PCR tubes come in several standard sizes:
– 0.2 ml tubes – Typically used for individual PCR reactions. Around 5-6 inches long with a conical bottom. Can hold 10-100 μl reaction volumes.
– 0.5 ml tubes – Larger capacity for master mix preparation. Around 6 inches long. Hold 50-250 μl volumes.
– 1.5 ml microcentrifuge tubes – Used for larger scale PCR preps or post-PCR steps. Standard 1.5 ml tube size. Hold 0.5-1.5 ml.
– 0.1 ml tube strips/plates – Low profile 0.1 ml tubes connected in 8- or 12-tube strips. Allow use in 96-well PCR machines.
– 0.2 ml tube strips/plates – Same concept as above but in 0.2 ml tube size.
The small conical shape of standard 0.2 ml PCR tubes allows efficient heat transfer during thermocycling. The tubes are designed to fit in most PCR machine heating blocks.
Larger tubes are used when reaction volumes exceed 20-200 μl, the typical capacity of 0.2 ml tubes. They provide extra headspace needed for mixing larger reactions.
The tube strips or plates integrate PCR tubes with 96-well microplate format. This allows for higher throughput PCR.
So in summary, 0.2 ml is the standard PCR tube size but other sizes accommodate different reaction and throughput needs.
