Patent ID: 7670471

Claim:
A method for detecting labeled molecules in a microfluidic device, said method comprising a) providing labeled molecules, wherein said molecules are labeled with a fluorescent dye; b) providing a microfluidic device comprising a channel microfabricated in a substrate, wherein said microfabricated channel comprises a detection region; c) transporting a solution comprising the labeled molecules through the microfluidic channel such that the molecules pass though the detection region, wherein said transporting does not comprise hydrodynamically focusing the solution with a sheath fluid; d) illuminating labeled molecules in the detection region with radiation from an excitation light source, wherein said radiation is of a wavelength that excites the fluorescent dye, and wherein the fluorescent dye when excited emits light of characteristic wavelengths; and e) detecting the emitted light, wherein labeled molecules outside the detection region are not illuminated with radiation from the excitation light source, and wherein, on average, only one labeled molecule occupies the detection region at a time.