PCR Plates: How To Seal A PCR Plate?

Why Is PCR Plate Sealing Essential?

During PCR thermal cycling (often above 95°C), improper sealing can lead to several critical issues:

1. Sample evaporation
   Loss of reaction volume alters reagent concentrations and affects amplification efficiency and Ct values.

2. Cross-contamination
   Aerosols or splashing can introduce foreign DNA, resulting in false positives.

3. Well-to-well variability
   Uneven sealing leads to inconsistent reaction conditions across wells.

4. Instrument contamination
   Poorly sealed plates may contaminate thermal cycler blocks and increase maintenance costs.

What Are the Common Methods for Sealing PCR Plates?

In PCR (Polymerase Chain Reaction) workflows, the method used to seal PCR plates plays a critical role in maintaining reaction stability, preventing evaporation, and ensuring data accuracy and reproducibility. Common PCR plate sealing methods include the following:

1. Adhesive PCR Plate Seals

Optical adhesive film for PCR is the most widely used method for sealing PCR plates. These films use pressure-sensitive adhesive and can be applied at room temperature without special equipment.

• Key features: Easy and fast application; Reliable sealing to reduce evaporation; Optical-grade films available for qPCR fluorescence detection.
• Typical applications: Conventional PCR; Real-time PCR (qPCR); Routine laboratory workflows.
• Advantages: Easy and fast to apply without special equipment; Cost-effective and widely available; Optical-grade films suitable for qPCR; Ideal for high-throughput workflows.
• Limitations: Sensitive to application technique; air bubbles may occur; Less effective than heat sealing under prolonged high temperatures; Resealing reduces sealing performance.

2. Heat Sealing Films

Heat sealing films require a dedicated plate sealer, which uses heat and pressure to permanently bond the film to the PCR plate.

• Key features: Superior sealing integrity; Excellent resistance to evaporation; Suitable for high-temperature cycling and long-term storage.
• Typical applications: High-sensitivity PCR and qPCR; Sample storage and transportation; Experiments requiring maximum sealing reliability.
• Advantages: Easy and fast to apply without special equipment; Cost-effective and widely available; Optical-grade films suitable for qPCR; Ideal for high-throughput workflows.
• Limitations: Sensitive to application technique; air bubbles may occur; Less effective than heat sealing under prolonged high temperatures; Resealing reduces sealing performance.

3. Pressure-Sensitive PCR Plate Sealing Film

• Key Features: No heat sealer required, adheres at room temperature; Suitable for qPCR and fluorescence detection; Ensures reliable sealing for each experiment; Most films tolerate PCR cycling temperatures above 95°C; Suitable for standard 96-well or 384-well PCR plates.
• Typical Applications: qPCR experiments; Conventional PCR assays; High-throughput laboratory workflows; Fluorescence-based real-time detection.
• Advantages: Easy and convenient to use, no equipment needed; Cost-effective and economical; Compatible with optical detection, ensuring reliable data.
• Limitations: Sensitive to application technique; bubbles or uneven adhesion may occur; Slightly less effective for long-term high- or low-temperature storage compared to heat sealing; Not suitable for repeated opening or reuse.

4. Silicone Sealing Mat

Cap mats are single-piece covers designed to seal all wells of a PCR plate simultaneously, often made of silicone or other elastic materials.

• Key features: Covers the entire plate at once; Pierceable for automated pipetting; Suitable for high-throughput and automated systems.
• Typical applications: Automated liquid handling systems; High-throughput PCR workflows.
• Advantages: Covers the entire plate at once, improving efficiency; Pierceable options suitable for automation; Reusable depending on material.
• Limitations: Higher cost compared to disposable films; Requires cleaning and maintenance; Sealing uniformity depends on proper placement.

5. Aluminum PCR Plate Seal

Aluminum foil PCR films are usually applied by heat sealing and provide excellent barrier properties.

• Key features: Outstanding protection against evaporation and contamination; Excellent moisture and gas barrier performance; Ideal for long-term storage.
• Typical applications: PCR product storage; Sample transport; Non-optical PCR applications.
• Advantages: Superior protection against evaporation and contamination; Excellent moisture and gas barrier properties; Ideal for long-term storage and transport.
• Limitations: Not compatible with optical detection methods; Usually requires heat sealing equipment; Cannot be resealed once opened.

How To Use A Plate Sealing Film？

1. Preparation

• Select the appropriate sealing film according to your application

  • PCR / qPCR: Optical or pressure-sensitive sealing film

  • Long-term storage or solvents: Aluminum heat sealing film

  • Cell culture: Gas-permeable or semi-permeable sealing film

• Ensure the plate rim is clean and dry

• Wear gloves to avoid contamination or fingerprints

2. Sealing Procedure (Pressure-Sensitive PCR Sealing Film)

In order to seal the PCR plates better, to apply downward pressure with a certain force with the scraper.

• Align the sealing film with the PCR plates to ensure the film covers all the holes, and use the flat edge of the sealing scraper to move back and forth along the long and short edges of the plate respectively and apply certain pressure.
• Stand up the sealing scraper, move and press it crosswise horizontally and vertically between all the wells of the plate. Then gently move it back and forth along the edges of the PCR plates all around and press it at each corner, be sure that the film securely seals all the edges of the reaction plate to make sure that the outer wells are properly sealed and the sealing is completed.

3. Heat Sealing Film Tips (Aluminum Foil)

• Set proper heat sealing parameters (typically 160–170°C for 3–5 seconds)

• Allow the plate to cool naturally before handling

• Avoid reheating the same plate multiple times

4. Precautions

• Avoid repeated peeling and resealing

• Ensure full adhesion before centrifugation

• Use optical-grade films for fluorescence detection

• For long-term storage, aluminum heat sealing films are recommended

5. Troubleshooting

• Air bubbles present: Reapply the film, pressing from center outward

• Evaporation or leakage: Switch to higher-adhesion or heat-sealed films

• Weak fluorescence signal: Confirm the film is optically clear

Selection of Sealing Film 

PCR and DNA sequencing library preparation experiments

Most of microplates for PCR are made of polypropylene, which is easy to seal, not easy to curl, and resistant to suitable temperature. The purpose of sample sealing is mainly to prevent the evaporation of samples and reagents in PCR thermal cycling, so as to avoid affecting the experiments results.

For this kind of experiment, it is recommended to use sealing film that is easy to puncture . Because this kind of experiment needs to be followed by the collection of experimental products, it is particularly important to absorb the liquid with a single-well or multi-well pipetting device as required.

Plastic films are less penetrable and are not suitable for this kind of experiment. It should be noted that due to the thermal expansion and contraction of the microplate brought about by PCR thermal cycling and the volatilization of organic reagents such as DMSO, poor quality aluminum films may burst and liquid will leak during the experiment.

Fluorescence quantitative PCR experiment

The sealing film for fluorescence quantitative PCR experiments should have good light transmission for the accurate detection of fluorescence signals while ensuring the short-term sealing of the experiments. Our common solutions are translucent self-adhesive film and  pressure-sensitive film.

The choice of these films is generally based on personal habits of use.

Summary

Although PCR plate film may seem like a routine step, it plays a critical role in ensuring data accuracy and reproducibility. As PCR technologies continue to expand into clinical diagnostics, food safety, and environmental testing, the importance of reliable sealing solutions becomes increasingly evident. By selecting appropriate sealing methods and following standardized best practices, laboratories can minimize evaporation, contamination, and variability, ultimately improving experimental outcomes. Proper PCR plate sealing is not just a technical detail—it is a foundation for trustworthy results.