Hydrodynamic and electrical considerations in the design of a four-electrode impedance-based microfluidic device

Abstract

A four-electrode impedance-based microfluidic device has been designed with tunable sensitivity for future applications to the detection of pathogens and functionalized microparticles specifically bound to molecular recognition molecules on the surface of a microfluidic channel. In order to achieve tunable sensitivity, hydrodynamic focusing was employed to confine the electric current by simultaneous introduction of two fluids (high- and low-conductivity solutions) into a microchannel at variable flow-rate ratios. By increasing the volumetric flow rate of the low-conductivity solution (sheath fluid) relative to the high-conductivity solution (sample fluid), increased focusing of the high-conductivity solution over four coplanar electrodes was achieved, thereby confining the current during impedance interrogation. The hydrodynamic and electrical properties of the device were analyzed for optimization and to resolve issues that would impact sensitivity and reproducibility in subsequent biosensor applications. These include variability in the relative flow rates of the sheath and sample fluids, changes in microchannel dimensions, and ionic concentration of the sample fluid. A comparative analysis of impedance measurements using four-electrode versus two-electrode configurations for impedance measurements also highlighted the advantages of using four electrodes for portable sensor applications.

Communication—Electrochemical Impedance Signature of a Non-Planar, Interdigitated, Flow-Through, Porous, Carbon-Based Microelectrode

“…44 The Nyquist plots (Figure 3) indicate that the EDL capacitor discharges at a significantly higher frequency (∼300 kHz) in comparison to other EIS spectra found in the literature (1Hz to 1kHZ) which shifts the Rct to significantly higher frequency. [45][46][47] This shift is due to the disruption in the diffuse layer dynamics through the introduction of enhanced convective transport from the packed r-GO. It is worthwhile to note that the EIS data from 1 kHz to 100 MHz takes a mere 30 seconds to obtain even after 8 points averaging method used by us for noise reduction.…”

Biosensor technology: recent advances in threat agent detection and medicine

“…165 in impedance-based biosensors by creating an adjustable, softwalled ''virtual'' microchannel. 166,167 McGraw et al proposed using electrotextiles such as a polypropylene microfiber membrane coated with polypyrrole and antibodies for highly sensitive detection of pathogens, allowing for the creation of light-weight and flexible sensors. 126,168 Wojciechowski et al proposed using organic photodiodes to provide cheap and miniaturized optical transduction, allowing for the possibility of portable and disposable optical biosensors.…”

EIS_Response_Non-planar_Interdigitated_microelectrode_Communication_Paper_JECS

“…EDL is the charge stored at the interface between electrode and electrolyte due to diffusion dynamics (39). The Nyquist plots (figure 3) indicate that the EDL capacitor discharges at a significantly higher frequency (~300 kHz) in comparison to other EIS spectra found in literature (1Hz to 1kHZ) which shifts the Rct to significantly higher frequency (40)(41)(42). This shift is due to the disruption in the diffuse layer dynamics through the introduction of enhanced convective transport from the packed r-GO.…”