Genetic information is vital for understanding features and response of an organism. In humans, genetic errors are linked to the development of major diseases such as cancer and diabetes. In order to maximally exploit this information it is necessary to develop miniature sequencing assays that are rapid and inexpensive. In this paper we show how this could be attained with microfluidic chips that contain integrated assays. To date simple silicon/glass chips aimed for sequencing purpose have been realized; but these chips are not yet practical. Some of the solutions that are used to bring these devices closer to commercial applications are discussed.

This paper presents the design, fabrication, and testing of passive plastic microfluidic valves and active injectors driven by capillary forces. The passive valves stop the flow of a liquid inside a capillary using a capillary pressure barrier that develops when the channel cross section changes abruptly. Two types of valves with vertical and horizontal neck regions were fabricated yielding pressure barriers ranging from 1-6 kPa. Introducting asymmetry in the neck region, unidirectional valving action was achieved. The passive valving devices were used in combination with two electrodes to implement a sample injector. The injector uses an electrolytically-generated O-2 bubble that raises the liquid pressure beyond the barrier thus reestablishing flow with as little as 150 mu W Of electrical power.

This paper describes the fabrication and testing of plastic fluidic connectors suitable for the assembly of multichip microfluidic systems. The connectors basically consist of a series of 50-200 X 20 micrometers 2 capillaries embedded in a 70 micrometers -thick flexible polyimide substrate with large access holes ion both ends. The capillary walls and the connector exterior are coated with a thin layer of p- xylylene providing a high degree of chemical inertness and biocompatibility. These flexible connectors are inherently planar for ease of connection to flat substrates and are constructed using conventional batch lithographic techniques. The connector flow characteristics were tested in nitrogen gas and water. Multiple channel connectors with 3 and 5 capillaries 1.3-4.0 cm-long were constructed successfully.

The adhesion of polysilicon microstructures to their substrates is eliminated using a relatively conformal hydrophobic fluorocarbon (FC) coating grown in a field-free zone of a plasma reactor. Experiments show that the FC film deposition on top of the microstructure and on the underside was approximately 2:1. The FC coating is able to cover the entire underside of a 200 x 200 mu m(2) plate, with a 20% deposition nonuniformity. The coating exhibits a contact angle of 110 degrees and is able to prevent adhesion of cantilever beams and doubly supported beams to their substrates even after direct immersion in DI water. The durability of the coating was tested using an accelerated aging method, predicting a lifetime of greater than ten years at 150 degrees C. Periodic wear tests indicate that the coating remains hydrophobic even after 10(7) contact cycles.

Photolithographic micromachining of silicon is a candidate technology for the construction of high-throughput 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.

This paper reports the fabrication and testing of large-volume plastic capillaries and other fluidic components using a batch lithographic process. These components are fabricated on planar substrates using a simple three mask, low-temperature, IC compatible process that allows the integration of microfluidic and circuit elements. The microfluidic elements are conformal to the substrate thus overcoming the planarization required by bonded structures. In addition they have relatively large volumes in contrast to polysilicon based devices and are completely sealed in a batch manner overcoming the limitations of micromoulding. The capillaries are also optically transparent and can range from 0.5 /spl mu/m to 100 /spl mu/m in height. The fluidic components have been fabricated on top of regular silicon, glass, and polycarbonate wafers. Mechanical and biocompatibility tests indicate that the plastic components are suitable for DNA analysis instrumentation.