Microfluidic chip for biochemical reaction and electrophoretic separation by quantitative volume control

We have developed a microfluidic integrated chip with all the fluidic manipulations required for biochemical reaction and electrophoretic separation. The microchip was fabricated using standard photolithography, isotropic wet etching, liftoff patterning of fluorocarbon film, and polydimethylsiloxane replica molding. The fabricated microfluidic chip (46 mm × 25 mm) was composed of two nanoliter-metering microchannel networks, a serpentine mixing channel, a sample injector, and an electrophoretic separation channel. In particular, a novel Y-shaped sample injector was developed as an important interface for the successful combination of the biochemical reaction with electrophoretic separation. A nanoliter-sized sample was pneumatically injected into the separation channel using the novel Y-shaped sample injector. This consisted of a planar hydrophobic valve and two vertical hydrophobic valves. The performance of the hydrophobic valves for fluidic manipulations was predicted using capillary pressure derived from the relationship of the work performed by the capillary pressure (dUp), the surface free energy of the system (dUs), and Young's equation. In addition, we were able to explain in detail the fluidic manipulation schemes for the biochemical reaction and subsequent separation. We also successfully demonstrated the enzyme reaction of β-galactosidase using fluorescein di-β-d-galactopyranoside as a substrate and the electrophoretic separation of its reaction products.