This paper describes a procedure that makes it possible to design and fabricate (including sealing) microfluidic systems in an elastomeric materialpoly(dimethylsiloxane) (PDMS)in less than 24 h. A network of microfluidic channels (with width >20 μm) is designed in a CAD program. This design is converted into a transparency by a high-resolution printer; this transparency is used as a mask in photolithography to create a master in positive relief photoresist. PDMS cast against the master yields a polymeric replica containing a network of channels. The surface of this replica, and that of a flat slab of PDMS, are oxidized in an oxygen plasma. These oxidized surfaces seal tightly and irreversibly when brought into conformal contact. Oxidized PDMS also seals irreversibly to other materials used in microfluidic systems, such as glass, silicon, silicon oxide, and oxidized polystyrene; a number of substrates for devices are, therefore, practical options. Oxidation of the PDMS has the additional advantage that it ...

Rapid prototyping of microfluidic systems in poly(dimethylsiloxane)

Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.

Fabrication of microfluidic systems in poly(dimethylsiloxane)

Following the trend towards smaller channel inner diameter for better separation performance and shorter channel length for shorter transport time, a modular construction of a miniaturized 'total chemical analysis system' is proposed. The theoretical performances of such systems based on flow injection analysis, chromatography and electrophoresis, are compared with those of existing chemical sensors and analysis systems.

Miniaturized total chemical analysis systems: A novel concept for chemical sensing

Single-crystal silicon is being increasingly employed in a variety of new commercial products not because of its well-established electronic properties, but rather because of its excellent mechanical properties. In addition, recent trends in the engineering literature indicate a growing interest in the use of silicon as a mechanical material with the ultimate goal of developing a broad range of inexpensive, batch-fabricated, high-performance sensors and transducers which are easily interfaced with the rapidly proliferating microprocessor. This review describes the advantages of employing silicon as a mechanical material, the relevant mechanical characteristics of silicon, and the processing techniques which are specific to micromechanical structures. Finally, the potentials of this new technology are illustrated by numerous detailed examples from the literature. It is clear that silicon will continue to be aggressively exploited in a wide variety of mechanical applications complementary to its traditional role as an electronic material. Furthermore, these multidisciplinary uses of silicon will significantly alter the way we think about all types of miniature mechanical devices and components.

Silicon as a mechanical material

A miniature gas analysis system has been built based on the principles of gas chromatography (GC). The major components are fabricated in silicon using photolithography and chemical etching techniques, which allows size reductions of nearly three orders of magnitude compared to conventional laboratory instruments. The chromatography system consists of a sample injection valve and a 1.5-m-long separating capillary column, which are fabricated on a substrate silicon wafer. The output thermal conductivity detector is separately batch fabricated and integrably mounted on the substrate wafer. The theory of gas chromatography has been used to optimize the performance of the sensor so that separations of gaseous hydrocarbon mixtures are performed in less than 10 s. The system is expected to find application in the areas of portable ambient air quality monitors, implanted biological experiments, and planetary probes.

S. C. Terry

Papers

A gas chromatographic air analyzer fabricated on a silicon wafer

A prototype gas analysis system using a miniature gas chromatograph