Methods and apparatus for separating live from dead organisms in a sample

A method comprising:

• providing, as input to a microfluidic passage of a microfluidic device, a fluid sample, wherein the microfluidic passage has at least one electrode system disposed adjacent to the microfluidic passage;
• generating, by at least one signal generator electrically connected to the at least one electrode system, at least one AC voltage to drive the at least one electrode system such that each electrode system of the at least one electrode system is driven by an AC voltage, wherein the at least one electrode system comprises a first electrode system and a second electrode system, and wherein generating at least one AC voltage comprises:
• generating a first AC voltage to drive the first electrode system, the first AC voltage having first characteristics that causes the first electrode system to selectively capture only the live organisms on the surface of at least one first electrode in the first electrode system by positive dielectrophoresis;
• and
• generating a second AC voltage to drive the second electrode system, the second AC voltage having second characteristics that causes the second electrode system to selectively capture only the dead organisms on the surface of at least one second electrode in the second electrode system by positive dielectrophoresis;
• imaging, by an optical system, the at least one first electrode while the live organisms are captured on the surface of the at least one first electrode to generate one or more first images;
• and
• processing, using a computer, the one or more first images to detect and/or quantify the live organisms in the one or more first images.