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.

Fluidic transport through nanochannels offers new opportunities to probe fundamental nanoscale transport phenomena and to develop tools for manipulating DNA, proteins, small molecules and nanoparticles. The small size of nanofabricated devices and the accompanying increase in the effect of surface forces, however, pose challenges in designing and fabricating flexible nanofluidic systems that can dynamically adjust their transport characteristics according to the handling needs of various molecules and nanoparticles. Here, we describe the use of nanoscale fracturing of oxidized poly(dimethylsiloxane) to conveniently fabricate nanofluidic systems with arrays of nanochannels that can actively manipulate nanofluidic transport through dynamic modulation of the channel cross-section. We present the design parameters for engineering material properties and channel geometry to achieve reversible nanochannel deformation using remarkably small forces. We demonstrate the versatility of the elastomeric nanochannels through tuneable sieving and trapping of nanoparticles, dynamic manipulation of the conformation of single DNA molecules and in situ photofabrication of movable polymeric nanostructures.

Photopatterning polymerization inhibition volumes by two-color irradiation enables exceptional 3D printing speed and functionality.

No abstract

We discovered that a protein concentration device can be constructed using a simple one-layer fabrication process. Microfluidic half-channels are molded using standard procedures in PDMS; the PDMS layer is reversibly bonded to a glass base such as a microscope slide. The microfluidic channels are chevron-shaped, in mirror image orientation, with their apexes designed to pass within approximately 20 microm of each other, forming a thin-walled section between the channels. When an electric field is applied across this thin-walled section, negatively charged proteins are observed to concentrate on the anode side of it. About 10(3)-10(6)-fold protein concentration was achieved in 30 min. Subsequent separation of two different concentrated proteins is easily achieved by switching the direction of the electric field in the direction parallel to the thin-walled section. We hypothesize that a nanoscale channel forms between the PDMS and the glass due to the weak, reversible bonding method. This hypothesis is supported by the observation that, when the PDMS and glass are irreversibly bonded, this phenomenon is not observed until a very high E-field was applied and dielectric breakdown of the PDMS is observed. We therefore suspect that the ion exclusion-enrichment effect caused by electrical double layer overlapping induces cationic selectivity of this nanochannel. This simple on-chip protein preconcentration and separation device could be a useful component in practically any PDMS-on-glass microfluidic device used for protein assays.

Photolithographic micromachining of silicon is a candidate technology for the construction of highthroughput DNA analysis devices. However, the development of complex silicon microfabricated systems has been hindered in part by the lack of a simple, versatile pumping method for integrating individual components. Here we describe a surface-tension-based pump able to move discrete nanoliter drops through enclosed channels using only local heating. This thermocapillary pump can accurately mix, measure, and divide drops by simple electronic control. In addition, we have constructed thermal-cycling chambers, gel electrophoresis channels, and radiolabeled DNA detectors that are compatible with the fabrication of thermocapillary pump channels. Since all of the components are made by conventional photolithographic techniques, they can be assembled into more complex integrated systems. The combination of pump and components into self-contained miniaturized devices may provide significant improvements in DNA analysis speed, portability, and cost. The potential of microfabricated systems lies in the low unit cost of silicon-based construction and in the efficient sample handling afforded by component integration.The recent rapid accumulation of genomic data for many organisms (1-3), together with the development of powerful DNA-based typing methods (4-6), has stimulated the demand for genetic information. The examination of the heritable components of common human diseases will involve population-based genetic studies and will require genetic typing of thousands of individuals at numerous genetic loci (7). To date, the labor-and material-intensive technologies for genetic typing have restrained its application to population analysis. Studies of large populations will benefit significantly from reductions in genotyping costs and improvements in equipment portability.DNA analysis using PCR-amplified polymorphism has become a general method for biological and clinical research. The biochemistry of the assay is robust and virtually identical for any genetic locus or source organism. Although well characterized, PCR analysis has not been assembled into a simple automated system. Standard PCR-based DNA typing involves (i) liquid handling of reagent and DNA template solutions, (ii) measurement of solution volumes, (iii) mixing of reagent and template, (iv) controlled thermal reaction of the mixture, (v) loading of the sample to an electrophoresis gel, and (vi) detection of DNA products. The complete process relies on human intervention at several stages to transfer liquids, mix reagents, track reaction vessels, and analyze results. In the ideal case, the processing steps would be merged into a single, integrated system composed of modular devices that are fully compatible and that function with minimal operator interaction.Although there are many formats, materials, and size scales for constructing integrated fluidic systems, silicon and glass microfabricated devices can provide a general solution. Silicon micromachining ...

An integrated microfluidic device capable of performing a variety of genetic assays has been developed as a step towards building systems for widespread dissemination. The device integrates fluidic and thermal components such as heaters, temperature sensors, and addressable valves to control two nanoliter reactors in series followed by an electrophoretic separation. This combination of components is suitable for a variety of genetic analyses. As an example, we have successfully identified sequence-specific hemagglutinin A subtype for the A/LA/1/87 strain of influenza virus. The device uses a compact design and mass production technologies, making it an attractive platform for a variety of widely disseminated applications.

Rayleigh-Benard convection is caused by buoyancy-driven instability in a confined fluid layer heated from below (1). The dimensionless Rayleigh number Ra = ga(T -T)h3/VK expresses the interplay between buoyant forces driving the instability and diffusive restoring forces acting in opposition. Here, a is the coefficient of thermal expansion of the fluid, g is the acceleration due to gravity, T, and T2 are the temperatures of the top and bottom surfaces of the cavity, respectively, h is the height of the cavity, v is the kinematic viscosity, and K is the thermal diffusivity.The inherent structure of Rayleigh-Benard convection-steady circulatory flow between surfaces maintained at two fixed temperaturesis ideally suited for performing thermally activated chemical reactions that require temperature cycling. We have developed a device that uses Rayleigh-Benard convection to perform polymerase chain reaction (PCR) amplification of DNA inside a 35-p1l cylindrical cavity. Instead of the external temperature control of conventional thermocyclers, temperature cycling is achieved as the flow field continually shuttles fluid packets vertically through the temperature zones associated with denaturation (-95?C) and annealing/extension (60? to 70?C). The steady circulatory flow field must engage the entire reaction volume yet be slow enough to allow the reaction within each temperature zone to reach completion. The parameters available to control the fluid motion are the Rayleigh number and the aspect ratio hid, where d is the diameter of the cavity. In the case of PCR, the required reaction efficiency constrains the reaction solution and the temperature difference; thus, Ra can only be changed by varying the height of the cavity, leaving geometry as the primary flow control parameter.