Flow cytometry is a laser-based technology which is becoming increasingly popular in plankton ecology as it enables automated counting of individual cells, which can be distinguished based on their specific scatter and fluorescence signatures. Flow cytometers consist of a fluidic system where the water sample containing the cells is jacketed by a fast moving fluid in such a way that the cells pass a laser one by one. Light scatter and fluorescence emitted by the cells is recorded in the detector unit and subsequently processed to characterize the cells.
The research unit Biological Oceanography operates an Accuri C6 (BD Biosciences), a Cytosense (Cytobuoy) and two BD FACSCalibur flow cytometer. Both are bench top machines, ideally suited for fieldwork. The Accuri C6 is used primarily to count smaller autotrophs, bacteria, and viruses since the machine has extremely sensitive detectors. The Cytosense is used for larger organisms as it can handle larger volumes. It also takes photographs of individual plankton organisms which greatly facilitates characterization of the counted cells.
Examples for detection signals from two analysed ciliates and diatom cells in a chain deriving from a seawater sample.