This article appeared first in “Inside Cell Culture”, the monthly newsletter for cell culture professionals
Particles in the microinjection solution can quickly clog the fine opening (around 0.5 µm) of an injection capillary and prevents further microinjections with this capillary. Capillary exchange in general means slowing down of the injection experiment and increased time outside the incubator. However, the frequency of capillary exchange depends not only on the type and concentration of the microinjection sample, but also on the quality of the sample preparation.
For proper preparation of microinjections, all buffer solutions should be filtered through 0.2 µm pore size filters before adding the injection sample. And most importantly, the injection sample should be centrifuged for 15 - 20 min at 4 °C (approx. 16,000 x g) just before loading the supernatant into the microinjection capillary. This significantly reduces any precipitation in the sample and effectively prevents a clogged microcapillary.
Furthermore, your sample-loaded microcapillary should enter the medium of your injection dish with a continuous flow at low pressure generated by the microinjector (compensation pressure). This keeps the solution moving with the molecules, reducing the risk of clogging by debris from the medium surface. It also prevents the medium from entering the microcapillary by capillary forces, which would dilute the injection solution and impact your microinjection experiment.