We have seen quite a bit of variation in our transfection efficiency based on the number of passages prior to transfection. Do you have advice on the best passage number?

Answer

We have seen this as well throughout our labs. Since we identified this issue, we have implemented a standard best practice of only utilizing cells for transfection between 5- 20 passages because at a low passage there is very low transfection efficiency and at a higher passage the optimal dose of transfection shifts. We have also implemented the standard use of a positive control within each transfection experiment to quantitatively determine and track efficiency from week-to-week.