Monolithic integration of optical waveguides for absorbance detection in microfabricated electrophoresis devices

The fabrication and performance of an electrophoretic separation chip with integrated optical waveguides for absorption detection is presented. The device was fabricated on a silicon substrate by standard microfabrication techniques with the use of two photolithographic mask steps. The waveguides on the device were connected to optical fibers, which enabled alignment free operation due to the absence of free-space optics. A 750 microm long U-shaped detection cell was used to facilitate longitudinal absorption detection. To minimize geometrically induced band broadening at the turn in the U-cell, tapering of the separation channel from a width of 120 down to 30 microm was employed. Electrical insulation was achieved by a 13 microm thermally grown silicon dioxide between the silicon substrate and the channels. The breakdown voltage during operation of the chip was measured to 10.6 kV. A separation of 3.2 microM rhodamine 110, 8 microM 2,7-dichlorofluorescein, 10 microM fluorescein and 18 microM 5-carboxyfluorescein was demonstrated on the device using the detection cell for absorption measurements at 488 nm.