Absorbance cell for microfluid devices

An improved absorbance or detection cell for a microfluid device, and in accordance with an aspect of the invention, the absorbance cell comprises a bottom plate having a channel bearing surface in which a channel having a fluid inlet and fluid outlet is defined, a top plate having a channel facing surface bound to the channel bearing surface of the bottom plate and first and second reflecting elements formed on opposed sides of the channel to form a waveguide through which the channel extends such that radiation propagating along the waveguide makes multiple passes across the channel, the waveguide having a radiation input end and a radiation output end.