Cell processing using magnetic particles

A method of processing sperm cells comprising the steps of:

• a) forming a stream comprising the sperm cells;
• b) determining whether a property of interest is present or absent in the sperm cells in the stream;
• c) ablating or photodamaging a subpopulation of the sperm cells based on the presence or absence of the property of interest in the sperm cells;
• d) collecting the sperm cells;
• e) adding magnetic particles to the collected sperm cells to form a mixture, the magnetic particles having a diameter of 30 to 1000 nm and comprising a chargeable silicon-containing compound, the magnetic particles binding to the ablated or photodamaged subpopulation of sperm cells solely through an electrical charge interaction;
• f) applying a magnetic field to the magnetic particle-bound sperm cells;
• and
• g) removing the magnetic particle-bound subpopulation from the mixture.