A device was developed that uses microfabricated fluidic channels, heaters, temperature sensors, and fluorescence detectors to analyze nanoliter-size DNA samples. The device is capable of measuring aqueous reagent and DNA-containing solutions, mixing the solutions together, amplifying or digesting the DNA to form discrete products, and separating and detecting those products. No external lenses, heaters, or mechanical pumps are necessary for complete sample processing and analysis. Because all of the components are made using conventional photolithographic production techniques, they operate as a single closed system. The components have the potential for assembly into complex, low-power, integrated analysis systems at low unit cost. The availability of portable, reliable instruments may facilitate the use of DNA analysis in applications such as rapid medical diagnostics and point-of-use agricultural testing.

Nanoliter-sized liquid drops can be accurately metered inside hydrophilic microchannels using a combination of hydrophobic surface treatment and air pressure. The technique involves spontaneously filling the microchannels up to a hydrophobic region and splitting a liquid drop by injecting air through a hydrophobic side channel. The hydrophobic regions are fabricated by using a patterned metal mask on a substrate. The patterned substrate is immersed in an isooctane solution containing 1H,1H,2H,2H-per-fluorodecyltrichlorosilane to form hydrophobic patches on the exposed surface. Stripping the metal mask leaves the hydrophobic patches and restores the hydrophilic substrate surface. Precise and accurate liquid volumes, ranging from 0.5 to 125 nanoliters, have been metered using this technique. Theoretical predictions of the pressure needed to meter drops compare well with the experimental values.

Fast solute mixing can be achieved in a microchannel by rapid unidirectional displacement of a discrete liquid drop. The recirculation streamlines created within the liquid during the drop's motion cause the solute to interlayer across the channel depth, provided the interlayer diffusion of the solute is small. Uniform interlayering appears when the drop is displaced by more than three drop lengths in a slit-type microchannel, thereby reducing the solute diffusion distances to a fraction of the channel depth. By fabricating the microchannel to a depth of less than 50 µm even large molecules with a low diffusivity (D < 10 −8 cm 2 s −1) can be mixed in seconds. The above strategy is shown by modeling the mixing of solutes present in a drop moving in a slit-type microchannel.

A modeling approach is developed to account for the important effects of intermicellar exchange on the ultrafine particle formation in reverse micelles. A set of fusion-fission schemes is specifically proposed and used for modeling intermicellar metal exchange. The dynamic effects largely differing in their time scales are decoupled using a two-staged approach. Growth of metal particles is simulated to occur through intramicellar attachment of free metal atoms from an instantaneous reduction reaction and as well as by transfer and attachment through intermicellar exchange. Simulation results predict increase in particle size with aqueous core size and total aqueous phase volume, increase in particle number density with surfactant concentration at fixed aqueous phase to surfactant molar ratio, a minimum in average particle size as a function of salt concentration, and increase in particle size polydispersity with salt concentration and aqueous core size. Low values of the order of 10 -1 are found for the number ratio of particles to micelles. All these effects have been observed experimentally. The mean core size and the critical metal nucleation number are found to be the primary influencing parameters for the final particle sizes. It is further found that the polydispersity can be controlled through proper choice of starting mixture conditions.

Circulating tumor cells (CTCs) have been shown in many studies as a possible biomarker for metastasis and may be instrumental for the spread of the disease. Despite advances in CTC capturing technologies, the low frequency of CTCs in cancer patients and the heterogeneity of the CTCs have limited the wide application of the technology in clinic. In this study, we investigated a novel microfluidic technology that uses a size- and deformability-based capture system to characterize CTCs. This unique platform not only allows flexibility in the selection of antibody markers but also segregates the CTCs in their own chambers, thus, enabling morphological, immunological and genetic characterization of each CTC at the single cell level. In this study, different breast cancer cell lines including MCF7, MDA-MB-231 and SKBR3, as well as a panel of breast cancer biomarkers were used to test the device. The technology can capture a wide range of cells with high reproducibility. The capturing efficiency of the cells is greater than 80%. In addition, the background of leukocytes is minimized because individual cells are segregated in their own chambers. The device captured both epithelial cancer cells such as MCF7 and SKBR3 and mesenchymal cells such as MDA-MB-231. Immunostaining of the captured cells on the microchannel device suggests that a panel of breast cancer biomarkers can be used to further characterize differential expression of the captured cells.