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Increasing the sensitivity of a FACScan flow cytometer to study oceanic picoplankton
Author(s) -
Dusenberry Jeflrey A.,
Frankel Sheila L.
Publication year - 1994
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1994.39.1.0206
Subject(s) - photomultiplier , sensitivity (control systems) , picoplankton , optics , fluorescence , environmental science , remote sensing , materials science , physics , detector , geology , biology , ecology , phytoplankton , electronic engineering , nutrient , engineering
Existing limitations on the sensitivity of commercially available flow cytometers do not permit the detection of extremely dim picoplankton cells, particularly Prochlorococcus marinus in near‐surface oligotrophic ocean waters. This problem was overcome by making some simple modifications to a FACScan (Becton Dickinson) flow cytometer to increase its sensitivity by about fivefold. The fluorescence and side scatter sensitivity was increased by replacing the existing focusing lens and beam‐steering mirror with a 3× expansion telescope and a slightly shorter focusing lens, resulting in a smaller laser spot size at the interrogation point. Forward scatter sensitivity was increased by replacing the existing photodiode with a photomultiplier tube, which has a background noise level about an order of magnitude lower. The fluorescence sensitivity of the modified instrument, measured with a quantitative fluorescence microbead standards kit, is 74 molecules of equivalent soluble fluorochrome for fluorescein. The instrument can now detect extremely dim P. marinus from open‐ocean surface waters.