From “How are Photomultiplier Tubes Used in Flow Cytometry?”(2020):

  • Flow cytometers use photodetectors to convert the light of excited fluorophores into photocurrent, which can be digitized.
  • Photomultiplier tubes are one of the most common types of photodetectors used in flow cytometry and are often preferred over other common photodetectors due to their increased sensitivity.
  • Photomultiplier tubes use cathodes and anodes set in a cold vacuum tube to generate photocurrent from the light generated by the flow cytometry.
  • The photon, generated by the excitation of the fluorophore in the sample, collides with a photocathode when entering the photomultiplier tube. This results in the creation, also known as photoemission, of electrons.
  • The electrons generated by the photocathode move between the dynodes that are placed cascading down the photomultiplier tube. The movement between the dynodes, which are also called electrodes, results in the generation of secondary electrons. This, in turn, leads to the signal being amplified.

From “Photomultiplier tubes do what other photon counters can’t (2020)”:

  • Photomultiplier tubes (PMTs) are one of the first devices developed that can detect single photons (Geiger counters can also count individual photons, but only of the gamma-radiation variety).
  • Since the advent of the PMT, many other photon-counting techniques have been invented, including avalanche photodiodes (APDs), single-photon avalanche diode (SPAD) arrays, superconducting nanowire single-photon detectors (SNSPDs), silicon photomultipliers (SiPMs), and microchannel plates (MCPs)—which are actually a compact form of PMT with many parallel channels.
  • So why is the original, discrete type of PMT still being used? The answer is that it has a combination of qualities that is preferable for numerous applications.

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