Microfluidics Guided by Redox-Magnetohydrodynamics (MHD) for Lab-on-a-Chip Applications

Unique microfluidic control actuated by simply turning off and on microfabricated electrodes in a small-volume system was investigated for lab-on-a-chip applications. This was accomplished using a relatively new pumping technique of redox-magnetohydrodynamics (MHD), which as shown in this dissertation generated the important microfluidic features of flat flow profile and fluid circulation. MHD is driven by the body force, FB = j × B, which is the magnetic part of the Lorentz force equation, and its direction is given by the right hand rule. The ionic current density, j, was generated in an equimolar solution of potassium ferri/ferro cyanide by applying a constant current/potential across the gap between an anode-cathode pair of the electrodes. The magnetic field, B, was produced with an NdFeB permanent magnet beneath the chip. Two types of microelectrode geometries were used in this dissertation: microbands and concentric disks and rings. Horizontal flow profiles having uniform velocities (≤124.0 µm/s) at fixed heights across different gaps were sustained along a ~25.0 mm path using microband electrodes, in a small volume contained over an insulated silicon chip. Microfluidic rotational flow with velocity ≤ 14 µm/s was also achieved over an annular region between concentric disk (radius: 80 µm) and ring (inner radius: 800 µm) microelectrodes. In a different but related series of studies, natural convection generated by electrochemical processes was studied in a steady state microfluidic system, but without using redox-MHD convection. Natural convection was found to generate a maximum fluid velocity of \u3c 10 µm/s radially across the gap between concentric disk-ring microelectrodes. A proof-of-concept magnetic microbead enzyme assay was also integrated with the redox-MHD flat flow profile generated by [Ru(NH3)6]3+/2+ in Tris buffer. Selective placement of the assay complex at different locations combined with the uniform transport of the electroactive species by-product generated a strong current signal at the locations that were on the same flow path as the detector. When the assay complex was placed at other locations that were on parallel flow paths the current signal at the detector was insignificant (20%), thus confirming the potential of redox-MHD microfluidics to perform multiple, parallel assay detections

Redox-Magnetohydrodynamics, Flat Flow Profile-Guided Enzyme Assay Detection: Toward Multiple, Parallel Analyses

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 <i>p</i>-aminophenol, enzymatically generated at the bead-enzyme complex from its electroinactive precursor <i>p</i>-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

A review on applicability of naturally available adsorbents for the removal of hazardous dyes from aqueous waste

The effluent water of many industries, such as textiles, leather, paper, printing, cosmetics, etc., contains large amount of hazardous dyes. There is huge number of treatment processes as well as adsorbent which are available for the processing of this effluent water-containing dye content. The applicability of naturally available low cast and eco-friendly adsorbents, for the removal of hazardous dyes from aqueous waste by adsorption treatment, has been reviewed. In this review paper, we have provided a compiled list of low-cost, easily available, safe to handle, and easy-to-dispose-off adsorbents. These adsorbents have been classified into five different categories on the basis of their state of availability: (1) waste materials from agriculture and industry, (2) fruit waste, (3) plant waste, (4) natural inorganic materials, and (5) bioadsorbents. Some of the treated adsorbents have shown good adsorption capacities for methylene blue, congo red, crystal violet, rhodamine B, basic red, etc., but this adsorption process is highly pH dependent, and the pH of the medium plays an important role in the treatment process. Thus, in this review paper, we have made some efforts to discuss the role of pH in the treatment of wastewater