Redox-Magnetohydrodynamic Microfluidics Without Channels and Compatible with Electrochemical Detection Under Immunoassay Conditions

Abstract

A unique capability of redox-magnetohydrodynamics (redox-MHD) for handling liquids on a small scale was demonstrated. A 1.2-μL solution plug was pumped from an injection site to a detector without the need for a channel to direct the flow. The redox pumping species did not interfere with enzymatic activity in a solution compatible with enzyme-linked immunoassays. Alkaline phosphatase (AP), a common enzyme label, converted p-aminophenyl phosphate (PAPP) to p-aminophenol (PAPR) in the presence of 2.5 mM Ru(NH3)6Cl2 and 2.5 mM Ru(NH3)6 Cl3, in 0.1 M Tris buffer (pH=9). A solution plug containing PAPP (no AP) was pumped through the surrounding solution containing AP (no PAPP), and the enzymatically-generated PAPR was easily detected and distinguishable electrochemically from the pumping species with square wave voltammetry down to 0.1 mM concentrations. The test device consisted of a silicon chip containing individually-addressable microband electrodes, placed on a 0.5-T NdFeB permanent magnet with the field oriented perpendicular to the chip. A 8.0-mm wide × 15.5-mm long × 1.5-mm high volume of solution was contained by a poly(dimethylsiloxane) gasket and capped with a glass slide. A steady-state fluid velocity of ~30 μm/s was generated in a reinforcing flow configuration between oppositely polarized sets of pumping electrodes with ~2.1 μA.

A Multi-Pump Magnetohydrodynamics Lab-On-A-Chip Device for Automated Flow Control and Analyte Delivery

“…The criterion for choosing wider channels and a high current throughput involves evaluating the possibility of using an MHD pump on a microfluidic system. Figure 3A shows a summary of the results obtained with three different chips, designed to investigate the effect of the channel widths (0.85, 1.54, and 1.75 mm) and applied potentials (10,15,20,25, and 30 V) on the flow rate. These experiments were performed using 0.5 mol L −1 NaH 2 PO 4 as the background electrolyte and measuring the time required for a drop of methylene blue (10 µL/0.2 g L −1 ) solution to move through the channel (69 mm in length).…”

“…For stirring purposes, Bau et al developed an MHD stirrer that exhibits chaotic advection with individual electrodes positioned along its opposing walls [ 18 ]. Fritsch et al pioneered several MHD-based devices for fluid handling, such as an MHD-driven flow using redox species [ 19 , 20 , 21 ]. Recent advances of this research group have focused on lab-on-a-chip devices that are able to handle fluids without sidewall channels, without bubble generation, and without the need to use redox species [ 22 , 23 ].…”

Combining magnetic forces for contactless manipulation of fluids in microelectrode-microfluidic systems

“…As it does not need any moving parts, it allows flexibility in device design. It offers multidirectional and channel-less fluid flow 19 and compatibility with both aqueous and non-aqueous solutions. The electrode reactions can also produce gradients of mass density and electrical conductivity 26 that result in additional forces which may further influence the fluid flow.…”

Preliminary Study on Planar Electromagnetic Microfluidics Based a Microsensor by Finite Element Analysis

“…MHD micropumps have been investigated by Jang and Lee [26], Lemoff and Lee [27], Huang et al [28], Bau et al [29], [30] and other researchers in the microfluidics research. Weston et al proposed redox-magnetohydrodynamic microflu-idics for flow control and applied them in electrochemical sensing under immunoassay conditions [31].…”