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SUMMARYThis paper presents a micro device employing the Coulter principle for counting and sizing of living cells and particles in liquid suspension. The microchip Coulter Particle Counter (pCPC) has been employed into a planar silicon structure covered with glass, which enables detailed observation during operation possible. By sheathing of a non-conductive liquid on either side of an electrolyte, it is possible to optimize the sensitivity to a specific cell-size dynamically. A method for measuring the relative flow-rates between liquid phases with different conductivity is presented. The method utilizes the laminar flow and short contact time of liquids in microchannels. As a result, the width of the liquids can be controlled without knowing the actual flow rates. The pCPC have been fabricated by standard microfabrication techniques, including NE, wet silicon etching, metalization and anodic bonding. The manufacturing is compatible with the fabrication of many different devices such as particle sorters and mixers.

A simple coaxial jet mixer for rapid and efficient confluent mixing under laminar flow conditions (Re < 5) is described. This device demonstrates exceptional control of mixing between two laminar streams by creating shear forces due to variable flow velocities at the point of confluence. It is suitable for flow injection and cytometric analyses of rapid kinetic events which require contact mixing of two solutions and subsecond measurements of the evolving reaction. This apparatus was devised for flow injection cytometry as performed on a Becton Dickinson FACS Analyzer. Under normal cytometric conditions and at a sample introduction rate of 60 microL/min, the laminar jet mixer is capable of complete mixing of two solutions within 55 ms. Kinetic measurements can be performed on the FACS Analyzer in a variable time range of 100 ms to 3 min with 14-30 ms temporal resolution of the studied event. Since no boost in core flow is required, potential spectral distortions due to core flow variations are eliminated. This coaxial jet mixer can be easily constructed and employed on a variety of cytometers as well as conventional flow injection analysis systems, since it is an effective mixer under most flow conditions.

Background: Use of microfluidics in point-of-care testing (POCT) will require on-board fluidics, self-contained reagents, and multistep reactions, all at a low cost. Disposable microchips were studied as a potential POCT platform. Methods: Micron-sized structures and capillaries were embedded in disposable plastics with mechanisms for fluidic control, metering, specimen application, separation, and mixing of nanoliter to microliter volumes. Designs allowed dry reagents to be on separate substrates and liquid reagents to be added. Control of surface energy to ؎5 dyne/cm 2 and mechanical tolerances to <1 m were used to control flow propulsion into adsorptive, chromatographic, and capillary zones. Fluidic mechanisms were combined into working examples for urinalysis, blood glucose, and hemoglobin A 1c testing using indicators (substances that react with analyte, such as dyes, enzyme substrates, and diazonium salts), catalytic reactions, and antibodies as recognition components. Optical signal generation characterized fluid flow and allowed detection. Results: We produced chips that included capillary geometries from 10 to 200 m with geometries for stopping and starting the flow of blood, urine, or buffer; vented chambers for metering and splitting 100 nL to 30 L; specimen inlets for bubble-free specimen entry and containment; capillary manifolds for mixing; microstructure interfaces for homogeneous transfer into separation membranes; miniaturized containers for liquid storage and release; and moisture vapor barrier seals for