On-chip microfluidic buffer swap of biological samples in-line with downstream dielectrophoresis.

Microfluidic cell enrichment by dielectrophoresis, based on biophysical and electrophysiology phenotypes, requires that cells be resuspended from their physiological media into a lower conductivity buffer for enhancing force fields and enabling the dielectric contrast needed for separation. To ensure that sensitive cells are not subject to centrifugation for resuspension and spend minimal time outside of their culture media, we present an on-chip microfluidic strategy for swapping cells into media tailored for dielectrophoresis. This strategy transfers cells from physiological media into a 100-fold lower conductivity media by using tangential flows of low media conductivity at 200-fold higher flow rate versus sample flow to promote ion diffusion over the length of a straight channel architecture that maintains laminarity of the flow-focused sample and minimizes cell dispersion across streamlines. Serpentine channels are used downstream from the flow-focusing region to modulate hydrodynamic resistance of the central sample outlet versus flanking outlets that remove excess buffer, so that cell streamlines are collected in the exchanged buffer with minimal dilution in cell numbers and at flow rates that support dielectrophoresis. We envision integration of this on-chip sample preparation platform prior to or post-dielectrophoresis, in-line with on-chip monitoring of the outlet sample for metrics of media conductivity, cell velocity, cell viability, cell position, and collected cell numbers, so that the cell flow rate and streamlines can be tailored for enabling dielectrophoretic separations from heterogeneous samples.

Germanium Quantum-Well Josephson Field-Effect Transistors and Interferometers.

Hybrid superconductor-semiconductor structures attract increasing attention owing to a variety of potential applications in quantum computing devices. They can serve the realization of topological superconducting systems as well as gate-tunable superconducting quantum bits. Here, we combine a SiGe/Ge/SiGe quantum-well heterostructure hosting high-mobility two-dimensional holes and aluminum superconducting leads to realize prototypical hybrid devices, such as Josephson field-effect transistors (JoFETs) and superconducting quantum interference devices (SQUIDs). We observe gate-controlled supercurrent transport with Ge channels as long as one micrometer and estimate the induced superconducting gap from tunnel spectroscopy measurements. Transmission electron microscopy reveals the diffusion of Ge into the Al contacts, whereas no Al is detected in the Ge channel.

Using Electrochemical Immunoassay in a Novel Microtiter Plate to Detect Surface Markers of Preeclampsia on Urinary Extracellular Vesicles.

Extracellular vesicles (EVs) are lipid bilayer nanovesicles secreted by cells. EVs contain biological information related to parental cells and provide biomarkers for disease diagnosis. We have previously shown that the levels of podocin and nephrin expression on urinary EVs may be used to diagnose renal injury associated with preeclampsia. This paper describes a nanoparticle-enabled immunoassay integrated with an electrochemical plate for quantifying podocin and nephrin expression in urinary EVs. The strategy entailed capturing EVs on an electrode surface and then labeling EVs with gold nanoparticles that are both functionalized with antibodies for target specificity and impregnated with redox-active metal ions for electrochemical detection. These immunoprobes produced an electrochemical redox signal proportional to the expression level of EV surface markers. Electrochemical immunoassays were carried out in a novel microtiter plate that contained 16 wells with working electrodes connected to onboard counter/reference electrodes via capillary valves. Upon validation with recombinant proteins, a microtiter plate was used for analysis of urinary EVs from healthy and preeclamptic pregnant women. This analysis revealed a higher podocin to nephrin ratio for preeclamptic women compared to healthy controls (4.31 vs 1.69) suggesting that this ratio may be used for disease diagnosis.

A Compact Control System to Enable Automated Operation of Microfluidic Bioanalytical Assays.

We describe a control system for operating valve-enabled microfluidic devices and leverage this control system to carry out a complex workflow of plasma separation from 8 µL of whole blood followed by on-chip mixing of plasma with assay reagents for biomarker detection. The control system incorporates pumps, digital pressure sensors, a microcontroller, solenoid valves and off-the-shelf components to deliver high and low air pressure in the desired temporal sequence to meter fluid flow and actuate microvalves. Importantly, our control system is portable, which is suitable for operating the microvalve-enabled microfluidic devices in the point-of-care setting.

Self-aligned sequential lateral field non-uniformities over channel depth for high throughput dielectrophoretic cell deflection.

Dielectrophoresis (DEP) enables the separation of cells based on subtle subcellular phenotypic differences by controlling the frequency of the applied field. However, current electrode-based geometries extend over a limited depth of the sample channel, thereby reducing the throughput of the manipulated sample (sub-µL min-1 flow rates and <105 cells per mL). We present a flow through device with self-aligned sequential field non-uniformities extending laterally across the sample channel width (100 µm) that are created by metal patterned over the entire depth (50 µm) of the sample channel sidewall using a single lithography step. This enables single-cell streamlines to undergo progressive DEP deflection with minimal dependence on the cell starting position, its orientation versus the field and intercellular interactions. Phenotype-specific cell separation is validated (>µL min-1 flow and >106 cells per mL) using heterogeneous samples of healthy and glutaraldehyde-fixed red blood cells, with single-cell impedance cytometry showing that the DEP collected fractions are intact and exhibit electrical opacity differences consistent with their capacitance-based DEP crossover frequency. This geometry can address the vision of an "all electric" selective cell isolation and cytometry system for quantifying phenotypic heterogeneity of cellular systems.