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.

Fragments of exogenous DNA that range in size up to several hundred kilobase pairs have been cloned into yeast by ligating them to vector sequences that allow their propagation as linear artificial chromosomes. Individual clones of yeast and human DNA that have been analyzed by pulsed-field gel electrophoresis appear to represent faithful replicas of the source DNA. The efficiency with which clones can be generated is high enough to allow the construction of comprehensive libraries from the genomes of higher organisms. By offering a tenfold increase in the size of the DNA molecules that can be cloned into a microbial host, this system addresses a major gap in existing experimental methods for analyzing complex DNA sources.

H3Africa is developing capacity for health-related genomics research in Africa

No abstract

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 ...