Mass cytometry (CyTOF)
What is mass cytometry?
Put simply, mass cytometry replaces the fluorescent reporters used in fluorescence flow cytometry, with metal isotopes, which are detected using cytometry by time-of-flight mass spectrometry (CyTOF). This has expanded the number of parameters that can be detected simultaneously on single cells to approximately 40 (with >100 theoretically achievable), due to the absence of signal overlap between metal isotopes. This allows an investigator to measure an enormous number of extracellular and intracellular targets simultaneously.
How it works
The 'mass cytometry' methodology relies on the distinct atomic masses of individual metal isotypes, which are conjugated to antibodies specific for surface or intracellular antigens on single cells. Labelled cells are introduced into the machine by generating a liquid aerosol through a nebulizer, which passes sample through an argon-fuelled inductively-coupled plasma (ICP) torch, burning at approximately 7500 K. The ensuing ion cloud is then drawn into a vacuum, where ions of less than atomic mass 80 are removed from the samples, before the samples enter the time-of-flight chamber. This form of mass spectrometry ensures that metal ions with different atomic masses will arrive at the detector at different times, separated by the flight time required to pass through the chamber. Ions with larger atomic mass take longer to arrive than those of lower atomic mass. The resulting data is high-dimensional single-cell data, consisting of clean and distinct metal abundance peaks that correlate with cellular antigen expression.
For more information on mass cytometry at the Ramaciotti Facility for Human Systems Biology (RFHSB), and the Sydney Cytometry facility, see this ASI newsletter.