Method and apparatus for sorting particles

1. A droplet interference system for sorting cells according to chromosomal DNA characteristics, comprising:

a flow cytometry apparatus for delivering a fluid stream containing the cells to a first location;

an optics system operable to direct a laser beam from a laser to the first location so that the cells pass through the laser beam resulting in emissions of electromagnetic radiation from the cells, wherein the optics system is operable to collect the emissions of electromagnetic radiation produced by cells at the first location; and wherein the optics system further comprises a photodetector to detect and convert at least some of the emissions into electrical signals indicative of the chromosomal DNA characteristics;

a processor in communication with the photodetector to classify the cells according to the chromosomal DNA characteristics and to produce sort decisions to sort selected stream segments according to the classification of the cells contained in the stream segments; and

a droplet generating system in communication with the processor producing a droplet interference stream, wherein the droplet generating system is operable to divert a droplet from the droplet interference stream which hits the fluid stream at a second location downstream of the first location, thereby separating the selected stream segments and the cells contained therein from the fluid stream.

2. The system as claimed in claim 1 , wherein the photodetector is located on a beam axis of the laser to the rear of a focusing lens.

3. The system as claimed in claim 1 , wherein the cells are sperm cells and the chromosomal DNA characteristics comprises a sex chromosome content of the sperm cells.

4. The system as claimed in claim 3 , wherein the beam is focused by the optics system as a spot on the fluid stream at the first location, the spot having a generally elliptical shape with a length along a major axis extending at right angles to a direction of fluid stream flow and a width along a minor axis extending parallel to the direction of fluid stream flow, the width being less than a length of a head of a sperm cell passing through the beam spot.

5. The system as claimed in claim 4 , wherein the head of the sperm cell includes a DNA region having a length in the direction of stream flow, and wherein the beam spot width is less than the length of the DNA region.

6. The system as claimed in claim 5 , wherein the flow cytometry apparatus comprises a nozzle having an interior surface configured to exert a force on the cells tending to bring them into a desired orientation prior to passing through the beam.

7. The system as claimed in claim 6 , wherein the nozzle is rotatable about a longitudinal axis of the nozzle to adjust the desired cell orientation relative to the beam axis.

8. The system as claimed in claim 1 , wherein the optics system includes only one photodetector for detecting the emissions.

9. The system as claimed in claim 1 , wherein the flow cytometry apparatus comprises a nozzle having a nozzle orifice, and a capillary tube extending from the orifice through which the fluid stream is delivered to the first location.

10. The system as claimed in claim 9 , wherein the first location is inside the capillary tube.

11. The system as claimed in claim 10 , wherein the optics system is optically coupled to the capillary tube for transmission of the beam into the stream flowing through the tube.

12. The system as claimed in claim 1 , wherein the droplet generating system comprises a nozzle in communication with a piezoelectric transducer for producing an interference stream of droplets.

13. The system as claimed in claim 12 , wherein the droplet generating system further comprises one or more deflection plates for diverting droplets in the interference stream of droplets.

14. The system as claimed in claim 12 , wherein the interference stream is particle free.

15. A method of sorting cells according to chromosomal DNA characteristics comprising:

forming a fluid stream containing cells, wherein the fluid stream delivers the cells to a first location;

irradiating cells at the first location;

detecting emissions from irradiated cells, wherein said emissions include information indicative of the chromosomal DNA characteristics of the cells;

classifying cells in the fluid stream based on their chromosomal DNA characteristics;

selecting segments of the fluid stream based on the classification of cells contained therein;

forming a droplet interference stream wherein diverted droplets from the droplet interference stream hit the fluid stream thereby separating the selected segments and the cells contained therein from the fluid stream; and

diverting selected segments of the fluid stream with droplets from the droplet interference stream.

16. The method as claimed in claim 15 , wherein the cells are sperm cells and the DNA characteristics comprises a sex chromosome content of the sperm cells.

17. The method as claimed in claim 15 , wherein the step of classifying cells in the fluid stream based on their chromosomal DNA further comprises identifying X sperm cells and Y sperm cells.

18. The method as claimed in claim 17 , wherein the step of selecting segments further comprises sorting for X sperm and/or for Y sperm.