Examples of common applications and their requirements*:
Incubation at high temperatures
In general, the higher the temperature to which the plate is subjected, the tighter the PCR plate seal must be in order to prevent evaporation of the samples. A technique which was commonly carried out in the past – and nowadays only in specific cases – employed a “liquid lid”, i.e., an overlay using mineral oil. With the closure options available today, the best protection is achieved through heat sealing using film or foil. The following specific examples illustrate additional sealing options, and their limitations, respectively:
- Incubation in the heating block/water bath: Sealing mats can be used if their nubs seal the plate wells tightly. Adhesive closures are also suitable if their adhesive does not have to be activated by pressure or heat (cycler lid).
- PCR: The contact pressure (and heat, if applicable) of the cycler lid improves the seal of the wells, allowing the use of adhesive films and foils that are thus activated, as well as cap strips.
- Real-time PCR / qPCR: The course of the reaction of a real-time PCR / qPCR is monitored optically. Since most systems detect from above, transparent closures with high light transmission are (almost) exclusively suited to this application. Accordingly, heat sealing films, and adhesive films (with an adhesive which will not impede light transmission) may be used, as well as flat or inverted cap strips.
Samples are stored at different temperatures, for different periods of time. For short-term storage at ambient or refrigerated temperatures (approx. 4 °C), or at freezer temperatures (approx. -20 °C), practically all closure types are appropriate. But how about long-term storage, ultra-low temperatures (-80 °C) or storage of special samples?
- Storage at -80 °C: With the exception of the adhesive films and foils, all other sealing options may be used at these temperatures.
- Long-term storage: Heat-sealing film is the best option for long-term storage; in addition to providing the tightest seal, it also protects from accidental perforation. Heat sealing foil and cap strips (for PCR plates) are good alternatives.
- Storage of light-sensitive samples: All foil-based closures provide good protection from light (heat seal and adhesive).
* The properties of the respective products, and the recommendations within this paper, are based on sealing options by Eppendorf. Similar products offered by other manufacturers may feature properties which differ from those described herein.