the foot pedal, your injection may overshoot because the inrushing input pressure is so much higher than your injection pressure; however, if your injecting pressure is reduced to 5 psi (35 kPa), there will be less overshoot.

Q: How do I connect the tubing to my Nitrogen regulator?
A: If you purchased the TREG-N2 N2 regulator from Tritech Research, it should have a brightly colored "quick-connect" fitting in its output, and the MINJ-D tubing should lock right into it. The way that the quick-connect works is: to lock in the tube, you insert the tube in as far as it will go (you will feel resistance and overcome it) and when you slowly try to pull out the tube, you will then feel it lock into place; to remove the tube, hold in the brightly colored ring of the quick-connect fitting while pulling out the tube.

Q: What procedure would you recommend to stop everything between injections to avoid turning on and off the system multiple times?
A: Turning the system off does not vent the holding pressure. Instead, it will vent when you turn it back on. In between injections, to cancel an ongoing injection or deactivate the Holding Pressure, we recommend using the Minus Button (-), which activates the Abort function. It will stop the current pulse, if any, and it will also vent the Holding Pressure.

Q: How can I reset the system to factory settings?
A: To reset the device to factory settings:
1) make sure power is turned off
2) hold down the plus (+) button
3) while continuing to hold down the (+) button, turn on power to the device
4) after text appears on the display, release the (+) button

Q: How can I load the specimen manually from the back?
A: In most microinjection applications, the total volume for all the injections is less than 1 microliter, and the tip is too small to suck up anything meaningful, so you can preload the needle from the back before you put it in the needle holder. This can either be done by capillary action, if the amount needed is well less than 1 microliter and the pipets have an internal glass filament, or they can be filled from the back by drawing a glass tube very finely with a flame or by using commercially available loading pipets (each of which are fine enough to fit inside the OD of the capillary tube).

Q: Is there a maximum vacuum pressure that the MINJ-D is able to apply?
A: The theoretical maximum vacuum for the unit, if you have the injecting pressure set to 60 psi with an input pressure of 80 psi (the maximum allowable) and the vacuum control valve wide open and a needle in the needle holder is: -86kPa = -12.5 psi = -.85 atm. Which isn't bad considering a perfect vacuum is 1 atm. Under more normal settings and realistically, it would be about half of that.

Q: For Xenopus egg injections,
- What is the ideal injection pressure?
- What is the ideal holding pressure?
- What is the ideal clearing pressure?
- What is the ideal injection interval?
A: The answer to all of the ideal settings above will be highly dependent on the needle tip opening. We suggest an extremely fine tip in the 1 micron range. In that case, you might inject at 10 psi for 1 second and have a holding pressure of maybe 2 psi and a clearing pressure of 30 psi.
However, some labs use much more open needles, and the pressures need to be much lower. We recommend the acid etching technique described on our MINJ-PP page in the FAQ section at the bottom to get very sharp needles.
The vacuum pressure control is the very small gray knob on the right side of the MINJ-D box. For normal injection, it should be screwed in all the way (clockwise). For a strong vacuum, it should be unscrewed until you hear maximum flow. For fine control of the holding pressure, it should be unscrewed minimally to prevent flow out of the needle tip when a low holding pressure is set.

Q: Is it possible to deliver brief injections (e.g. 100us) every 1s by keeping the foot pedal pressed?
A: The short answer is no. The MINJ-D has a minimum injection time of 100ms (0.1 secs). Even if the valve could switch at speeds in the microsecond range (its minimum switching time is about 10ms, as achieved in our MINJ-FLY) I don't think that it would be meaningful because it would take much longer than that for the air in the tubing and needle holder and pipette to pressurize and depressurize.
We have a version of the MINJ-D with a computer interface that would allow it to give repeated pulses, for example every second. The important variable is to get your needle tips to the right opening size such that 100nl comes out at a pressure setting of several psi in less than 0.5 secs. Then you will have good control.

Q: How can I transition from using a laboratory air jet to a Nitrogen tank as the pressure source for a micro injector, such as the MINJ-D?
A: All you have to do is unplug the MINJ-D's input tube from the little regulator and plug it directly into the bigger cylinder regulator. You unplug it by holding in the yellow ring while pulling out the tube. You lock the tube into this kind of fitting by pushing it all the way in and slowing pretending to pull it out while NOT holding in the ring, and the fitting will bite into the tubing. On the cylinder regulator (which is not "self-relieving") the chrome purge valve, pointing toward the bottom, should normally be closed. But, if you need to lower the set pressure, you have to open it a little bit so that the pressure has somewhere to go as you turn the big white pressure knob counter-clockwise- since the injector and needle holder is basically a closed system. Then close the valve after the new, lower pressure is set. Also use the purge valve when finished with an injection session:
1) close cylinder valve
2) open purge valve to drain all pressure (without reducing pressure using the white knob)
3) optionally lower potential pressure by turning white knob counter-clockwise until "looser" for increased safety.
For normal use, turn the white knob clockwise so that the output gauge on the cylinder regulator shows the same input pressure for the MINJ-D that the user liked before with the in-line regulator.

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