Poly(3,4-ethylenedioxythiophene)-Modified Electrodes for Microfluidics Pumping with Redox-Magnetohydrodynamics: Improving Compatibility for Broader Applications by Eliminating Addition of Redox Species to Solution

Abstract

A new approach using electrodes modified with poly(3,4-ethylenedioxythiophene) (PEDOT) was implemented to perform redox-magnetohydrodynamics (MHD) microfluidics and eliminate the need to add redox species to solution, thus removing interferences with detection, sample, and reagents for lab-on-a-chip applications. This accomplishment not only retains the unique properties of redox-MHD pumping (i.e., programmable fluid speeds and flow patterns without the need for side walls, horizontal flat flow profiles, looping flow, no electrode corrosion, and no bubble formation), but also achieves a wider sustainable voltage range and currents that can be as much as 7+ times higher (and therefore correspondingly higher velocities) than in past studies involving unmodified electrodes and redox species in solution. PEDOT, a conducting polymer that has been shown to exhibit low cytotoxicity, was electropolymerized on microband gold electrodes (25 mm long ×103 μm wide). A cell (325 μL) with distant side walls was formed by placing a 620 μm thick poly(dimethylsiloxane), PDMS, gasket with an opening of 3.2 cm × 1.5 cm on the chip, and a glass slide lid prevented evaporation. A 0.37 T magnet under the chip generated a magnetic field perpendicular to the chip surface. The cell was filled with 0.095 M NaCl electrolyte containing 10 μm polystyrene beads to visualize and quantify fluid flow using optical video microscopy. Fluid speeds of 590 μm s(-1) were observed immediately after applying a potential step. A linear relationship between applied electronic current and fluid velocity was shown. Vertical flow profiles under applied current conditions were curved, with a weak parabolic fit.

Elucidating the Structure–Function Relationship of Poly(3,4-theylenedioxythiophene) Films to Advance Electrochemical Measurements

“…Of specific interest here are applications of PEDOT as a working electrode material for biosensor applications such as the electrochemical detection of biological analytes, including neurotransmitters. ,− Neurotransmitters such as dopamine, norepinephrine, and serotonin are of interest because they have important physiological roles in regulating behavior, cognition, and other brain functions and are redox active. − In most applications aimed at neurotransmitter detection, PEDOT is used as a coating to improve the electrochemical performance of another electrode material, often platinum. − However, there has been some investigation into using PEDOT-only electrodes as the working electrode material for these measurements. , Unfortunately, most of these studies are application driven and there is little understood about the critical parameters that control the electrochemical properties and therefore how to improve said properties.…”

Redox-Magnetohydrodynamically Controlled Fluid Flow with Poly(3,4-ethylenedioxythiophene) Coupled to an Epitaxial Light Sheet Confocal Microscope for Image Cytometry Applications

“…Integrating the current over 20 s gives a total charge of 88.6 ± 1.4 mC/cm 2 , which corresponds to a capacitive density of 55.4 ± 0.9 mF/cm 2 (for a 1.6 V excursion). These are about 1.5 and 4 times the area-normalized electronic current and capacitance values, respectively, than films reported by us previously . Therefore, the maximum fluid speed and distance pumped should be improved proportionally for similar chamber dimensions.…”

“…In addition, they require either external actuators or an additional pump (to create pressure/vacuum) and check valves that involve complex fabrication. Recent advances in microfluidics pumped by redox-magnetohydrodynamics (R-MHD) have not only demonstrated a requisite flat horizontal flow profile , but also expanded compatibility with biological samples by using immobilized redox films at the electrode and improved linear fluid velocity . On-chip R-MHD pumping is also relatively simpler to fabricate and more easily programs fluid flow than membrane-based pumps.…”

“…MHD generates a body force, F B (N/m 3 ), when an external magnetic field B (T) is perpendicular to ionic current density j (C/s m 2 ), which can be generated between a pair of electrodes in a fluid, and follows the right-hand rule F B = j × B . − Adding redox species to an electrolyte solution facilitates conversion of electronic to ionic current without bubble generation and electrode corrosion. , This generates sufficient ionic current with low voltage for microfluidic propulsion in the presence of low | B | from a permanent magnet but suffers from interference issues. , We have immobilized the conducting polymer poly­(3,4-ethylenedioxythiophene) (PEDOT) onto electrode surfaces to replace solution redox species and therefore avoid chemical interferences, achieve higher currents (and velocities), and afford easier use . However, its finite charge capacity can limit operation time, and its electrodeposition from aqueous solutions onto the R-MHD electrodes is time-consuming and requires a solubilizer.…”

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

“…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 ]. One of the advantages of adding redox species to MHD-based systems is the possibility of avoiding bubble generation on electrodes and their consequent degradation, as the redox species serves as a sacrificial element.…”