Microfabrication of a planar absorbance and fluorescence cell for integrated capillary electrophoresis devices

A micromachined absorbance and fluorescence detection cell for application to capillary electrophoresis within planar glass substrates (chips) is described. A microfabricated U-cell for absorbance provides a longitudinal path 120- 140 mu m long parallel to the now direction and gives at least a 10-fold increase in absorbance compared to an absorbance path transverse to the now direction. Absorbance detection limits of 0.003 AU gave similar to 6 mu M detection limits for hydrolyzed fluorescein isothiocyanate dye. The same device can be used for longitudinal fluorescence excitation with a 20-fold improvement in signal-to-background levels due to reduced scattering utilizing a form of sheath now. Fluorescence detection limits of similar to 20000 molecules and 3 nM were obtained for fluorescein.