Patent ID: 8748183

Claim:
A method of continuously verifying proper sort calibration in a droplet sorting flow cytometer that selectively applies or does not apply one of a set of one or more electrical charges to a plurality of droplets as they form from a continuous fluid stream at a droplet break-off location and electrostatically sorts the droplets into two or more separate droplet streams, the selection of the electrical charge for each droplet being dependent on expected particles in the droplet based on a drop delay setting representing an estimate of the time elapsing between the moment a particle contained in the continuous fluid stream is detected at an interrogation location of the flow cytometer and the arrival of that particle at the droplet break-off location, the method comprising: selecting a fraction of droplets in one of said separate droplet streams estimated to have substantially zero probability of containing a particle; applying one charge of said set of charges to the fraction of selected droplets in order to form a calibration test stream out of the selected droplets; illuminating the droplets in the calibration test stream; and detecting any light emitted or scattered by any particles in the selected droplets.