High-Pressure Microfluidic Systems for Protein and Cell Analysis

Miniaturization of bioanalytical devices is of intense interest for counteracting bioterrorism, enhancing drug discovery, and speeding biochemical research. Microchip-based analytical techniques have allowed increases in the complexity of microanalytical systems, primarily through the development of more sophisticated geometries.

Since numerous crucial analysis and synthesis techniques (e.g., liquid chromatography, surface catalysis) depend on interaction of liquid-phase molecules with a solid substrate, maximum process efficiencies are achieved through maximization of surface area. Nanoporous matrices can be used to maximize surface area, but high pressures (>300 bar) are often required to move liquid samples through these matrices at optimal flow rates.

We present techniques for sophisticated control of high-pressure liquids on microchips, which enable the process efficiencies associated with high-pressure flow through nanoporous matrices to be combined with more complicated geometries and analysis techniques associated with microchips. The new configurations enabled by these techniques create new capabilities for manipulation of biological samples in microanalytical systems.

We will first present techniques for generating high-pressure flow on chip. Electroosmotic forces on charged nanoporous surfaces in contact with liquids can be used to generate high pressures in microfluidic systems; we will discuss fabrication and optimization techniques. Second, we will present novel techniques for high-pressure (10-300 bar) microfluidic control. In-situ laser-induced polymerization is used to fabricate free-standing mobile polymer elements inside silica microchannels, whose actuation (actively voltage-addressed or passive) can be used to rout high pressure flows for chemical synthesis or chromatography. Application of these flow control elements is demonstrated in an integrated microchip high-pressure liquid chromatography system that can analyze 200 pl samples and has performed simple protein separations in 40 s. Facile high-pressure analysis of such small volumes enables the contents of cells to be analyzed without dilution.