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Summary: NATURE BIOTECHNOLOGY VOL 17 NOVEMBER 1999 http://biotech.nature.com 1109
Conventional fluorescence-activated cell sorters (FACSs) are widely
used to study eukaryotic cell populations. Although they provide
impressively efficient sorting, they are costly ($250,000), mechanical-
ly complex, and require trained personnel for operation and mainte-
nance. Inexpensive devices that rapidly sort live cells, particles, and
even single molecules would greatly facilitate screening of combina-
torial chemistry libraries or cell populations during in vitro molecu-
lar evolution. Moreover, such devices would have wide applications
in clinical medicine and basic biological and materials research.
All modern conventional flow cell sorters are designed to have a flow
chamber with a nozzle and are based on the principle of hydrodynamic
focusing with the sheath flow15. In addition, most sorting instruments
combine the technology of ink-jet printing and electrostatic deflection
to achieve droplet generation and high sorting rates6,7. However, this
mechanism is delicate and many failures of the instrument can result
from problems in the flow chamber. For example, clogging of the orifice
and particle adsorption and contamination in the tubing can cause tur-
bulent flow in the jet stream, inducing variation in illumination and
detection. Sample carryover can occur during consecutive runs when
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