A Simple Cell Sorter Monitor
Francis L. Battye
The Walter & Eliza Hall Institute
In every laboratory employing "stream-in-air" cell sorting, a great proportion of the available sorting time is wasted by the ubiquitous problem of nozzle orifice obstruction. When sorting small minority populations, a nozzle obstruction causing mis-direction of the unsorted stream into a sample collection tube can undo in seconds a sort which may have taken several hours. A sample may also be insidiously contaminated if the event occurs and then corrects itself without the operator observing it. Such problems may also be more subtle, like, for example, a sudden or gradual change in droplet breakoff position which may be caused by pressure supply fluctuations, by obstruction of sheath supply filters in the course of hours of operation, or by exhaustion of the sheath supply. There is therefore a need for some mechanism to continuously monitor the sort and protect the collected sample from catastrophe.
A simple system has been devised which monitors the stream direction and the amplitude and phase of droplet formation. This device focuses infra-red light, of wavelength 940nm, from a light emitting diode onto the saline stream and detects the droplet-modulated reflection. The illumination wavelength is well above the emissions of fluorochromes currently used in flow cytometry. The surveillance system may also monitor other possible fault situations caused by running out of cell sample or by blockage of the sample inlet lines. In the event of any of these conditions, the device acts to cover the collection tubes, stop the input of cell sample and switch off the high voltage to the deflection plates. Thus, for a total component cost of the order of $200, experiments involving in their preparation, investment of many technician-hours and quantities of expensive consumables, may be protected from sudden, tragic abortion.
