We
investigated the dependence of ion transport through perforated
graphene on the concentrations of the working ionic solutions. We
performed our measurements using three salt solutions, namely, KCl,
LiCl, and K2SO4. At low concentrations, we observed
a high membrane potential for each solution while for higher concentrations
we found three different potentials corresponding to the respective
diffusion potentials. We demonstrate that our graphene membrane, which
has only a single layer of atoms, showed a very similar trend in membrane
potential as compared to dense ion-exchange membranes with finite
width. The behavior is well explained by Teorell, Meyer, and Sievers
(TMS) theory, which is based on the Nernst–Planck equation
and electroneutrality in the membrane. The slight overprediction of
the theoretical Donnan potential can arise due to possible nonidealities
and surface charge regulation effects.
Microfluidic impedance flow cytometers enable high-throughput, non-invasive, and label-free detection of single-cells. Cytometers with coplanar electrodes are easy and cheap to fabricate, but are sensitive to positional differences of passing particles, owing to the inhomogeneous electric field. We present a novel particle height compensation method, which employs the dependence of measured electrical opacity on particle height. The measured electrical opacity correlates with the particle height as a result of the constant electrical double layer series capacitance of the electrodes. As an alternative to existing compensation methods, we use only two coplanar electrodes and multi-frequency analysis to determine the particle size of a mixture of 5, 6, and 7 µm polystyrene beads with an accuracy (CV) of 5.8%, 4.0%, and 2.9%, respectively. Additionally, we can predict the bead height with an accuracy of 1.5 µm (8% of channel height) using the measured opacity and we demonstrate its application in flow cytometry with yeast. The use of only two electrodes is of special interest for simplified, easy-to-use chips with a minimum amount of instrumentation and of limited size.
We demonstrate a new method to induce vortices with AC-EOF by shaping insulator materials near parallel electrodes, giving control of vortex organization. Interestingly, non-orthogonality of insulator walls is a requirement to induce AC-EOF.
We report the fabrication of a microreactor with embedded internal reflection element (IRE) and herringbone (HB) micromixer. The microreactor can be used as a powerful tool for monitoring in-situ chemical reactions when combined with attenuated total internal reflection (ATR) infrared (IR) spectroscopy. In this work, a H2O/D2O model reaction was monitored as a proof of concept and the HOD product formation was spatially tracked. In addition to this, a mixing efficiency of 99% at 25 cycles was also calculated for the microreactor.
Microfluidic electrical flow cytometry is a popular method to study a wide variety of biological cell properties. Unfortunately, when using coplanar electrodes, this method is sensitive to positional differences of passing particles or cells.In this work we present a novel compensation method to account for the particle position in a coplanar electrode setup using the measured electrical opacity.We demonstrate an accurate size discrimination of 5, 6 and 7 µm polystyrene beads irrespective of their position using the measured electrical opacity making use of the variation of electrical field strength with height in the channel. Thus, only two electrodes are required, which is favorable for microfluidic devices with size limitations.
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