Microdevices for separation, accumulation, and analysis of biological micro- and nanoparticles

Manipulation, Sampling and Inactivation of the SARS-CoV-2 Virus Using Nonuniform Electric Fields on Micro-Fabricated Platforms: A Review

Micro-devices that use electric fields to trap, analyze and inactivate micro-organisms vary in concept, design and application. The application of electric fields to manipulate and inactivate bacteria and single-celled organisms has been described extensively in the literature. By contrast, the effect of such fields on viruses is not well understood. This review explores the possibility of using existing methods for manipulating and inactivating larger viruses and bacteria, for smaller viruses, such as SARS-CoV-2. It also provides an overview of the theoretical background. The findings may be used to implement new ideas and frame experimental parameters that optimize the manipulation, sampling and inactivation of SARS-CoV-2 electrically.

Microfluidic Isolation and Enrichment of Nanoparticles

Over the past decades, nanoparticles have increased in implementation to a variety of applications ranging from high-efficiency electronics to targeted drug delivery. Recently, microfluidic techniques have become an important tool to isolate and enrich populations of nanoparticles with uniform properties (e.g., size, shape, charge) due to their precision, versatility, and scalability. However, due to the large number of microfluidic techniques available, it can be challenging to identify the most suitable approach for isolating or enriching a nanoparticle of interest. In this review article, we survey microfluidic methods for nanoparticle isolation and enrichment based on their underlying mechanisms, including acoustofluidics, dielectrophoresis, filtration, deterministic lateral displacement, inertial microfluidics, optofluidics, electrophoresis, and affinity-based methods. We discuss the principles, applications, advantages, and limitations of each method. We also provide comparisons with bulk methods, perspectives for future developments and commercialization, and next-generation applications in chemistry, biology, and medicine.

Numerical modelling and measurement of cell trajectories in 3-D under the influence of dielectrophoretic and hydrodynamic forces

This research is part of a program aiming at the development of a fluidic microsystem for in vitro drug testing. For this purpose, primary cells need to be assembled to form cellular aggregates in such a way as to resemble the basic functional units of organs. By providing for in vivo-like cellular contacts, proper extracellular matrix interaction and medium perfusion it is expected that cells will retain their phenotype over prolonged periods of time. In this way, in vitro test systems exhibiting in vivo type predictivity in drug testing are envisioned. Towards this goal a 3-D microstructure micro-milled in a cyclic olefin copolymer (COC) was designed in such a way as to assemble liver cells via insulator-based dielectrophoresis (iDEP) in a sinusoid-type fashion. First, numeric modelling and simulation of dielectrophoretic and hydrodynamic forces acting on cells in this microsystem was performed. In particular, the problem of the discontinuity of the electric field at the interface between the fluid media in the system and the polymer materials it consists of was addressed. It was shown that in certain cases, the material of the microsystem may be neglected altogether without introducing considerable error into the numerical solution. This simplification enabled the simulation of 3-D cell trajectories in complex chip geometries. Secondly, the assembly of HepG2 cells by insulator-based dielectrophoresis in this device is demonstrated. Finally, theoretical results were validated by recording 3-D cell trajectories and the Clausius-Mossotti factor of liver cells was determined by combining results obtained from both simulation and experiment.

LAB-ON-CHIP-BASED CELL SEPARATION BY COMBINING DIELECTROPHORESIS AND CENTRIFUGATION

Cell-based approaches in medicine, biotechnology and in pharmaceutical research offer unique prospects to cope with future challenges in the field of public health. Stem cell research, autologous cell therapies and tissue engineering are only a few possible key applications. Progress in these fields will depend on the successful implementation of versatile and flexible tools for the gentle manipulation and characterization of cells. In recent years, we and others have introduced microfluidic lab-on-chip systems that include dielectrophoretic elements for the contact-less handling and the analysis of cells. Here, we present results that were obtained by combining our labon-on-chip devices with a low-cost centrifugation stage for the efficient and gentle separation of microparticles and live human cells. Our approach is supposed to overcome limitations that arise from the use of bulky and expensive external pumping stages.

Review article-dielectrophoresis: status of the theory, technology, and applications

A review is presented of the present status of the theory, the developed technology and the current applications of dielectrophoresis (DEP). Over the past 10 years around 2000 publications have addressed these three aspects, and current trends suggest that the theory and technology have matured sufficiently for most effort to now be directed towards applying DEP to unmet needs in such areas as biosensors, cell therapeutics, drug discovery, medical diagnostics, microfluidics, nanoassembly, and particle filtration. The dipole approximation to describe the DEP force acting on a particle subjected to a nonuniform electric field has evolved to include multipole contributions, the perturbing effects arising from interactions with other cells and boundary surfaces, and the influence of electrical double-layer polarizations that must be considered for nanoparticles. Theoretical modelling of the electric field gradients generated by different electrode designs has also reached an advanced state. Advances in the technology include the development of sophisticated electrode designs, along with the introduction of new materials (e.g., silicone polymers, dry film resist) and methods for fabricating the electrodes and microfluidics of DEP devices (photo and electron beam lithography, laser ablation, thin film techniques, CMOS technology). Around three-quarters of the 300 or so scientific publications now being published each year on DEP are directed towards practical applications, and this is matched with an increasing number of patent applications. A summary of the US patents granted since January 2005 is given, along with an outline of the small number of perceived industrial applications (e.g., mineral separation, micropolishing, manipulation and dispensing of fluid droplets, manipulation and assembly of micro components). The technology has also advanced sufficiently for DEP to be used as a tool to manipulate nanoparticles (e.g., carbon nanotubes, nano wires, gold and metal oxide nanoparticles) for the fabrication of devices and sensors. Most efforts are now being directed towards biomedical applications, such as the spatial manipulation and selective separationenrichment of target cells or bacteria, high-throughput molecular screening, biosensors, immunoassays, and the artificial engineering of three-dimensional cell constructs. DEP is able to manipulate and sort cells without the need for biochemical labels or other bioengineered tags, and without contact to any surfaces. This opens up potentially important applications of DEP as a tool to address an unmet need in stem cell research and therapy.

Dielectrophoretic field-flow method for separating particle populations in a chip with asymmetric electrodes

This paper presents a field-flow method for separating particle populations in a dielectrophoretic (DEP) chip with asymmetric electrodes under continuous flow. The structure of the DEP device (with one thick electrode that defines the walls of the microfluidic channel and one thin electrode), as well as the fabrication and characterization of the device, was previously described. A characteristic of this structure is that it generates an increased gradient of electric field in the vertical plane that can levitate the particles experiencing negative DEP. The separation method consists of trapping one population to the bottom of the microfluidic channel using positive DEP, while the other population that exhibits negative DEP is levitated and flowed out. Viable and nonviable yeast cells were used for testing of the separation method.

The zeta potential of surface-functionalized metallic nanorod particles in aqueous solution

Metallic nanoparticles suspended in aqueous solutions and functionalized with chemical and biological surface coatings are important elements in basic and applied nanoscience research. Many applications require an understanding of the electrokinetic or colloidal properties of such particles. We describe the results of experiments to measure the zeta potential of metallic nanorod particles in aqueous saline solutions, including the effects of pH, ionic strength, metallic composition, and surface functionalization state. Particle substrates tested include gold, silver, and palladium monometallic particles as well as gold/silver bimetallic particles. Surface functionalization conditions included 11-mercaptoundecanoic acid (MUA), mercaptoethanol (ME), and mercaptoethanesulfonic acid (MESA) self-assembled monolayers (SAMs), as well as MUA layers subsequently derivatized with proteins. For comparison, we present zeta potential data for typical charge-stabilized polystyrene particles. We compare experimental zeta potential data with theoretically predicted values for SAM-coated and bimetallic particles. The results of these studies are useful in predicting and controlling the aggregation, adhesion, and transport of functionalized metallic nanoparticles within microfluidic devices and other systems.

Synergism between particle-based multiplexing and microfluidics technologies may bring diagnostics closer to the patient

In the field of medical diagnostics there is a growing need for inexpensive, accurate, and quick high-throughput assays. On the one hand, recent progress in microfluidics technologies is expected to strongly support the development of miniaturized analytical devices, which will speed up (bio)analytical assays. On the other hand, a higher throughput can be obtained by the simultaneous screening of one sample for multiple targets (multiplexing) by means of encoded particle-based assays. Multiplexing at the macro level is now common in research labs and is expected to become part of clinical diagnostics. This review aims to debate on the “added value” we can expect from (bio)analysis with particles in microfluidic devices. Technologies to (a) decode, (b) analyze, and (c) manipulate the particles are described. Special emphasis is placed on the challenges of integrating currently existing detection platforms for encoded microparticles into microdevices and on promising microtechnologies that could be used to down-scale the detection units in order to obtain compact miniaturized particle-based multiplexing platforms.

Accumulation and trapping of hepatitis A virus particles by electrohydrodynamic flow and dielectrophoresis

Hepatitis A virus particles (d = 27 nm) were successfully accumulated and trapped in a microfluidic system by means of a combination of electrohydrodynamic flow and dielectrophoretic forces. Electric fields were generated in a field cage consisting of eight microelectrodes. In addition, high medium conductance (0.3 S/m) resulted in sufficient Joule heating and the corresponding spatial variation of temperature, density, and permittivity to induce electrohydrodynamic flow in the vicinity of the field cage. Flow vortices transport particles toward the center of the field cage, where dielectrophoretic forces cause permanent entrapment and particle aggregation. Spatial distribution of temperature, density, and permittivity as well as resulting flow patterns were modeled numerically and are in good agreement with experimental results. This accumulation scheme might be applicable to sample concentration enhancement in biosensor applications.

An efficient cell separation system using 3D-asymmetric microelectrodes

An efficient 3D-asymmetric microelectrode system for high-throughput was designed and fabricated to enhance sorting sensitivities to the dielectric properties-size, morphology, conductivity, and permittivity-of living cells. The principle of the present system is based on the use of the relative strengths of negative dielectrophoretic and drag forces, as in a conventional 3D-microelectrode system. Whereas the typical 3D-microelectrode system has a constant electric field magnitude due to the constant width of the microelectrodes and a fixed gap between face-to-face microelectrodes, the present 3D-asymmetric microelectrode system has electric fields of continuously varying magnitudes along the transverse direction of a channel owing to the changing widths of the electrodes in the half-circular shaped cross section of the microchannel. Thus, varying dielectric forces are generated, leading to increased sorting sensitivity through differentially induced forces to definitely distinct cell types. Numerical analysis verified the improved sensitivity of the present system for sorting living cells. The feasibility of using the newly fabricated system under experimental conditions was tested by demonstrating that a mixed population of mouse P19 embryonic carcinoma (EC) and red blood cells (RBCs) was effectively sorted to different wells depending on their respective relative physical properties.