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Abstract

Microfluidic devices are provided for conducting fluid assays, for example biological assays, that have the ability to move fluids through multiple channels and pathways in a compact, efficient, and low cost manner. Discrete flow detection elements, preferably extremely short hollow flow elements, with length preferably less than 700 micron, preferably less than 500 micron, and internal diameter preferably of between about 50+/−25 micron, are provided with capture agent, and are inserted into microfluidic channels by tweezer or vacuum pick-and-place motions at fixed positions in which they are efficiently exposed to fluids for conducting assays. Close-field electrostatic attraction is employed to define the position of the elements and enable ready withdrawal of the placing instruments. The microfluidic devices feature flow elements, channels, valves, and on-board pumps that are low cost to fabricate accurately, are minimally invasive to the fluid path and when implemented for the purpose, can produce multiplex assays on a single portable assay cartridge (chip) that have low coefficients of variation. Novel methods of construction, assembly and use of these features are presented, including co-valent bonding of selected regions of faces of surface-activatable bondable materials, such as PDMS to PDMS and PDMS to glass, while contiguous portions of one flexible sheet completes and seals flow channels, fixes the position of inserted analyte-detection elements in the channels, especially short hollow flow elements through which sample and reagent flow, and other portions form flexible valve membranes and diaphragms of pumps. A repeated make-and-break-contact manufacturing protocol prevents such bonding to interfere with moving the integral valve diaphragm portions from their valve seats defined by the opposed sheet member, which the flexible sheet material engages. Preparation of two subassemblies, each having a backing of relatively rigid material, followed by their assembly face-to-face in a permanent bond is shown. Hollow detection flow elements are shown fixed in channels, that provide by-pass flow paths of at least 50% of the flow capacity through the elements; in preferred implementations, as much as 100% or more. Metallized polyester film is shown to have numerous configurations and advantages in non-permanently bonded constructions. A method of preparing detection elements for an assay comprises batch coating detection elements, or hollow flow elements by mixing and picking and placing the elements in flow channels of a microfluidic device, capturing the flow elements by bonding two opposed layers while sealing the flow channels.

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