Readout of diagnostic assays on a centrifugal microfluidic platform

This thesis presents the technical achievements towards establishing a <br>novel centrifugal microfluidic platform for multiplexed immunoassays <br>in the field of point-of-care applications. Multiplexing of immunoassays <br>is here defined as the detection of a set of different antigen <br>species from a given sample in a single channel. <br>Mixing as one of the crucial microfluidic unit operation is drastically <br>accelerated by two novel fluidic concepts. First, magnetic beads <br>confined in a mixing chamber are periodically deflected by a set of <br>permanent magnets aligned at spatially fixed positions. The resulting <br>relative motion of the beads with respect to the liquid induces advection. <br>In the second concept, without magnetic beads, the disk is spun with <br>periodic changes in the sense of rotation (shake-mode) where inertia <br>effects induce stirring of the liquids. As a result, both strategies speedup <br>mixing from about 10 minutes for mere diffusion to the 1-second <br>range. In several developed disk-based assays, shake-mode mixing <br>could proof to be a robust and versatile microfluidic tool. <br>Multiplexing of immunoassays on the centrifugal microfluidic platform <br>is technically implemented in two formats: as bead-based, or microarray- <br>based assays. <br>Bead-tagging in the multiplexed immunoassay scheme is implemented <br>by integrated quantum dots, or organic dyes. Here, a succesfully <br>implemented Hepatitis-A assay demonstrates the performance of the <br>approach with quantum dots as bead-tag. <br>A theoretical modeling of the bead-aggregation process in microfluidic <br>channels accompanied by experimental investigations resulted in a <br>microfluidic disk design, which allowed the successful conduction of <br>bead-based immunoassays. <br>Microarrays as an alternative to bead-based multiplexed immunoassays <br>are implemented and evaluated implementing a BSA assay on <br>the centrifugal microfluidic platform in three ways: on a rigid polymer <br>disk featuring microfluidic channels structures, on a PDMS lid, which <br>completely covers a lab-on-a-disk, or on a slide-based microfluidic chip <br>attached to a rotor (applied for patent). Beneficial in all cases are the <br>reduced sample and reagent consumption, the accelerated processing, <br>and the well controlled environmental settings along the complete <br>procedure. <br>The colorimetric absorbance readout as common scheme for metabolic <br>assays are implemented on the microfluidic centrifual system whereas <br>the optical path length through the detection cell as limiting factor is <br>drastically extended by monolithically incorporated V-grooves (applied <br>for patent). The performance of the simple and rugged concept is <br>successfully demonstrated on a modular setup to measure the concentration <br>of glucose (CV = 4%), hemoglobin (CV = 3%), and alcohol <br>(CV = 4%) in human whole blood. <br>The measurement of the hematocrit as an important marker for <br>medical diagnostics is transferred to the centrifugal microfluidic platform. <br>Here, a radially aligned dead end channel is first bubble-free <br>primed with blood. Here, trapping of gas upon priming is reliably <br>avoided by capillary wicking, which is solely promoted along <br>predetermined edges of the channel (applied for patent). After a <br>sedimentation step, the hematocrit is read out by visual inspection with <br>a disk-imprinted scale. As a result, an overall CV of 5% over the whole <br>physiological-pathological range is achieved. <br>A desktop-sized actuation and readout device for metabolic assays on <br>the centrifugal platform is conceptually designed; a demonstrator <br>device is assembled. <br>A designed and constructed test and development stand to accurately <br>visualize the propagation of fluids and the flow patterning in <br>micronchannels on fast spinning disks constitutes the experimental base <br>for this work and related ones.

Author dc:creator

• Grumann, Markus

Contributors dc:contributor

• Zengerle, Roland

• Mikrosystemtechnik
• Diagnostik
• zentrifugal
• blood
• centrifuga l, diagnostics
• disk

Repository record source_url

https://freidok.uni-freiburg.de/data/2272

OAI identifier oai:identifier

oai:freidok.uni-freiburg.de:2272