Re: Stability of Maxpar conjugated antibodies
The "no metal" baseline/threshold is something that, honestly, is still being worked out.
Most of the time, I use enough beads that I can see a tiny pellet in my well or tube, and therefore know that I *have* beads. And then assume that if I don't see signal, that the antibody didn't bind. I know from doing no-antibody control bead samples that the beads themselves don't have any signal in the Ln region.
Spherotech is developing some Eu-core beads. Since Eu is fluorescent, they can be used in flow and not photobleach. It's just a happenstance that it also makes them useful for CyTOF. I've gotten advanced samples of variable-Eu no-capture beads, and also constant-Eu variable-capture-density beads. Both sets are visible in the CyTOF. Unfortunately, I don't think they're in official release yet.
The main things you might want to play around with in these experiments is your Lower Convolution Threshold, and your Lower Event Length parameters. The default settings for both of those assume a decent amount of metal associated with your cell (usually driven by your Ir staining). Therefore, make sure you save your IMD file and try reprocessing it with different LCT and LEL values (usually much lower) to make sure you're actually "seeing" all your events.
The ideal bead for these experiments would be loaded with constant Cs133 (since I'm not using it for antibodies) to drive ion cloud size and signal intensities, and then have no-capture (baseline) through variable-capture beads in a ladder going up. But Fluidigm and Spherotech seem slow to capitalize on the idea.....
Mike