Bead Assay in Sepcon
I carried out the bead assay to monitor membrane integrity in Sepcon format. The sample (no RTP) was taken from #703 and put in DMEM(-FBS) @ RT with membrane side facing up. 15um polystyrene beads were allowed to settle on the membrane and images were taken. As can be seen, the membrane is still intact after 9 days w/o any discoloration!! Both the slits were intact till day 2, but one of the slits broke while I was trying to check for discoloration by taking out the Sepcon from the well. The stability is much higher as compared to what we have seen earlier (w/o Sepcon) where the membranes fail without lasting for a day.
PS: At the same time, I have come across discolored samples under same conditions and from the same wafer in 2-3 days. Hence, there is some sample to sample variability OR may be the layer of microbeads on the chip is preventing any chemical attack by the media (media is not changed over the period). But this is hard to infer as there are areas on the intact membrane which are not covered by the beads and hence are exposed to the media.
What are the beads suspended in initially? Does adding beads change the pH? Without the SepCon and without the beads, on what day would you expect discoloration?
You guys are really getting some strange results…9 days – WOW!
The beads are plain or carboxylated polystyrene suspended in water with 0.1-1.0% dyestuff (black, blue, red, yellow, fluorescent, etc.). I am not sure if the pH changes by adding these. I will make sure to check it next time. W/o Sepcon and w/o beads, @ RT in DMEM-FBS, we can expect complete discoloration in anywhere between 2-4 days.