Investigations of Immunoassay-Compatible Species for Microfluidic Pumping with Redox Magnetohydrodynamics

by Hooten, Christena; Weston, Melissa C.; Fritsch, Ingrid

Microfluidics is important in the automation of multi-step immunoassays on a chip, which could lead toward simplified instrumentation and anal. of many biochem. substances. We have been investigating a relatively new approach to microfluidics, involving redox-MHDs (MHD). We will report studies toward making this pumping method compatible with immunoassay components, so that lab-on-a-chip devices with redox-MHD will be possible. Redox MHD has features that complement other fluid-pumping methods and could fill a niche, such as with its ability to operate under both aq. and non-aq. conditions and the ease of switching flow direction. In redox MHD, ions generated from oxidn. and redn. of redox species, and moving at right angles to a magnetic field experience a force in the direction of the cross product, transferring momentum to surrounding mols., and causing flow in that direction. If handheld devices are developed for redox-MHD microfluidics, then permanent magnets are likely to be used that have a low magnetic flux d. (<1 T). So, there is concern that high redox concns. will be necessary to produce sufficient fluid flow, and that subsequent reactions with or inactivity of the antibodies and enzymes involved in an immunoassay would be problematic. We used the activity of alk. phosphatase, a common enzyme label in electrochem. immunoassays, with the substrate, p-aminophenylphosphate (PAPP), to evaluate compatibility with different redox species and varied concns. The corresponding velocity from redox MHD under these conditions was detd. by tracking the position of 10-µm polystyrene beads using a digital-video-camera attached to a microscope.