Investigations in high-precision sorting.

We have investigated the accuracy with which droplets containing cells can be sorted individually onto known and thus relocatable positions. The presence and random arrival of cells and particles in the sorter jet disturbs the orderly production and deflection of droplets, causing a dispersion of sorted droplet trajectories. The magnitude of this dispersion is a function of the phase relationship between the arrival of a cell at the end of the jet and the droplet formation. Using a modified Becton Dickinson Fluorescence-Activated Cell Sorter, we selected for sorting only those droplets that formed with a cell near the center of the droplet. We used this technique to sort Lewis lung tumor cells. The dispersion of droplet positions was reduced from over 3% to about 1% of an average deflection of typically 15 mm for a nozzle with a 50-micron diameter orifice. Sorting onto a surface such as magnetic tape or a microscope slide introduces another uncertainty in position because the cell may be located anywhere within the wetted radius of the droplet on the slide. Sorting onto less-wettable surfaces reduces the wetted radius and thus the variation in cell position.