Patent ID: 7112444

Claim:
A method of performing a gradient-based assay in a microfluidic assay, comprising the steps of: providing a microfluidic device having a channel therethrough, the channel being partially defined by a channel wall extending along an axis; providing a plurality of biological targets axially spaced along the channel wall; introducing a stream of first fluid into the channel so as to flow therethrough, the first fluid stream having a predetermined concentration of particles therein; introducing a stream of second fluid into the channel so as to flow therethrough in laminar flow with the first fluid stream, the particles in the first fluid stream diffusing into the second fluid stream so as to cause a gradient of concentrations of particles in the second fluid stream such that predetermined concentrations of particles in the second stream intersect corresponding biological targets as the second fluid stream flows therepast; monitoring the plurality of biological targets for optical changes, the optical change of each biological target corresponding to the predetermined concentration of particles in the second fluid stream acting thereon; selecting one of the predetermined concentrations in response to the optical change of a user-selected biological target; and providing a plurality of wells spaced along the channel wall, wherein the plurality of biological targets are located within the wells.