Microfabrication and characterization of Teflon AF-coated liquid core waveguide channels in silicon

The fabrication and testing of Teflon AF-coated channels on silicon and bonding of the same to a similarly coated glass wafer are described. With water or aqueous solutions in such channels, the channels exhibit much better light conduction ability than similar uncoated channels. Although the loss is greater than extruded Teflon AF tubes, light throughput is far superior to channels described in the literature consisting of [110] planes in silicon with 45degrees sidewalls. Absorbance noise levels under actual flow conditions using an LED source, an inexpensive photodiode and a simple operational amplifier circuitry Was 1 x 10(-4) absorbance units over a 10-mm path length (channel 0.17-mm deep x 0.49-mm wide), comparable to many commercially available macroscale flow-through absorbance detectors. Adherence to Beer's law was tested over a 50-fold concentration range of an injected dye, with the linear r(2) relating the concentration to the observed absorbance being 0.9993. Fluorescence detection was tested with fluorescein as the test solute, a high brightness blue LED as the excitation source and an inexpensive miniature PMT. The concentration detection limit was 3 x 10(-9) M and the corresponding mass detection limit was estimated to be 5 x 10 (-16) mol.