Biochemical analysis with microfluidic systems

Abstract

Microfluidic systems are capillary networks of varying complexity fabricated originally in silicon, but nowadays in glass and polymeric substrates. Flow of liquid is mainly controlled by use of electroosmotic effects, i.e. application of electric fields, in addition to pressurized flow, i.e. application of pressure or vacuum. Because electroosmotic flow rates depend on the charge densities on the walls of capillaries, they are influenced by substrate material, fabrication processes, surface pretreatment procedures, and buffer additives. Microfluidic systems combine the properties of capillary electrophoretic systems and flow-through analytical systems, and thus biochemical analytical assays have been developed utilizing and integrating both aspects. Proteins, peptides, and nucleic acids can be separated because of their different electrophoretic mobility; detection is achieved with fluorescence detectors. For protein analysis, in particular, interfaces between microfluidic chips and mass spectrometers were developed. Further levels of integration of required sample-treatment steps were achieved by integration of protein digestion by immobilized trypsin and amplification of nucleic acids by the polymerase chain reaction. Kinetic constants of enzyme reactions were determined by adjusting different degrees of dilution of enzyme substrates or inhibitors within a single chip utilizing mainly the properties of controlled dosing and mixing liquids within a chip. For analysis of kinase reactions, however, a combination of a reaction step (enzyme with substrate and inhibitor) and a separation step (enzyme substrate and reaction product) was required. Microfluidic chips also enable separation of analytes from sample matrix constituents, which can interfere with quantitative determination, if they have different electrophoretic mobilities. In addition to analysis of nucleic acids and enzymes, immunoassays are the third group of analytical assays performed in microfluidic chips. They utilize either affinity capillary electrophoresis as a homogeneous assay format, or immobilized antigens or antibodies in heterogeneous assays with serial supply of reagents and washing solutions.

Capillary electrophoresis of proteins 2003–2005

“…CE on microchip is a promising technology since it offers an easy integration of many steps including sample preparation, derivatization, and coupling of several separation procedures together [175,176].…”

Multiphysical Modeling of DC and AC Electroosmosis in Micro- and Nanosystems

“…The DC electroosmotic pumps are widely exploited in experimental and commercial microfluidic devices, e.g., see reviews (Becker & Locascio, 2002, Beebe et al, 2002, Bilitewski et al, 2003, Chang & Yang, 2007, Laser & Santiago, 2004. The reaction transport processes in such devices have been also modeled and analyzed, e.g., (Erickson, 2005, He & Hauan, 2006, Postler et al, 2008.…”

CE methods for the determination of non‐protein amino acids in foods

“…Electrophoresis on microchips (usually named as chip or microchip electrophoresis) is a promising technology since it offers an easy integration of many steps including sample preparation, derivatization, and coupling of several separation procedures together [37,38]. In addition, the use of microchips instead conventional CE systems leads to reduced analysis times.…”