Tunable membrane-less dielectrophoretic microseparation by crossing interdigitated electrodes

We present numerical simulations and experiments on dielectrophoretic (DEP) separation and trapping performed in a titanium-based microchannel linear electrode array. The use of electric fields and in particular dielectrophoresis (DEP) have a great potential to help miniaturize and increase the speed of biomedical analysis. Precise control and manipulation of micro/nano/bio particles inside those miniaturized devices depend greatly on our understanding of the phenomena induced by AC electric fields inside microchannels and how we take advantage of them. The studied DEP devices are composed of two parts: the inter-digitated titanium electrodes and the channel. The electrode substrate is constituted of two layers to form 4-phase traveling wave. Each electrode is 20 μm wide and separated from the other by a gap of 20 μm. The channel is 200 μm wide, 50 μm deep and 6 mm long. The device is designed to generate inhomogeneities in electric-field magnitude. This allows positive and negative DEP (p-DEP and n-DEP). Moreover, it can also produce inhomogeneities in electric-field phase, hence authorizing traveling wave DEP (twDEP). It is also capable of inducing two-frequency DEP, in contrast with most of the previous, single-frequency, designs. The advantages of two-frequency DEP were shown by theoretical work (Chang et al. 2003) and permit precise and optimal control of particles movements. We show that fluid flow effects are substantial and can affect the particle motion in a positive (enhanced trapping) and negative (trapping when separation is desired) way. We discuss the effects of AC-electroosmosis, electrothermal and dielectrophoresis combined. We discuss the advantages of two-frequency dielectrophoretic handling of bioparticles. We investigate the limits of particle size that can be accurately controlled.

Dielectrophoretic (DEP) cell sorting platforms working in continuous mode are advantageous over those in batch mode due to their expanded sample capacity, fast processing as well as simple operation. State-of-art DEP activated cell separators leverage continuous-flow cell sorting with slanted digits made of metal film patterned on channel bottom or 3D bulk electrode embedded in channel sidewall, which project DEP force field that laterally deflect the cells as they proceed in the channel. However, these designs have limited channel depth or width which hamper their volumetric flow rate. Recently we report a design of interdigitated silicon electrode digits that serve as tracks for cell railing during the separation and achieve cell separation at 8.3 μl/min with 86% separation efficiency for the separated cells. Yet the fabrication process for tailoring the silicon electrode digits involves expensive silicon dry etching process and requires specially designed pattern of the digit featuring non-straight wavy outline, which leads to non-uniform drag force acting on cells. Here we innovatively enable bidirectional cell sliding on V-shaped 3D interdigitated electrode digits that serve as perfectly straight sliding tracks. Such ideal sliding tracks significantly enhance the throughput compared to the existing silicon tracks. The electrodes made of silver-PDMS (AgPDMS) composites are fabricated using low-cost soft-lithography process. Bidirectional cell sliding is demonstrated using Hela cells, and high throughput separation of Hela cells from beads is showcased with 85% cell separation efficiency at 20 μl/min sample infusion flow rate.

The paper presents theoretical analysis of flow dynamics in a heated microchannel in which flow rate may be controlled by dielectrophoretic (DEP) forces. Proposed model equations were derived in terms of lumped parameters characterising the system comprising of DEP controller and the microchannel. In result, an equation for liquid height of rise in the controller was obtained from momentum balances in the two elements of the considered system. In the model, the boiling process in the heated section of microchannel is taken into account through a pressure drop, which is a function of flow rate and uniform heat flux. Presented calculation results show that the DEP forces influence mainly the flow rate in the microchannel. In this way, by proper modulation of voltage applied to the DEP controller, it is possible to lower the frequency of Ledinegg instabilities.

The influence of size differences, shape, mass, and persistent motion on phase separation in binary mixtures has been intensively studied. Here we focus on the exclusive role of diffusivity differences in binary mixtures of equal-sized particles. We find an effective attraction between the less diffusive particles, which are essentially caged in the surrounding species with the higher diffusion constant. This effect leads to phase separation for systems above a critical size: A single close-packed cluster made up of the less diffusive species emerges. Experiments for testing our predictions are outlined.

Proposed is a new type optical switch, which consists of an optical divider and a parallel optical shutter. First, optical divider is made of grating designed well, which divides an input beam into three beams. The three beams enter a parallel optical shutter, which consists of PLZT 9/65/35 ceramic plate and three pairs of interdigital electrodes on the plate. Applying about 200 volts to one of three pairs of electrodes, the optical switch turns on and therefore the corresponding beam can pass through the shutter, resulting in working as an optical switch.

Oriented and vectorial immobilization of linear M13 dsDNA between interdigitated electrodes—towards single molecule DNA nanostructures

Critical fluidization velocities and maximum bed pressure drops of homogeneous binary mixture of irregular particles in gas–solid tapered fluidized beds

Marketable value of algal biomass has been increasing in recent years due to its wide range of applications. This study investigates the performance of a novel cylindrical interdigitated electrode array in electrocoagulation for the harvesting of marine microalgae (Tetraselmis sp.). The new electrode array is expected to exert a dielectrophoretic (DEP) force which would assist in the harvesting of the microalgae in the electrocoagulation process. Through numerical investigation, the induction of dielectrophoretic force was confirmed in the new electrode array. In this study, 10 min electrolysis time was found to be sufficient to harvest 82.4% microalgae with 1 cm electrode distance and 50 mA/cm2 current density. Furthermore, decreasing the electrode distance to 0.5 cm increased the algal harvesting efficiency to 96.18%. Energy analysis showed that the proposed electrode array shows 38% lower specific energy consumption than the conventional flat sheet electrode array.

Phase separation in asymmetric binary mixture of large hexagonal and small rhombus particles described within the generalised Frenkel–Louis model

A new type of light modulator, in which incident light polarization is converted to perpendicular polarization by electro-optic effect of r51, was studied, using an a-cut LiTaO3 with a Li/Ta≃1.2 composition. A spatially periodic electric field for phase-matching between two crossed polarizations is generated by a pair of interdigital electrodes. The electrode period is changed along the light path so that phase-match condition can be satisfied over a wide temperature range. Birefringence inhomogeneity along the light path was found to contribute to wider operation temperature ranges. An extinction ratio of above 30 dB and 73% conversion with an applied voltage of 180 V were obtained in the modulator. Measured temperature characteristics were almost coincident with calculated values.

The strong and specific noncovalent interaction between avidin and biotin is widely exploited in different types of enzyme-linked immunosorbent assay kits, labeled immunosensors, and polymer-based sensing devices for the detection of different biomarkers specific to different diseases such as cancer and influenza. Here, we employed the avidin–biotin technology in a novel gold nanoparticle-decorated graphene field-effect transistor (AuNP-GFET) and demonstrated the specific detection of the biotinylated macromolecules such as biotinylated proteins and nucleotides in the sub-picomolar (pM) range. The AuNP-GFET was constructed by fabricating six pairs of interdigital electrodes on graphene transferred on a SiO2/Si substrate. The sensing performance of AuNP-GFET was characterized by the real-time two-terminal electrical current measurement upon injection of the analyte solution into a silicone pool preattached onto the electrodes. Avidin, a tetrameric biotin-binding protein with strong affinity and specificity, immobilized on AuNP-decorated single-layer graphene, was used as the sensing platform and transduced the electrical signal upon binding to the analyte macromolecules. The sensing capability of the AuNP-GFET was tested with the biotinylated protein A. Sensitivity of the present biosensor was estimated to be ∼0.4 pM. The specificity and applicability of the biosensor were confirmed using both synthetic and real samples. Because the biotin label can retain its binding capability to avidin with strong affinity and specificity even after conjugating with varieties of proteins and nucleotides, the present AuNP-GFET biosensor is expected to promote the research in developing different biosensors.

Dielectric measurement and image analysis are used to evaluate the hydrophobic condition of silicone rubber surface. Hydrophobicity of silicone rubber surface was studied by using image data analysis of sprayed water droplets on the sample surface. Hydrophobicity class, HC from 1 to 7, is evaluated by the analyzed image data indices. The water droplets on the sample surface are digitized and the image indices such as size and shape factor of the droplets were evaluated. After this evaluation, 3D mapping technique is used to evaluate the HC value. The hydrophobic condition of the sample surface was also determined by measuring dielectric property of silicone rubber using a pair of inter-digital electrodes. The dielectric properties were detected by using unbalanced operation of current comparator type capacitance bridge. The changes in dielectric loss current and the capacitive current by the change in hydrophobic condition were measured for every one cycle of AC applied field. Comparing of these results can define the degradation of hydrophobicity of polymer insulator more accurately.

The development of textile-based wearable devices has been a hot research topic in recent years. However, a fabric-supported optical switch has never been reported. Herein, a pair of interdigital silver electrodes and hydrothermally synthesized Bi2S3 nanowires (NWs) were screen-printed successively onto silk fabric to construct a silk fabric-based flexible optical switch. The device showed irradiation power-dependent light-on currents and was able to respond to blue, green and red light. A fast response/recovery time of less than 2 ms could be achieved. After 120 cycles of distortion or bending, the light-on current remained as high as >85%. Bi2S3 NW films with different patterns could be printed on top of the devices without significantly affecting their performance. It was also demonstrated that the system could be utilized to trigger the rotation of an electrical fan. This work may provide a facile approach for the preparation of a silk fabric-based optical switch for wearable electronics.

Phthalocyanines and their analogs have practical interest at development devices with low consumption because these materials are known to considerably modify their electrophysical properties on adsorption of the active gases at low temperatures. The conductivity, resistance-temperature relationship, sensor properties relative to NO, O2 and H2S of films based on oligo-(OPc) and polyphthalocyanines (PPc) containing Co, Cu, Fe and Mn were investigated in the present work. Polymeric films were deposited on the test structures with a pair of interdigital metal electrodes. The sensor’s active area was 4.0 × 4.0 mm, and electrode gap was egual 0.08 mm. The sensitive layers were formed by two methods. The soluble OPcs were deposited from their saturated dimethylformamide solutions and insoluble PPcs were deposited by the thermal sputtering in vacuum. The investigations were carried out under the sensor thermal stabilization conditions in the range 50–250 °C with the constant values of the heater resistance.

Pt and WO3 co-loaded ZrO2 equipped with a pair of interdigital Au electrodes has been tested as a H2 gas sensor. The resistance R estimated from the intersection of the semi-circle with the real axis in a complex-impedance plot was used as a sensing signal. H2 addition in a gas decreased the resistance. Pt–WO3/ZrO2 showed a higher response magnitude to H2 than WO3/ZrO2 and Pt/ZrO2. The sensor was found to respond consistently and rapidly to change in concentration of H2 in the oxygen rich and moist gas mixture at 120–150 °C. The conductivity of the device varied almost linearly with the H2 concentration from 0.25 to 1.25%. The rate constants (k) of Pt–WO3/ZrO2 for the response and recovery transients were 10 and 53 times higher than those of Pt/WO3, respectively. The response magnitude of Pt–WO3/ZrO2 to H2 was not markedly affected by changing the water vapor concentration from 1.0 to 3.4% and O2 concentration from 5 to 20%. The effect of WO3 loading of the Pt–WO3/ZrO2-based sensor combined with STEM and UV–vis results indicates that subnano-sized polytungstate clusters on the zirconia surface play an important role in the conductivity increase by H2 adsorption, which can be due to an increase in the number of acidic Hδ+ species on the polytungstate surface.