What is a Micropipette?
- A micropipette is a laboratory instrument designed to measure and transfer very small volumes of liquid (in microliters, µL) accurately and precisely.
- Essential for experiments in molecular biology, microbiology, biochemistry, and pharmaceutical sciences.
- Unlike traditional pipettes that handle milliliters, micropipettes work in the microliter range (1 µL = 1/1000 mL).
- Provides high accuracy, repeatability, and contamination-free liquid transfer.
In short: A micropipette is the most reliable tool for handling tiny liquid samples in research and diagnostics.
History of Micropipette
- Early labs used glass capillary tubes for liquid transfer, but they were fragile and inaccurate.
- In 1957, Heinrich Schnitger (University of Marburg, Germany) invented the first micropipette.
- In 1960, Dr. Warren Gilson developed the piston-based adjustable micropipette (Gilson Pipetman), which became the standard.
- Since then, modern micropipettes have evolved with ergonomic design, accuracy, and electronic versions.
Parts of a Micropipette
All micropipettes share some common parts:
- Plunger Button – Used for aspirating and dispensing liquids; has two stops (first stop for aspiration, second stop for complete dispensing).
- Volume Adjustment Knob/Plunger Dial – Allows selection of required volume (in variable micropipettes).
- Volume Display Window – Shows the set volume in µL.
- Tip Ejector Button – Ejects disposable tips safely.
- Shaft/Barrel – Hollow tube where air displacement occurs.
- Disposable Tips – Attached to the shaft; used to collect and transfer samples.
- Ejector Arm – Removes tips without manual contact, preventing contamination.
*Using sterile, high-quality tips ensures accuracy and avoids contamination.
Principle of Micropipette Working
- Micropipettes work on the principle of air displacement (for most types).
- Pressing the plunger creates air pressure that moves liquid in or out of the tip.
- When plunger is released, a vacuum is created, drawing liquid into the tip.
- Dispensing is done by pressing the plunger again to first stop (normal dispensing) or second stop (complete emptying).
Some advanced micropipettes work on the positive displacement principle, using a piston inside the tip that directly contacts liquid (useful for viscous/volatile samples).
Types of Micropipettes
Micropipettes can be classified on several bases:
1. Based on Volume Capacity
- Fixed Volume Micropipette – Delivers only a specific, pre-set volume (e.g., 100 µL). Best for repetitive tasks.
- Variable Volume Micropipette – Adjustable within a specific range (e.g., 10–100 µL). Widely used in research labs.
2. Based on Operating Principle
- Air Displacement Micropipette – Most common type; works by piston creating air pressure.
- Positive Displacement Micropipette – Piston comes into direct contact with liquid; ideal for viscous or volatile samples (e.g., glycerol, solvents).
3. Based on Mechanism
- Mechanical Micropipette – Manually operated with hand pressure.
- Electronic Micropipette – Battery-operated; more accurate, reduces hand fatigue, allows multiple functions (mixing, dispensing, multi-dispensing).
4. Based on Number of Channels
- Single-Channel Micropipette – One channel; suitable for simple experiments.
- Multi-Channel Micropipette – 8, 12, or 16 channels; used in ELISA, PCR, microplates to speed up repetitive pipetting.
Working Mechanism of Micropipette
- Attach a sterile micropipette tip.
- Set desired volume on display window.
- Press plunger to first stop and insert tip into liquid.
- Slowly release plunger → liquid is aspirated.
- Transfer tip to target container.
- Press plunger to first stop to dispense, and second stop to expel remaining liquid.
- Eject tip using ejector button.
Correct handling ensures accuracy and reproducibility.
Applications of Micropipettes
- Molecular Biology: PCR, DNA/RNA extraction, electrophoresis loading.
- Biochemistry: Protein assays, enzyme reactions.
- Microbiology: Culture preparation, inoculations.
- Pharmaceuticals: Quality control (QC), drug testing.
- Chemical Labs: Handling volatile and viscous liquids.
- Clinical Diagnostics: ELISA tests, blood sample processing.
- Education & Research: Routine lab experiments and training.
Uses of Micropipettes
- Preparing reagents and dilutions.
- Transferring small liquid volumes.
- Mixing solutions by repeated pipetting.
- Loading gels in electrophoresis.
- Adding solvents precisely in reactions.
Common Sources of Errors in Micropipetting
- Handling Errors – Uneven plunger pressure, improper tip attachment, or incorrect angle while pipetting.
- Tip Quality Issues – Poorly fitting tips cause leaks and inaccuracies.
- Liquid Properties – Highly viscous or volatile liquids (e.g., glycerol, ethanol) may stick to walls or evaporate.
- Calibration Errors – Inaccurate results if micropipette is not calibrated regularly.
- Environmental Conditions – Temperature and air pressure changes affect volume accuracy.
Calibration of Micropipettes
Calibration ensures accuracy and precision.
Steps to Calibrate:
- Use distilled water at room temperature.
- Set desired volume on micropipette.
- Aspirate and dispense into a pre-weighed container.
- Measure weight of dispensed water (1 g = 1 mL at 25°C).
- Repeat 5–10 times for accuracy.
- Calculate dispensed volume using:
- V = Z × W (V = volume, W = water weight, Z = density factor).
- Determine accuracy using:
- A = 100 × Vavg / V0.
Regular calibration avoids errors in experiments.
Limitations of Micropipettes
- Manual operation prone to errors.
- May cause cross-contamination if tips touch surfaces.
- Not accurate with viscous/volatile samples unless using positive displacement pipettes.
- Can damage fragile cells during pipetting.
- Requires regular calibration and careful handling.
Examples of Micropipettes
- Manual Micropipette (Eppendorf 003012 series): Color-coded, sterile, DNA/RNA-free.
- Mechanical Multi-Channel Micropipette (Eppendorf Move It®): Variable volume, autoclavable, durable.
- Piston-Type Micropipette (Bioevopeak PIPE-T): Single-channel, variable volume, online calibration.
- Electronic Micropipette (Eppendorf Xplorer® series): Battery-operated, fatigue-free, multiple functions.
- Electronic Pipette (Transferpette® BrandTech): Autoclavable, 0–5 mL, reverse pipetting and dispensing functions.
FAQs on Micropipettes
Q1. Why do micropipettes have two stops?
First stop for aspirating/dispensing set volume, second stop for clearing residual liquid.
Q2. Which micropipette is best for viscous liquids?
Positive displacement micropipettes.
Q3. How often should micropipettes be calibrated?
Ideally every 3–6 months depending on usage.
Q4. Why are micropipette tips disposable?
To prevent cross-contamination between samples.
Q5. Can micropipettes measure nanoliters?
Specialized nano-pipettes exist, but regular micropipettes are limited to microliters.
Conclusion
Micropipettes are among the most important tools in modern biology and chemistry labs. Their ability to handle tiny liquid volumes with accuracy makes them indispensable in research, diagnostics, and industry.
Different types (fixed, variable, single-channel, multi-channel, mechanical, electronic, air displacement, positive displacement) allow scientists to choose the right one for their needs.
In short: Without micropipettes, experiments like PCR, ELISA, DNA sequencing, and protein studies would not be possible.
References
- https://microbiologie-clinique.com/laboratory-micropipette.html
- https://www.sciencedirect.com/topics/engineering/micropipette
- https://www.microlit.us/micropipette-product-guide/
- https://www.depts.ttu.edu/meatscience/docs/Calibrating-a-Pipette-7-23-20.pdf