Monitoring microfluidic interfacial flows using impedance spectroscopy

Abstract

Microfluidic platforms capable of complex on-chip processing and liquid handling enable a wide variety of sensing, cellular, and material-related applications across a spectrum of disciplines in engineering and biology. However, there is a general lack of available microscale sensors capable of non-optically monitoring and quantifying on-chip fluid motion. Hence, many microfluidic systems are confined to the laboratory because their use requires optical microscopy. Here, we present a method for dynamically tracking laminar interfacial flows in microfluidic channels non-optically using impedance spectroscopy. Using a microfluidic T-channel, we generate a liquid interface by coflowing two different electrolyte streams side-by-side. The interface is driven through an array of "displacement" electrodes where it is electrokinetically deflected across the microchannel. The interfacial flow is monitored downstream using an array of interdigitated "impedance" electrodes which dynamically measure the electrochemical impedance near the surface of the flow channel. We demonstrate that the impedance spectrum is sensitively influenced by the position of the deflected interface. While laminar fluid interfaces are ubiquitous to microfluidic flows and used extensively in rheology and biomolecular detection, it is currently difficult to measure their position non-optically. The sensing method presented here enables the interfacial position to be dynamically determined without a microscope and provides a new tool for lowering the barriers to operating microfluidic devices outside the confines of a traditional laboratory.

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

“…EDL is the charge stored at the interface between electrode and electrolyte due to diffusion dynamics. 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.…”

EIS_Response_Non-planar_Interdigitated_microelectrode_Communication_Paper_JECS

“…This is accomplished in our NP-µIDE device by employing a flow-based detection mode. 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).…”

Correlating Antibiotic-Induced Dysbiosis to Clostridioides difficile Spore Germination and Host Susceptibility to Infection Using an Ex Vivo Assay

“…Recovery from dysbiosis after antibiotic treatment was validated by showing its ability to resist CDI. Microfluidic detection of single bacterial cells ,,− and on-chip culture systems , have emerged in several recent works. Specifically, we show that since impedance cytometry is designed to quantify limited numbers of vegetative bacteria within small sample volumes, it is well suited for high-sensitivity quantification of spore germination.…”