PCR Plate Sealing Films vs. Caps: How to Prevent Evaporation and Choose the Right Seal
Have you ever experienced reaction volume loss or inconsistent results between wells during PCR or real-time PCR (qPCR)?
PCR involves repeated heating and cooling cycles to amplify DNA. If reaction tubes or plates are not properly sealed, evaporation may occur and affect experimental results.
This is particularly important in qPCR applications using small reaction volumes, where even a small amount of evaporation can change reagent concentrations and potentially influence measurement consistency.
Several sealing methods are available for PCR plates, including adhesive sealing films, cap strips, and heat-sealing films.
In this article, we explain the differences between PCR plate sealing methods, how to minimize evaporation, and what to consider when choosing sealing materials for PCR and qPCR.
1. What Happens When PCR Reaction Mixtures Evaporate?
PCR involves repeated temperature changes during denaturation, annealing, and extension.
The denaturation step typically requires high temperatures, making proper sealing of the reaction vessel especially important.
If a cap or sealing film is not securely attached, water may escape during thermal cycling, reducing the reaction volume.
As the reaction mixture evaporates, the concentrations of DNA, primers, enzymes, salts, and other reaction components may change.
These changes can affect amplification efficiency and reproducibility.
When using a 96-well PCR plate, evaporation may not occur uniformly across all wells.
For example, wells located near the edges of a plate may experience different conditions from those in the center, depending on the instrument's temperature distribution, sealing quality, and other experimental factors.
However, differences between wells cannot always be attributed to sealing problems alone. Reaction conditions, thermal cycler performance, and sample preparation can also influence results.
Maintaining reaction volume and ensuring proper sealing across all wells are important steps toward consistent PCR performance.
2. What Is the Difference Between PCR Plate Sealing Films and Caps?
Two common methods for sealing PCR plates are sealing films and cap strips.
PCR plate sealing films cover multiple wells by adhering to the upper surface of the plate.
For experiments involving a large number of reactions, such as a full 96-well PCR plate, sealing films can make it possible to seal the entire plate without attaching individual caps to each well.
Cap strips, on the other hand, typically consist of connected caps that fit into individual wells.
They can be convenient when using only certain rows or groups of wells, or when working with PCR vessels specifically designed for compatible cap strips.
Sealing films are also available with different attachment mechanisms.
Some use pressure-sensitive adhesives that bond to the plate when pressure is applied, while others require specialized heat-sealing equipment.
Each sealing method has different handling requirements and equipment considerations.
It would be incorrect to assume that sealing films always provide better sealing performance than caps, or that caps are necessarily more prone to evaporation.
Sealing performance depends on the materials, product design, compatibility with the PCR plate, and correct application.
3. Should You Use Transparent Sealing Films for qPCR?
Real-time PCR, commonly known as qPCR, measures fluorescence signals during DNA amplification.
Therefore, sealing materials used for qPCR must not only help prevent evaporation but also be compatible with the instrument's optical detection system.
For instruments that detect fluorescence through the top of the reaction vessel, the optical properties of the cap or sealing film can affect measurement suitability.
Optical sealing films are designed for applications where light transmission through the seal is important.
However, a transparent film is not automatically suitable for every qPCR instrument.
Factors such as film material, thickness, autofluorescence, and instrument detection methods should all be considered.
WATSON BIO LAB offers Titer Stick HC Film (547-KTS-HC), a pressure-sensitive plate sealing film designed for applications including real-time PCR.
The film uses a pressure-sensitive adhesive whose bonding strength increases as pressure is applied during sealing.
Proper application helps the film adhere securely to the plate surface and reduces the risk of peeling.
Its high transparency allows fluorescence measurements to be performed without removing the seal, making it a useful option for compatible qPCR applications.
Explore the product: Titer Stick HC Film – 547-KTS-HC
Note: This product is available by pre-order and is arranged from Japan. Please refer to the product page for shipping options and lead times.
Before use, confirm compatibility with the PCR plate material, plate geometry, and optical detection requirements of the instrument.
4. How Can You Properly Seal a PCR Plate to Minimize Evaporation?
The performance of a PCR sealing film depends not only on its design but also on how it is applied.
For example, if reaction liquid remains around the edges of the wells, or if dust and other contaminants are present on the plate surface, the film may not adhere evenly.
It is therefore important to check that the plate's upper surface is clean and suitable for sealing before applying the film.
For pressure-sensitive sealing films, sufficient pressure must be applied according to the manufacturer's instructions.
If insufficient pressure is applied, the film may not adhere securely, potentially leading to partial peeling or evaporation during thermal cycling.
At the same time, excessive pressure should be avoided if it could deform the plate or interfere with proper sealing.
Using the recommended sealing tools and procedures helps achieve more consistent results.
Another factor worth considering is the rim design around each PCR plate well.
The rim forms part of the contact surface between the plate and its sealing material, making it an important structural feature.
For example, WATSON BIO LAB's 0.1 mL 96-Well Non-Skirted PCR Plate (137-674C) features a carefully designed rim around each well.
This structure is intended to support secure sealing with compatible caps or sealing films.
Explore the product: 0.1 mL 96-Well Non-Skirted PCR Plate – 137-674C
However, the rim design alone does not guarantee compatibility with every sealing film.
Researchers should verify the specifications of both the PCR plate and the selected sealing material.
5. How Should You Choose a Sealing Method for PCR and qPCR?
The most appropriate sealing method depends on the experiment, reaction vessel, and equipment being used.
For conventional endpoint PCR, the main priorities include minimizing evaporation and leakage during thermal cycling and ensuring compatibility with the instrument's heated lid.
Depending on the equipment and consumables, cap strips or PCR-compatible sealing films may both be suitable options.
For qPCR, sealing performance remains important, but optical compatibility introduces additional requirements.
In particular, instruments that detect fluorescence through the top of the reaction vessel may require compatible optical sealing films or optically suitable caps.
The number of wells used can also influence the choice.
For example, when processing a full 96-well plate, sealing film may allow all wells to be sealed in a single operation.
On the other hand, when using only eight or sixteen wells, cap strips may be more convenient for certain workflows.
Cost is another factor to consider.
The overall cost of sealing films and cap strips can vary depending on the number of wells used, product pricing, additional accessories, and handling time.
Ultimately, researchers should evaluate sealing performance, optical compatibility, workflow efficiency, and cost together when selecting a PCR plate sealing method.
Conclusion: Choose PCR Sealing Methods Based on Evaporation Control and Measurement Requirements
PCR plates can be sealed using different methods, including sealing films and cap strips.
Both are intended to help minimize evaporation and leakage, but their suitability depends on product design, application procedures, and compatibility with laboratory equipment.
For qPCR, optical compatibility is an additional consideration because sealing materials may affect fluorescence detection.
Proper application is also essential for achieving effective sealing, particularly when using pressure-sensitive adhesive films.
WATSON BIO LAB offers PCR plates and sealing materials designed to support various laboratory workflows, including applications involving optical measurements.
When reviewing your PCR consumables, consider not only the reaction vessel itself but also the sealing method used to maintain appropriate reaction conditions.