We have used a self-calibrating microfabricated capillary viscometer to analyze non-Newtonian power law fluids. The capillary viscometer can generate a wide range of shear rates during a single experimental run enabling quick and accurate analysis of non-Newtonian liquids. The measurement of viscosity is based on monitoring the capillary pressure-driven movement of fluid sample whose mean velocity and, therefore, shear rate varies with time. The device has been successfully tested for accuracy and robustness with dilute as well as semidilute solutions of flexible elastic polymers including poly(ethylene oxide) and hydrolyzed polyacrylamide to an aqueous solution of a stiff rodlike polymer molecule of xanthan gum, a popular emulsifier and food thickener, as well as with ink-jet printing inks. Viscosities in the range of 1-600 cP were measured, and shear rates varying from 5 to 1000 s(-1) have been obtained on the microfabricated viscometer with the current geometry and channel dimensions. The total measurement time varied between 2 and 8 min and less than 1 microL of sample volume was required. Such a microfabricated capillary viscometer would have possible applications in quality control and manufacturing where rapid and repeated measurements need to be made using limited sample volume.

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.

We have developed a microfabricated nanoliter capillary viscometer that quickly, easily, and inexpensively measures the viscosity of liquids. The measurement of viscosity is based on capillary pressure-driven flow inside microfluidic channels (depth approximately 30 microm and width approximately 300 microm). Accurate and precise viscosity measurements can be made in less than 100 s while using only 600 nL of liquid sample. The silicon-glass hybrid device (18 mm by 15 mm) contains on-chip components that measure the driving capillary pressure difference and the relevant geometrical parameters; these components make the nanoliter viscometer completely self-calibrating, robust, and easy to use. Several different microfabricated viscometers were tested using solutions with viscosities ranging from 1 to 5 cP, a range relevant to biological fluids (urine, blood, blood plasma, etc.). Blood plasma samples collected from patients with the symptoms of hyperviscosity syndrome were tested on the nanoliter capillary viscometer to an accuracy of 3%. Such self-calibrating nanoliter viscometers may have widespread applications in chemical, biological, and medical laboratories as well as in personal health care.

Pollution caused by the clean up of lithographic printing presses is a major problem faced by the printing industry. This paper explores alternate ink systems where the use of hydrocarbon solvents and volatile organic compounds (VOCs) for clean up is eliminated. The ink under consideration is a microemulsion, which can be emulsified in plain water–the property that can be used for its cleanup from presses. Furthermore, the washing is a completely physical process with no chemical reaction occurring thereby eliminating any salt streams. The ink washing commences in the form of tiny jets of water-soluble material vigorously coming out at the interface of the microemulsion ink drop and the wash liquid. Spontaneous emulsification is therefore proposed as the mechanism of washing. This paper discusses the ink formulation, its properties, and a model for spontaneous emulsification to explain its washing. The theoretical work is supported by experimental results.

We have developed a nanoliter viscometer that quickly, easily and inexpensively measures the viscosity of liquids. The measurement is based on capillary pressure driven flow inside microfabricated fluidic channels (depth similar to 30 mu m and width similar to 300 mu m). Accurate and precise viscosity measurements can be made in less than 100s while using only 600nl of liquid sample. The device measures 18mm by 15mm and has been successfully tested with viscosity standards, a non-newtonian liquid and with blood plasma. The device contains on-chip components that measure the capillary pressure and geometrical parameters; these components make the nanoliter viscometer self-calibrating, robust and easy to use. This microfabricated viscometer may have widespread applications in chemical, biological and medical laboratories as well as in personal health care.

We report initial steps towards development of microfluidic devices for detection and genotyping of influenza A viruses, by extending a design by Burns et al. [Science 282 (1998) 484] for human genotyping. Our first new device for influenza A genotyping carries out two reactions in series as well as an electrophoretic gel separation in a glass-silicon device around 3 cm wide and 10 cm long. Construction of the device utilizes solid-state electronics microfabricated in silicon and glass, deposition of resistive heaters for thermal cycling, a reaction chamber for restriction digestion, and a miniature gel separation column, with DNA driven by an electric field produced by miniature microfabricated electrodes. Detection of bands is by fluorescence, with an external light source; photodiode detectors can be either external or microfabricated into the device. The device is tested using restriction digestion on-chip and separating the products on an electrophoresis gel. The possible uses for devices of this type in tracking influenza variants, including H1, H3, H5, H9, and other subtypes, and in early recognition of emergence of variants with worldwide pandemic potential, are explored.

We demonstrate a versatile microfabricated electrophoresis platform, incorporating arrays of integrated on-chip electrodes, heaters, and temperature sensors. This design allows a range of different sieving gels to be used within the same device to perform separations involving both single- and double-stranded DNA over distances on the order of 1 cm. We use this device to compare linear and cross-linked polyacrylamide, agarose, and thermo-reversible Pluronic-F127 gels on the basis of gel casting ease, reusability, and overall separation performance using a 100 base pair double-stranded DNA ladder as a standard sample. While cross-linked polyacrylamide matrices provide consistently high-quality separations in our system over a wide range of DNA fragment sizes, Pluronic gels also offer compelling advantages in terms of the ability to remove and reload the gel. Agarose gels offer good separation performance, however, additional care must be exercised to ensure consistent gel properties as a consequence of the need for elevated gel loading temperatures. We also demonstrate the use of denaturing cross-linked polyacrylamide gels at concentrations up to 19% to separate single-stranded DNA fragments ranging in size from 18 to 400 bases in length. Primers differing by 4 bases at a read length of 30 bases can be separated with a resolution of 0.9-1.0 in under 20 min. This level of performance is sufficient to conduct a variety of genotyping assays including the rapid detection of single nucleotide polymorphisms (SNPs) in a microfabricated platform. The ability to use a single microelectrophoresis system to satisfy a wide range of separation applications offers molecular biologists an unprecedented level of flexibility in a portable and inexpensive format.