R&D – The researchers built a device in which an extremely narrow plastic tube rests on a silicon substrate. A wire is connected to a single point beneath the tube. An extremely small current is run through the wire, both generating heat that radiates into the tube and measuring the temperature of the tube and its contents.
When a solution containing microscopic particles is injected into the tube it flows past the wire and the heated area. When the particles pass through this thermal zone they alter the electrical resistance of the wire.
Since the researchers know the flow rate of the solution through the tube, they can measure the length of time that the electrical resistance was changed and calculate the size of the objects suspended in the solution. more> http://tinyurl.com/q4f98hd