The 2014 Colin G. Fink Summer Research Fellowship -- Summary Report: Advanced Microfluidic Pumping at Poly(3,4-ethylenedioxythiophene)-Modified Electrodes via AC-Magnetohydrodynamics

Abstract

A p aradigm shift in microfluidic pumping using redox-magnetohydrodynamics (MHD) that preserves its advantages and resolves problems that previously slowed its application in analytical chemistry (for pumping small volumes and sustaining fluid flow) is demonstrated herein. Miniaturization of chemical analysis for labon-a-chip (LOAC) devices offers portability and automation with less power, reagent and waste volumes, and analysis time. A crucial feature is the programmable manipulation of fluid within the device. MHD microfluidics Fig. 1. (a) Photograph of the microelectrode array chip showing electrode features and dimensions. Expanded images show unmodified gold and PEDOT-modified gold band electrodes as viewed under a microscope. During the AC MHD experiments, electrode set 1 (working), and sets 2 and 3 (combined auxiliary/quasi-reference) were active. Set 1 was oppositely biased from sets 2 and 3. (b) Fluid flow profile based on bead speeds in the 5600 µm gap between PEDOT-modified microband electrodes. Error bars represent ± one standard deviation. (c) Particle image velocimetry (PIV) data from which points in (b) were obtained. (d) Vectors involved in AC-MHD for synchronized electrical and magnetic fields to maintain flow in a single direction.can provide continuous pumping without channels or moving parts and can stop or reverse fluid flow without the need for valves by switching off or changing the sign of the ionic current, respectively. 1 The magnetohydrodynamic force, F B (N•m −3 ), and therefore fluid flow, is generated by the ionic current density, j (C•s −1 •m −2 ), when perpendicular to a magnetic field, B (T), and follows the right-hand rule according to the cross-product relationship, F B = j × B. [2][3][4][5] In previous studies, we have shown that electrodes modified with poly(3,4-ethylenedioxythiophene) (PEDOT) are capable of high currents while limiting the interaction with the sample, thus improving compatibility. However, use of PEDOTmodified electrodes limits redox-MHD pumping to short times because it cannot sustain the current once charge transfer in the film is completed, unlike diffusionlimited redox species in solution. The device used in this study takes advantage of the highly reversible nature of PEDOT to sustain redox-MHD over indefinitely long periods by recycling PEDOT in real time.This study used an array chip with microband and microdisk-ring electrodes (Fig. 1) and a solution confined over them with a gasket and lid. Polystyrene latex beads (10 µm) added to the electrolyte solution allowed visualization of fluid movement using video microscopy. The chip was placed on an electromagnet with a magnetic field (0.033 T RMS) perpendicular to the chip. The electrodes were modified with a conducting polymer, PEDOT, instead of redox species added to solution, to generate an ionic current from the electrochemical reaction at the films, avoiding bubble formation and electrode corrosion.Synchronized sinusoidal potential waveforms applied to PEDOTmodified electrodes (producing an AC curre...

Chip-Scale Electrodeposition and Analysis of Poly(3,4-ethylenedioxythiophene) (PEDOT) Films for Enhanced and Sustained Microfluidics Using DC-Redox-Magnetohydrodynamics

“…20 Also, lower alternating frequencies would be required in AC-MHD, which would diminish inductive heating when synchronizing a sinusoidally varying magnetic field of an electromagnet with a sinusoidally varying current at the PEDOT-modified electrodes to pump fluid indefinitely in a single direction. 33 Electropolymerization of a conducting polymer can provide controlled growth with good adhesion to the substrate and allows transport of dopant ions during monomer oxidation and reduction, affecting film morphology, charge compensation dynamics and charge capacity. 26 PEDOT can be electrodeposited with potentiodynamic (e.g.…”