Why are filter tips mandatory for PCR work?

During pipetting, aerosols are generated — fine droplets that can travel upward through the tip and into the pipette barrel. In PCR, even nanogram quantities of contaminating DNA or PCR product entering the barrel are enough to cause false-positive results in subsequent runs. Filter tips contain a hydrophobic polyethylene filter inside the tip shaft that physically blocks aerosols and liquid from travelling beyond the tip. Filter tips are mandatory for all PCR setup, RT-PCR, sequencing, and RNA handling. Standard non-sterile tips are not acceptable substitutes for this work.

What is the difference between low-retention tips and standard tips?

Standard polypropylene tips allow a thin film of liquid to adhere to the inner tip surface, which is not significant for most aqueous samples. Low-retention tips have a modified hydrophobic inner surface that minimises this adhesion, resulting in more complete liquid delivery and better volume accuracy. They are used for viscous samples, concentrated protein solutions, expensive or scarce reagents, and any situation where even a small residual volume left in the tip represents a meaningful loss or accuracy problem.

When should wide-bore pipette tips be used?

Wide-bore tips have an enlarged orifice compared to standard tips. They are used when the sample contains intact cells, blood, dense cell suspensions, or any particulate material that would be sheared or clogged by the narrow opening of a standard tip. Shearing cells through a narrow tip orifice damages cell membranes, affects cell viability, and produces inaccurate counts in haemocytometer or flow cytometry applications. Wide-bore tips allow these samples to pass through without mechanical damage.

Can non-sterile autoclavable tips be used for RNA work?

No. Autoclaving kills microorganisms but does not reliably eliminate RNase activity. RNases are extremely heat-stable enzymes that can survive autoclaving and degrade RNA samples on contact. For RNA extraction, RT-PCR, and any procedure involving RNA, only certified RNase-free pre-sterile tips should be used — these are manufactured and packaged under conditions that confirm absence of RNase, DNase, ATP, and endotoxins, and come with a sterilization certificate.

What does tip colour indicate?

Tip colour is a size indicator, not a sterility indicator. Yellow tips typically correspond to the 200 µL volume range; blue tips to the 1000 µL range; white or clear tips to the 10 µL range. Colour coding is largely standardised across major manufacturers but can vary — always confirm the volume range on the packaging label. Sterility status is stated on the packaging, not indicated by colour.

Why should tips never be touched by hand before use?

Human skin carries RNases, DNases, and microorganisms that transfer to the tip on contact. For molecular work, skin RNases degrade RNA samples; for microbiology culture work, skin commensals introduced on a tip can appear as contaminants in culture results. Tips should always be attached using the pipette's tip ejector mechanism pressing into the tip rack, and removed using the tip ejector button — hands should never contact the tip body or orifice.

Pipette Tips: Types, Uses, and Criteria to Choose It

In a molecular diagnostics laboratory, a technician is setting up a batch of 24 hepatitis C virus RNA PCR tests. She uses standard non-sterile tips — the same tips used for routine serological work — because the filter tips box is empty and she does not want to delay the run. The PCR runs overnight. The next morning, two negative control wells show amplification. The entire batch is invalid.

What happened: standard tips allow aerosols generated during pipetting to travel up into the pipette barrel. PCR product from a previous run — invisible, present in nanogram quantities — had contaminated the barrel. When the next run was set up, that contamination transferred into the negative control wells through aerosol carry-over. Filter tips, with their hydrophobic barrier inside the tip shaft, would have blocked the aerosol completely.

The pipette tip is not a passive plastic attachment. It is the aseptic barrier between the specimen and the pipette. Choosing the wrong tip type does not just affect accuracy — it can invalidate an entire diagnostic run.

Pipettes are the laboratory equipment used for handling liquid samples. Almost all the pipettes require pipette tips for performing their intended work.

Pipette tips are the attachable part of pipettes that aid in aspirating and dispensing liquids. Most commonly used tips are disposable or autoclavable. These are also available in various types like non-sterile or one-time use (used for general laboratory procedure), pre-sterile (used for cell cultures), and filtered tips (used for handling RNA and DNA) .

Pipette tip made up of virgin polypropylene is the most common and environmental friendly one. Sometimes the tips also contain plastics or metal additives (yellow and blue colored tip).

Pipette tips - Different types of pipette tips Figure: Different types of pipette tips

Why the Pipette Tip Is the Critical Component

The design of a micropipette is built around one principle: the liquid must never contact the pipette barrel. The barrel contains the piston, the spring mechanism, and the air column that drives aspiration and dispensation. If liquid or aerosol enters the barrel, the pipette becomes a contamination source — transferring material from one sample to the next through every subsequent pipetting step until the barrel is decontaminated.

The pipette tip makes this separation possible. Liquid enters the tip only. The air cushion between the liquid and the piston ensures the liquid goes no further. The tip is discarded after each use, taking any biological material with it.

This design works — unless the aerosol generated during rapid aspiration or dispensation travels upward past the air cushion and reaches the barrel. This is what filter tips prevent. The hydrophobic polyethylene filter inside the tip shaft physically blocks aerosols and liquid from travelling upward, regardless of pipetting speed or technique.

Understanding this mechanism is what makes tip selection a clinical decision, not just a procedural one.

Types of Pipette Tips

The pipette tips are divided into several types based on their functions and properties. One basis for differentiating the types of pipettes is sterility. Some tips might be sterile and RNase-free (filter tip). In contrast, non-sterile tips are generally autoclavable and useful in simple laboratory experiments like serological tests.

Another basis is their purpose; some require a more extended head to prevent contamination (long tip) or may require precise measurement (low retention tips). Finally, the last basis for differentiation is size; 0.1 to 1000 µl is available in universal (non-sterile) pipette tips.

The types of tips and their functions are as follows:

Based on sterility

Sterile or Pre-sterile Tips

These are one-time use tips that come in the pre-sterilized form. These tips are free of DNA, RNase, ATP, and pyrogens and suitable for experiments that require sterile conditions like cell cultures, PCR, etc. These are also helpful while handling volatile liquids and specimens that require testing in a contamination-free environment.

Non-sterile Tips

These are the most commonly used tips, and also known as universal or general purpose pipette tips. These tips are not sterile because they are not certified as free of RNase, DNA, pyrogens, etc. These are applicable in simple laboratories for handling liquid specimens and reagents that are not volatile or do not have high contamination risk.

Based on purpose

Filter Tips

Pipetting creates aerosols that carry the risk of cross-contamination. The filter tips are fitted with a filter to avoid the formation of aerosols. This type of pipette has been helpful in PCR (polymerase chain reaction), handling RNA/DNA, radio-labeled, infectious, and volatile samples.

Low-retention Tips

These tips withhold less liquid than generally used ones, which help preserve samples/reagents. These tips are good for viscous and highly concentrated samples. However, these pipette tips are very costly. These are ideal for electrophoresis , protein analysis, sequencing, or any tests that use viscous and concentrated liquids.

Long Tips

Sometimes the reagents or samples have a minimal volume and are at the bottom of the container. It means putting not only the pipette tip but also the shaft of the pipette inside the container. This increases the risk of contamination, so using a pipette tip that is longer than usual ones is the best substitute.

Short Tips

The extended tips become inconvenient when the samples are drawn or placed into small wells. So, using short tips with a multichannel pipette is the perfect fit. Likewise, pipetting with long tips can strain the hands and require wider bench space. So, switching to shorter tips in order to avoid these conditions is the best option.

Wide Bore Tips

Sometimes the samples that a laboratory handles can be fragile and deteriorate while transferring from a narrow area of the standard tips. So, using tips with a wide orifice is the best option for handling samples involving cells or that are very dense.

Based on size

The pipette tips based on the size range from 0.1 to 1000 µl for non-sterile/general purpose pipettes. 200 µl and 1000 µl tips are used in serological tests and school laboratory experiments. Whereas for filter tips, these range from 0.1 to 1250 µl. These are available in bulk or a box.

Which Tip Type for Which Procedure?

Procedure	Recommended tip	Reason
PCR setup (master mix + template)	Filter tip — mandatory	Aerosol carry-over from PCR products invalidates reactions; filter blocks barrel contamination
RNA extraction and handling	Filter tip — mandatory	RNases are ubiquitous; any barrel contamination introduces RNase degradation of sample
DNA sequencing setup	Filter tip — mandatory	Carry-over contamination produces mixed sequencing signals
ELISA (serum/plasma samples)	Standard sterile or non-sterile	No amplification step; low contamination risk; filter tips optional
Routine serological dilutions	Standard non-sterile	General purpose; no nucleic acid amplification involved
Cell culture work	Sterile (pre-sterile, pyrogen-free)	Cells are sensitive to endotoxins and microbial contamination
Viscous samples (glycerol, serum concentrates, protein solutions)	Low-retention	Reduces sample left in tip; improves volume accuracy and sample recovery
Blood, cell suspensions, viscous biological samples	Wide-bore	Prevents cell shearing or clogging through narrow standard tip orifice
Samples at bottom of narrow containers	Long tips	Prevents shaft contamination when tip must be inserted deeply
Multichannel pipette — plate transfers	Short tips	Shorter tips fit microtiter wells without hitting the plate bottom
Infectious specimens (BSL-2/BSL-3 work)	Filter tip	Protects pipette barrel and reduces aerosol exposure risk to operator
Radioactive or volatile samples	Filter tip	Prevents volatile or radioactive material from entering the barrel

Uses of Pipette Tips

The tips are integral to any pipetting device, from manual to automated. The pipette tip helps to increase pipetting speed and prevent contamination. So, these have utmost use in the laboratory handling liquid samples.

Criteria for Choosing the Right Pipette Tip

The main criteria for choosing the right pipette tip is the experiment you conduct in your laboratory. Sterile filter tips are a must if you are attempting molecular tests in the laboratory. Along with the experiment, there are many more criteria to consider before buying the tips. They are as follows:

Volumes of Liquid Handled

The volume of liquid samples or reagents varies widely in the laboratories. In the laboratory, it is best to have tips of various sizes and purposes.

Pipette Used

If you are handling multiple samples in a limited time, you might use a multichannel pipette. Still, general laboratories use micropipettes, so buying the tips suitable for both types in bulk is more economical.

Preferred Company

For sterile tips, confirm the manufacturer provides a sterilization certificate specifying that tips are certified free of DNA, RNase, ATP, and endotoxins.

Budget

Your budget is the second main criterion for choosing a suitable pipette for your laboratory. The filter tips are costly as compared to general-purpose tips. So, if the budget is tight and you are not willing to perform any molecular tests, then buying just general-purpose tips is the best choice.

Handling of Pipette Tips

Handling pipette tips is a crucial step in minimizing laboratory errors. Some points to consider while performing the laboratory work are as follows:

Maintain the right temperature during storage and while performing tests. Bring the tip and all the equipment to room temperature.
If you use general-purpose pipette tips, rinse it correctly with the sample/liquid you are aspirating to avoid delivering the incorrect volume of the liquid.
Do not use your hands while removing or placing the pipette tips in the pipette to avoid cross-contamination.
Pipetting technique should be standard. Press the plunger to the first stop and immerse it into the liquid to aspirate the sample. While dispensing, press the plunger up to the second stop (double press) to dispense all the liquid.
Immersing the pipette tip up to the correct depth is also important.
While aspirating the sample and pulling it out from the container, hold the pipette vertical.
Check the pipette tips before and after dispensing, to ensure the liquid is dispensed completely.
The force applied while pressing the plunger should be consistent.

Common Pipette Tip Errors and Their Consequences

Error	Consequence	Prevention
Using standard tips for PCR	Aerosol contamination of barrel; PCR product carry-over; false positives in negative controls	Use filter tips for all PCR work — non-negotiable
Reusing tips between samples	Cross-contamination; organisms or nucleic acids from one sample enter the next	One tip per sample; use tip ejector, never hands
Touching tip orifice with fingers	Skin microbiota introduced; RNases from skin degrade RNA samples	Always attach and remove tips using the ejector button and tip rack
Tip not fully seated on cone	Air leak; inconsistent aspiration volume; tip falls off during transfer	Press firmly until tip seats with a slight click; check all channels in multichannel use
Using wrong tip size for volume	Low-volume tips used for high-volume aspiration creates excessive suction; tip may crack or aspirate beyond capacity	Match tip size to pipette model and target volume
Storing tips without cover	Dust and environmental RNases settle into tips; molecular work contaminated	Keep tip boxes closed; use individually wrapped sterile tips for PCR and RNA work
Using autoclavable tips for RNA work	Autoclaving does not eliminate RNase activity unless DEPC-treated water is used	Use certified RNase-free pre-sterile tips for RNA handling

How to Remember

"The tip is the barrier — filter the barrier when the stakes are high." The tip separates the specimen from the pipette barrel. When the procedure involves nucleic acid amplification, infectious specimens, or RNA, that barrier must include a filter. For routine serological or culture work, a standard tip is sufficient. The question is always: what happens if barrel contamination occurs? If the answer is "invalid PCR run" or "patient misdiagnosis," use a filter tip.

Filter tip = anytime amplification is involved. PCR, RT-PCR, nested PCR, LAMP, sequencing — any procedure that amplifies nucleic acid is exquisitely sensitive to carry-over contamination. Filter tips are mandatory, not optional, for all of these.

Wide-bore for cells; low-retention for viscous. Wide-bore tips prevent shearing — cells, blood, and dense suspensions pass through without damage. Low-retention tips prevent sticking — viscous or concentrated samples cling less to the inner surface, improving volume accuracy and sample recovery. Two different problems; two different tip solutions.

Tip colour is size, not sterility. Yellow tips = typically 200 µL range. Blue tips = typically 1000 µL range. White/clear tips = typically 10 µL range. Colour coding varies slightly by manufacturer, but yellow and blue are the most standardised. Colour tells you volume range, not sterility status — check the packaging label for sterility information.

Key exam facts in one table

Topic	Key fact
Function of the tip	Aseptic barrier — liquid contacts only the tip, never the pipette barrel
Most common tip material	Virgin polypropylene — inert, low protein-binding, autoclavable
Filter tip — mechanism	Hydrophobic polyethylene filter inside tip shaft blocks aerosols and liquid from entering barrel
Filter tip — mandatory for	PCR, RT-PCR, RNA handling, DNA sequencing, infectious specimens, volatile/radioactive samples
Low-retention tips — used for	Viscous, concentrated, or expensive samples; reduces liquid adhesion to tip walls
Wide-bore tips — used for	Cells, blood, dense suspensions — prevents shearing through narrow orifice
Long tips — used for	Samples at the bottom of deep or narrow containers; prevents shaft contamination
Short tips — used for	Multichannel pipetting into microtiter plate wells
Sterile (pre-sterile) tips — certified free of	DNA, RNase, ATP, endotoxins, pyrogens
Non-sterile tips	General purpose; autoclavable; not certified RNase/DNA-free
Colour coding (general)	Yellow ≈ 200 µL; blue ≈ 1000 µL; white/clear ≈ 10 µL (varies by manufacturer)
Tip reuse	Never between samples — one tip per sample is non-negotiable
Autoclaving non-sterile tips for RNA work	Not sufficient — autoclaving does not eliminate RNase; use certified RNase-free tips

References

Clinical and Laboratory Standards Institute (CLSI). (2016). Clinical Microbiology Procedures Handbook (4th ed.). American Society of Microbiology. https://doi.org/10.1128/9781555818814
ISO 8655-1:2022. Piston-operated volumetric apparatus — Part 1: Terminology, general requirements and user recommendations. International Organization for Standardization.
Harkins, J. (2021). The different types of pipette tips and when to use them. INTEGRA Biosciences. https://www.integra-biosciences.com/global/en/blog/article/different-types-pipette-tips-and-when-use-them
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2018). Textbook of Diagnostic Microbiology (6th ed.). Elsevier.
Cheesbrough, M. (2006). District Laboratory Practice in Tropical Countries, Part 2 (2nd ed.). Cambridge University Press.