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This study used impedance spectroscopy measurements to extract the electrical properties of phytoplankton cells in suspension. Experimental measurements were acquired, and the single-shell model was applied to extract the specific membrane capacitance, cytoplasm permittivity, and conductivity of assumingly spherical cells in suspension utilizing Maxwell’s mixture theory of a controlled volume fraction of cells. The impedance of suspensions of algae was measured at different frequencies ranging from 3 kHz to 10 MHz and impedance values were compared to investigate differences between two types of cells by characterizing their change in cytoplasm permittivity and specific membrane capacitance. Differentiation between healthy control and nitrogen-depleted cultured algae was attempted. The extracted specific membrane capacitances of Chlamydomonas and Selenastrum were 15.5 ± 3.6 and 40.6 ± 12.6 mF m− 2 respectively. Successful differentiation based on the specific membrane capacitance of different algae species was achieved. However, no significant difference was noticed between nitrogen-abundant and nitrogen-depleted cultures.

Isomotive dielectrophoresis (isoDEP) is a unique electric field such that the gradient of the field-squared ([Formula: see text]) is constant, resulting a uniform dielectrophoretic force. The current status of isoDEP is presented in this review, and we will highlight the progress that has been achieved over the past 60 years in various avenues of isoDEP since H.A. Pohl initially described its premise. This article will discuss its applications and describe the various configurations of generating an isomotive force. Since H.A. Pohl introduced the theory of isoDEP, numerous authors have implemented isoDEP as a tool for the manipulation, sorting, separation, and characterization of polarizable particles without the need for biochemical labels or other bioengineered tagging. The growing field of microfluidics and electrokinetics has renewed interest in isoDEP, particularly for analytical characterization or separation of particles. Recent work has demonstrated that isoDEP can address some unmet needs for biomedical applications including single-cell analysis; moreover, advances in throughput as well as combining characterization and separation simultaneously will add significant value to isoDEP.

When a sessile droplet of a complex mixture evaporates, its nonvolatile components may deposit into various patterns. One such phenomena, the coffee ring effect, has been a topic of interest for several decades. Here, we identify what we believe to be a fascinating phenomenon of droplet pattern deposition for another well-known beverage-what we have termed a "whiskey web". Nanoscale agglomerates were generated in diluted American whiskeys (20-25% alcohol by volume), which later stratified as microwebs on the liquid-air interface during evaporation. The web's strandlike features result from monolayer collapse, and the resulting pattern is a function of the intrinsic molecular constituents of the whiskey. Data suggest that, for our conditions (diluted 1.0 μL drops evaporated on cleaned glass substrates), whiskey webs were unique to diluted American whiskey; however, similar structures were generated with other whiskeys under different conditions. Further, each product forms their own distinct pattern, demonstrating that this phenomenon could be used for sample analysis and counterfeit identification.

The dynamic manipulation and assembly of colloids enables the advancement of analytical techniques in biotechnology and the development of self-assembled materials. Rapid electrokinetic patterning (REP) is a hybrid optoelectrokinetic technique that simultaneously uses a laser illumination and a uniform AC electric field to yield programmable, dynamic, and non-invasive manipulation of colloidal particles. Since it was introduced, the technique has been applied to microengineering and biological research fields, showing its promising capabilities as a great tool for trapping, aggregating, translating, and sorting single and multiple micro- and nanoparticles, including bacteria. To effectively leverage and enhance these applications, this review paper will highlight its versatility and capability, including REP’s principles, governing physics, different experimental setups, fabrications, applications, and future prospects.

Isomotive dielectrophoresis (isoDEP) is a unique DEP geometrical configuration where the gradient of the field-squared ( ∇ E rms 2 ) is constant. IsoDEP analyzes polarizable particles based on their magnitude and direction of translation. Particle translation is a function of the polarizability of both the particles and suspending medium, the particles' size and shape, and the frequency of the electric field. However, other electrokinetics act on the particles simultaneously, including electrothermal hydrodynamics. Hence, to maximize the DEP force relative to over electrokinetic forces, design parameters such as microchannel geometry, fabrication materials, and applied electric field must be properly tuned. In this work, scaling law analyses were developed to derive design rules, relative to particle diameter, to reduce unwanted electrothermal hydrodynamics relative to DEP-induced particle translation. For a particle suspended in 10 mS/m media, if the channel width and height are below ten particle diameters, the electrothermal-driven flow is reduced by ∼500 times compared to a channel that is 250 particles diameters in width and height. Replacing glass with silicon as the device's underlying substrate for an insulative-based isoDEP reduces the electrothermal induced flow approximately 20 times less.

Coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was classified as a pandemic by the World Health Organization and has caused over 550,000 deaths worldwide as of July 2020. Accurate and scalable point-of-care devices would increase screening, diagnosis, and monitoring of COVID-19 patients. Here, we demonstrate rapid label-free electrochemical detection of SARS-CoV-2 antibodies using a commercially available impedance sensing platform. A 16-well plate containing sensing electrodes was pre-coated with receptor binding domain (RBD) of SARS-CoV-2 spike protein, and subsequently tested with samples of anti-SARS-CoV-2 monoclonal antibody CR3022 (0.1 μg/ml, 1.0 μg/ml, 10 μg/ml). Subsequent blinded testing was performed on six serum specimens taken from COVID-19 and non-COVID-19 patients (1:100 dilution factor). The platform was able to differentiate spikes in impedance measurements from a negative control (1% milk solution) for all CR3022 samples. Further, successful differentiation and detection of all positive clinical samples from negative control was achieved. Measured impedance values were consistent when compared to standard ELISA test results showing a strong correlation between them (R2=0.9). Detection occurs in less than five minutes and the well-based platform provides a simplified and familiar testing interface that can be readily adaptable for use in clinical settings., Highlights • Capacitive immunosensing of clinically relevant concentrations of SARS-CoV-2 antibodies. • Antigen/antibody association and dissociation occurs within few seconds. • Rapid, label free detection using commercially available equipment. • Impedance peaks correlated with CR3022 concentration levels and ELISA measurements.

This paper reports a method for label‐free single‐cell biophysical analysis of multiple cells trapped in suspension by electrokinetic forces. Tri‐dimensional pillar electrodes arranged along the width of a microfluidic chamber define actuators for single cell trapping and selective release by electrokinetic force. Moreover, a rotation can be induced on the cell in combination with a negative DEP force to retain the cell against the flow. The measurement of the rotation speed of the cell as a function of the electric field frequency define an electrorotation spectrum that allows to study the dielectric properties of the cell. The system presented here shows for the first time the simultaneous electrorotation analysis of multiple single cells in separate micro cages that can be selectively addressed to trap and/or release the cells. Chips with 39 micro‐actuators of different interelectrode distance were fabricated to study cells with different sizes. The extracted dielectric properties of Henrietta Lacks, human embryonic kidney 293, and human immortalized T lymphocytes cells were found in agreements with previous findings. Moreover, the membrane capacitance of M17 neuroblastoma cells was investigated and found to fall in in the range of 7.49 ± 0.39 mF/m2.

Late embryogenesis abundant (LEA) proteins are found in desiccation-tolerant species from all domains of life. Despite several decades of investigation, the molecular mechanisms by which LEA proteins confer desiccation tolerance are still unclear. In this study, dielectrophoresis (DEP) was used to determine the electrical properties of Drosophila melanogaster (Kc167) cells ectopically expressing LEA proteins from the anhydrobiotic brine shrimp, Artemia franciscana. Dielectrophoresis-based characterization data demonstrate that the expression of two different LEA proteins, AfrLEA3m and AfrLEA6, increases cytoplasmic conductivity of Kc167 cells to a similar extent above control values. The impact on cytoplasmic conductivity was surprising, given that the concentration of cytoplasmic ions is much higher than the concentrations of ectopically expressed proteins. The DEP data also supported previously reported data suggesting that AfrLEA3m can interact directly with membranes during water stress. This hypothesis was strengthened using scanning electron microscopy, where cells expressing AfrLEA3m were found to retain more circular morphology during desiccation, while control cells exhibited a larger variety of shapes in the desiccated state. These data demonstrate that DEP can be a powerful tool to investigate the role of LEA proteins in desiccation tolerance and may allow to characterize protein-membrane interactions in vivo, when direct observations are challenging.