When submitting cell pellets and PBMC, the minimum cell concentration we need is 5*10^6 cells/mL in order to yield enough DNA for library preparation. If your research facility doesn’t have a cell counter on hand or your concentration is a bit lower, consider sending a larger volume of sample and let The Sequencing Center know so we can adjust our protocols for maximum DNA extraction efficiency. This is an easy first step to start your project with minimal delays.
If you plan to submit extracted DNA, start by referring to our sample submission guidelines for required concentration values. During library preparation the DNA will go through enzymatic shearing and replication phases, so higher DNA concentrations ensures that your sample will maintain enough integrity. Samples on the threshold of the minimum concentration risk becoming too fragmented and may fail to pass quality control points later on in library prep. These late stage failures can delay a project and may require a complete re-submission of the sample.
Many labs use spectrophotometers for DNA concentration checks, but we recommend using a fluorometer whenever possible. Fluorometers specifically quantify only double stranded DNA, whereas spectrophotometers are known to also register RNA, proteins, and other contaminants that can skew the concentration value. Having an accurate concentration value increases the likelihood that your sample will pass all downstream quality control checks.