Chemical applications of microfluidics

Microfluidics, comprising the design, fabrication, and optimization of microfluidic devices, has successfully transformed numerous chemical and biological technologies from macroscale to microscale. Microfluidic devices comprise microscale structures such as channels with typical dimensions from microns to millimeters; thus microfluidic devices manipulate fluid volumes at nanoliter or microliter levels. We have explored the chemical applications of microfluidics by developing innovative fabrication techniques for making microfluidic devices and demonstrating their capabilities.; We have designed and fabricated a polydimethylsiloxane (PDMS) microfluidic device as a platform for coupling capillary electrophoresis (CE) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS). The coupling is advantageous because CE has the power to separate analytes of a sample and MALDI-MS provides accurate and sensitive mass-to-charge characterization of the analytes. In this particular microfluidic device, the coupling is realized by the fractionation of the separated analytes. The fractions are collected in open reservoirs, and the contents of these reservoirs are then mixed with a matrix solution and deposited on a MALDI-MS sample plate for subsequent MALDI-MS analysis. The fractionation carried out in the microfluidic device is essential to overcome the difficulty of interfacing CE separation with MALDI-MS sample preparation. Using this microfluidic device, mixtures of peptides are first separated by CE and then analyzed by MALDI-MS, thereby constructing a two-step characterization of each sample.; We have designed and fabricated a PDMS microfluidic device containing an array of gold spots which provides a platform for carrying out heterogeneous-phase biochemical assays including immunoassays and nucleic acid hybridization assays. Surface plasmon resonance (SPR) imaging is used to monitor the immunoreactions and nucleic acid hybridization reactions. This combination offers two significant advantages: (1) the microfluidic device dramatically reduces reaction time and sample consumption; and (2) the SPR imaging yields real-time detection of the formation of immunocomplexes or hybridized complexes. Using the combined system of microfluidic device and SPR imaging readout, an immunoassay and a nucleic acid hybridization assay are performed in a shorter time compared to traditional assays, and adequate sensitivity is obtained in measurements.; We have developed a method for surface modification of PDMS microfluidic devices. The electroosmotic flow (EOF) in a PDMS separation channel can be enhanced and controlled by adding a carboxylic acid to the prepolymer prior to curing. Because this modification does not significantly change the lipophilicity of the PDMS surface, it is possible to combine the modified PDMS with a dynamic coating of dodecyl-beta-D-maltoside (DDM). The combination of the surface modification and the dynamic coating of DDM is an effective means for both providing stable EOF in the PDMS channels and preventing protein adsorption on the channel walls, which facilitates non-denaturing electrophoretic separation of proteins in a PDMS microfluidic device.; We have also developed a method for making layer-to-layer interconnections in PDMS microfluidic devices. Thin perforated PDMS membranes (∼50 mum) are bonded to thicker PDMS slabs (1 mm or more) by means of thermally cured PDMS prepolymer to form a three-dimensional (3D) channel structure, which may contain channel or valve arrays that can pass over one another. Devices containing as many as two slabs and three perforated membranes are demonstrated. By this means, we created 3D PDMS microfluidic devices for display and for liquid dispensing.