Tue Dec 01, 2015 4:26 pm by mleipold
Hi Kalle,
I'm not sure what you mean by "is it possible to measure in several "windows" at the same time? i.e measure 100-190da and at the same time 400-490da but give less spectras for each window?"
The CyTOF acquisition window as normally set up for a v2 or a Helios runs from about masses 80Da to 209Da (so, slightly below Y up through and including Bi), so a width of about 140 Da. I think there's some confusion about terminology here: by the use of "mass" or "Da", we are talking about the mass of an *individual* metal ion (protons+neutrons), not the molecular weight of an organic molecule or the weight of a nondissociated nanoparticle/metal cluster. As such, there's no measuring up to 400-490Da, as there's no isotope of any element that has a mass of 400 Da.
As I understand it, if a given cluster isn't completely ionized, it just won't be measured quantitatively. By that, I mean whatever *does* get burned off the outside of the particle and is therefore dissociated into single metal atoms and ionized, *would* get measured. But the remnants of the undissociated core wouldn't enter the machine properly: I'm not sure it would even make it past the cones, and would certainly be the wrong mass to make it through the quadrupole mass filter upstream of the TOF chamber. (Fluidigm or another mass spec guru, please correct me if I'm wrong).
Regarding the Qdots: commercially-available Qdots made for fluorescent flow cytometry are currently made from natural abundance Cadmium (in the form of CdS, CdSe, and/or CdTe). Therefore, they are a mixture of several different isotopes of Cd.
While the exact ratio depends slightly on the exact source (mine) for the Cd, typical natural abundance from sheets listed in the Resources section here on Cytoforum would be:
106Cd= 1.25%
108Cd= 0.89%
110Cd=12.49%
111Cd=12.80%
112Cd=24.13%
113Cd=12.22%
114Cd=28.73%
116Cd= 7.49%
As you can see, several of these Cd isotopes are the same mass as the isotopes of some other useful metals (106-110Pd, 113In, etc). This impacts your panel design options. This also means that it is common to monitor only one channel for a Qdot probe: 114 or 112 are good choices, as they don't share masses with any other reagents that we currently use, and are a high percentage of the total Cd mass. Yes, technically, by monitoring only the 114 channel you are throwing away ~70% of your signal, but since each Qdot is a nanoparticle made of hundreds of metal ions, you can "afford" the loss.
Mike