Micropipette: Parts, Types, and Uses
A pipette is equipment ideal for pipetting or transferring liquid samples in the laboratory. Generally, glass or regular pipette can only transfer sample volume in a milliliter. For laboratories handling small volumes of samples (volumes in microliters), the ideal choice is a micropipette.
A micropipette is the laboratory equipment used for aspirating and dispensing small volumes (as small as 0.2 µl) of liquid. These are used in pharmaceutical, molecular, forensic, and diagnostic laboratories. It is of different types based on its principle (air and positive displacement), capacity (P20-P10,000), channels (single and multi), and working mechanics (manual and automatic).
Parts of Micropipette
- Plunger: The plunger is the topmost part of the micropipette. Pushing down the plunger helps in the aspiration and dispensation of the desired amount of liquids. It consists of two stops, the first stop is for aspiration and the second stop is for dispensation.
- Tip ejector button: A button beside the plunger helps in the ejection/removal of pipette tips without using hands.
- Volume adjustment knob: It is a knob attached to the plunger. Turning it helps in adjusting the desired volume in the adjustable volume micropipette. It cannot be turned/rotated in a fixed volume micropipette.
- Digital volume display window: It displays the volume that the micropipette can withdraw.
- Plastic shaft: A plastic shaft is a tube-like structure filled with air in an air displacement micropipette. Once you press the piston, some amount of air from the shaft releases, helping in the aspiration of liquid. In contrast, releasing the piston helps dispense liquid, and the air again fills up the shaft.
- Ejector arm: It is an extension of the tip ejector button. It puts pressure on the pipette cone once the ejector button is pressed.
- Tip cone: It is the place where the pipette tip is attached.
- Pipette tip: It is equipment made up of virgin polypropylene or molded plastics that come in direct contact with the liquid.
How to Use a Micropipette?
The correct way of using a micropipette affects its durability. The procedure for operating it is as follows:
- Select the right micropipette: Any micropipette has a fixed volume range. P1000 is an adjustable volume micropipette measuring liquid from 100 to 1000 µl. Likewise, P20 can aspirate fluid from 2 to 20 µl. So select the pipette based on the volume of liquid.
- Adjust pipette to the right volume: After choosing the correct pipette, adjust the micropipette to the desired volume with the help of a volume adjustment knob. Do not turn the knob above the range of the micropipette. It will damage the micropipette.
- Attach the pipette tip: Select the pipette tip based on micropipette use. Avoid touching the tip with your hands; instead, place the micropipette above the tip and press down to attach the tip to the tip cone. Make sure the tip is firmly attached to the micropipette.
- Aspiration of liquid: The plunger of the micropipette has two stops. For aspirating, press the plunger to the first stop and dip the end tip into the fluid to be aspirated. Release the plunger but make sure the tip is inside the liquid until the plunger regains its original position.
- Dispensation of liquid: Insert the tip into the container where you want to dispense the sample. Firstly, press the plunger to the first stop and pause. Then, press the plunger to the second stop to completely expel the liquid. Hold the plunger until you pull the tip entirely out of the tube to avoid re-aspiration.
- Removing tip: Firstly, place the micropipette above the disposing container. Then, press the tip ejector button to remove the tip. Avoid using your hands to remove the tip.
Types of Micropipettes
Micropipettes are classified on different basis. The basis for the classification of micropipettes are; the principle, the number of channels, pipetting mechanism, and volume.
Based on the Principle/Displacement Method
Air displacement micropipette
The piston is inside the pipette. There is an air cushion between liquid and piston. During aspirating liquid, the piston displaces an equal volume of air to the volume adjusted in the micropipette. The temperature and viscosity of the liquid greatly influence the precision of the air displacement micropipette. Likewise, calibration of the micropipette from time to time is also necessary.
Positive displacement micropipette
The piston is not inside the pipette shaft but inside the pipette tip. There is no air cushion between piston and liquid. The piston contacts the liquid directly, and no air is replaced during aspiration. No external factors like temperature and viscosity influence these kinds of pipettes due to the absence of the air cushion. It is also accurate for samples that are viscous and volatile sample.
Based on the Number of Channels
Only a shaft is present in a single channel micropipette that can transfer one liquid at a time. They are available in various capacities and provide excellent accuracy. The capacity available ranges from 0.2 to 10,000 µl.
Multiple shafts are present in a multichannel micropipette that can transfer various liquids simultaneously. Common multichannel micropipette has 8-12 channels, but 4, 6, 16, and 18 channels are also available. It is best for tests involving multiple wells like ELISA, DNA amplification tests, etc. The capacity of multichannel micropipettes ranges from 0.2 to 1200 µl.
Based on the Pipetting Mechanism
In the mechanical/manual micropipette, personnel has to apply pressure to press the plunger for aspiration and dispensation. The piston has a spring.
An electronic button replaces the mechanical plunger. It is also called an automated pipette and replaces manual labor. These have customizable programs to adjust to any requirement of the pipetting.
Based on the Volume
Fixed volume micropipette
These do not have an adjustment knob for chaining the volumes. These pipettes transfer an equal volume of samples every time. It is ideal for transferring viscous liquids in laboratories with a limited budget. It decreases the chance of error due to mistakenly changing the volume.
Adjustable volume micropipette
These have volume adjusting knobs for changing the volume. The volume of these pipettes comes in a range like P20 can transfer a volume of 0.2 to 20 µl. The available volume ranges are as follows:
1000 µl= 1 ml
10000 µl= 10 ml
Uses of Micropipette
Micropipettes are suitable in the laboratory that handles minute (0.1 to 1000 µl) volumes of samples. Some areas that use micropipettes are as follows:
- Clinical and microbiological laboratory: It is used for different tests used in diagnosing diseases. Serological tests (antibody/antigen detection using rapid test kits, ELISA tests, etc.), molecular tests (sequencing, PCR, blotting techniques, electrophoresis, etc.), and virus culture in cell lines use it for transferring reagents/samples.
- Chemical laboratory: These laboratories use micropipettes to handle viscous and volatile liquids for various experiments.
- Forensic laboratory: These laboratories use micropipettes to analyze blood, tissues, and fibers. Micropipettes are also helpful tests that determine the genetics of victims or analysis of DNA materials and fingerprints found at the crime scene.
- Pharmaceutical laboratory: These laboratories use micropipettes for medicine/drug production. These also use micropipettes for the produced drugs’ QC (quality control) testing.
- Food and beverage industry: Primarily, micropipettes function as liquid handling devices in these industries, and quality assurance tests are another area of micropipettes’ application.
- Picus®: A single-channel or multi-channel electronic pipette. News-Medical.net. Retrieved 19 July 2022, from https://www.news-medical.net/Picus-A-single-channel-or-multi-channel-electronic-pipette.
- Electronic Pipettes | INTEGRA. INTEGRA. Retrieved 19 July 2022, from https://www.integra-biosciences.com/global/en/electronic-pipettes.
- Adjustable volume pipettes 0.5 to 10 µl. Sigmaaldrich.com. Retrieved 19 July 2022, from https://www.sigmaaldrich.com/NP/en/search/adjustable-volume-pipettes-0.5-to-10-ul.
- 1.3: Micropipetting. Biology LibreTexts. (2021). Retrieved 19 July 2022, from https://bio.libretexts.org/Bookshelves/Biotechnology/.
Ashma ShresthaHello, I am Ashma Shrestha. I am currently pursuing my Master's Degree in Microbiology. Passionate about writing and blogging. Key interest in virology and molecular biology
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