Helios injector on CyTOF2
We recently did a little testing to see whether we could stick a Helios injector on our CyTOF2 to gain some of the advertised benefits of smaller ion cloud size, which should provide higher signal intensity and reduced doublet incidence.
I set our flow rate to 30uL/min and successfully optimized our makeup gas at this level to get a nice boost in signal intensity with tuning and with beads. The bead CV was also terrific. However, when running cell samples we strange saw a reduction in cell signal intensity for most markers, despite the fact that the bead signal intensity was higher. I've attached some example plots:
Does anyone have any thoughts as to what might be going on?
I suspect this relates to the minimum event length cutoff, which was set to 10. As expected, the Helios injector produced events with a much shorter event length, and it almost seems like they might be "clipped" off. This does raise an interesting question regarding what exactly the minimum event length threshold is doing. I was under the (perhaps erroneous) impression that the event length threshold should act like the signal threshold on a cytometer, where if an event signal doesn't exceed the threshold that event doesn't get detected. However, if an event does cross the minimum threshold then all the signal associated with that event is collected. This would mean that an over-agressive threshold would reduce the overall number of detected events, but should affect the event-associated signal intensity; however in this case it seems like there may in fact be an effect on signal intensity as well.
Icahn School of Medicine at Mount Sinai, NYC