title: Redox-magnetohydrodynamics, flat flow profile-guided enzyme assay detection: toward multiple, parallel analyses.
abstract: A proof-of-concept superparamagnetic microbead-enzyme complex was integrated with microfluidics pumped by redox-magneto-hydrodynamics (MHD) to take advantage of the magnet (0.56 T) beneath the chip and the uniform flat flow profile, as a first step toward developing multiple, parallel chemical analyses on a chip without the need for independent channels. The superparamagnetic beads were derivatized with alkaline phosphatase (a common enzyme label for biochemical assays) and magnetically immobilized at three different locations on the chip with one directly on the path to the detector and the other two locations adjacent to, but off the path, by a distance >5 times the detector diameter. Electroactive p-aminophenol, enzymatically generated at the bead-enzyme complex from its electroinactive precursor p-aminophenyl phosphate in a solution containing a redox species [Ru(NH3)6](3+/2+) for pumping and Tris buffer, was transported by redox-MHD and detected with square wave voltammetry at a 312 μm diameter gold microdisk stationed 2 mm downstream from the bead-complex on the flow path. Oppositely biased pumping electrodes, consisting of 2.5 cm long gold bands and separated by 5.6 mm, flanked the active flow region containing the bead-enzyme complex and detection site. The signal from adjacent paths was only 20% of that for the direct path and ≤8% when pumping electrodes were inactive.
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas , Fayetteville, Arkansas 72701, United States.
authors.forename: Vishal
authors.initials: V
authors.lastname: Sahore
authors.forename: Ingrid
authors.initials: I
authors.lastname: Fritsch
mesh_terms: D000469:Alkaline Phosphatase / Q000737:chemistry; D000627:Aminophenols / Q000737:chemistry; D000818:Animals; D055664:Electrochemical Techniques / Q000295:instrumentation / Q000379:methods*; D004798:Enzymes / Q000032:analysis*; D004800:Enzymes, Immobilized / Q000737:chemistry; D006801:Humans; D057446:Hydrodynamics; D008280:Magnetics / Q000295:instrumentation / Q000379:methods*; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D010084:Oxidation-Reduction; D017975:Ruthenium Compounds / Q000737:chemistry; D014325:Tromethamine
chemical_list: D000627:Aminophenols; D004798:Enzymes; D004800:Enzymes, Immobilized; D017975:Ruthenium Compounds; D014325:Tromethamine; C031584:hexammineruthenium; D000469:Alkaline Phosphatase; C026729:4-aminophenol