Micropipettes

Pipettes dispensing 1–1,000 µL are often called micropipettes. Different styles of micropipettes are designed to optimize working with certain types of liquids and can maximize productivity and healthy ergonomics. Micropipette styles include air- and positive-displacement manual and electronic pipettes, which can appear in both single- and multichannel formats and benchtop high-throughput platforms. All are designed to precisely aspirate and dispense microliter measurements of liquids.  

In both air-displacement and positive-displacement micropipettes, the diameter of the piston and the length of the piston stroke determine the volume of liquid that is aspirated and dispensed.

We use micropipettes to accurately transfer small volumes of liquid from one vessel to another. For example, we use a micropipette to move liquid from a cell culture flask to individual wells in a microwell plate. Micropipettes are used in environmental science, chemistry, pharmaceutical development, forensic science, biology labs, and many other areas.

Many micropipettes have very good accuracy specifications. These instruments have the potential to deliver volumes with very low systematic and random error. However, the technique of the micropipette user can greatly affect accuracy. Proper volume-setting, pipette tip pre-rinsing and tip immersion depth, as well as pipetting verticality and pipetting rhythm, can all influence reproducibility.  

Micropipettes are precision instruments that often undergo heavy use in the lab, so – in addition to good specs and proper technique – the most accurate micropipette is one that is regularly calibrated. Service intervals typically reflect the amount a micropipette is used.

To use a micropipette, first set and lock the volume. Next, lower the liquid-end of the micropipette into a clean, empty pipette tip. Make sure the pipette tip is securely mounted to the micropipette for an airtight seal. Once a pipette tip is loaded, on a manual micropipette, press the plunger down to the first stop. On electronic models, once volume is set and a tip is loaded, it’s ready to aspirate.  

Holding the micropipette vertically, immerse the tip into the liquid at the proper depth for the tip size. Immersing a tip too deeply increases pressure and may overfill the tip; immersing it too shallowly risks the aspiration of air.  

On a manual micropipette, slowly release pressure on the plunger to aspirate the set volume of liquid. On an electronic version, press the button to aspirate.

With liquid inside the tip, move the micropipette over the target vessel. On manual micropipettes, press the plunger to the first stop to dispense. On an electronic micropipette, simply press the dispense button.  

Finally, to clear any remaining liquid, move the micropipette over a desired discard vessel and, on manual micropipettes, press the plunger to the second “blowout” stop. On electronic micropipettes use the button to blow out any residual liquid.

To minimize the potential for error when working with a micropipette, start with a complete system of a micropipette and tip to ensure the proper airtight fit.  

Keep the micropipette as vertical as possible while working. On manual micropipettes, set the volume by dialing the micrometer slightly above the intended volume. Then, lower it to the desired number. Each time you load a new tip, pre-rinse it to optimize conditions within the tip for highly accurate pipetting. As you aspirate and dispense, keep your speed consistent, maintaining a rhythm throughout a protocol step.  

Dispensing below the target-liquid surface when possible or touching off – wiping the tip on the inner wall of the vessel as you complete your dispense – are both ways to maximize the accuracy of the volume you’re dispensing.

Different people refer to the same types of instruments both ways: some call them pipettes and others call them micropipettes. Popular usage has brought these terms together to refer to the same instruments, although micropipettes can be more narrowly defined as instruments capable of microinjecting fluid directly into cells. Pipettes, a broader term, encompass instruments ranging from eye droppers and mouth-operated tubes to serological pipettes and high-throughput pipetting systems.

Micropipettes are pipettes capable of measuring and dispensing liquid solutions in the volume range of 1 µL to 1,000 µL. They are commonly used in life science-related research where the accurate measurement and dispensing of solutions is required.