Channel-specific coatings on microfabricated chips

This paper reports channel-specific immobilization of fluorescein-5-isothiocyanate (FITC)-labeled bovine serum albumin and β-galactosidase on microchips with a central channel and two crossing channels; referred to as a double cross channel configuration. Solvent wells at the termini of all channels were used to store reagents. Coatings were applied in multiple steps using electroosmotically driven flow to deliver reagents to specific channels in the chip. The first step in all coating reactions was derivatization of the capillary walls with an organosilane having a reactive pendant functional group. As the silylating reagent was transported from the reagent storage well to a specific waste well, capillary walls in the route of transport were silylated. Flow was maintained throughout a reaction. The route of transport, and thus the specificity of channel coating, were controlled by the well to which negative potential was applied. Flow in a multichannel network takes the shortest route between the electrodes delivering the motive potential. The second reagent in the reaction was delivered from a different well and took a different path through the channel network, as did other reagents. Only the channel being coated was in the flow path of all the reagents used in the coating process. The zone of immobilization in the case of FITC-labeled albumin was determined with confocal fluorescence microscopy. Enzyme activity of immobilized β-galactosidase (β-Gal) was monitored by following the hydrolysis of fluorescein mono-β-d-galactopyranoside to fluorescein with laser-induced fluorescence.