Enhancing the electrocoagulation process for harvesting marine microalgae (Tetraselmis sp.) using interdigitated electrodes

In previous our research, we introduced attachment or detachment of 25nm diameter quantum dots (QDs) manipulating method and 100nm diameter polystyrene (PS) nano-beads at nano sized metal structures by dielectrophoretic (DEP) force. The metal nano-structures were connected with micro electrode to apply the DEP force for trapping the nanoparticles. The DEP force is easily controllable by frequency and intensity of applied electric field. And the DEP force is very sufficient to manipulate the fluorescent nanoparticles at specific nanostructures, due to the large difference of electric fields inducement around nanostructures. The trapped fluorescent nanoparticles at nano metal structures which can be considered and called as a composited structure of photon emitting nanoparticles and nano structures could be utilized in study of coupling photons to plasmon waveguides as a real single photon generator. And the nanoparticle manipulating method could accomplish the additional composite structures without any chemical reactions as a lithographic method of fluorescent nanoparticles which can be used in QD display. The QDs are the most important and remarkable candidates nanoparticles to produce photon-emitting in quantum devices and display. However, the previous research had limitations such as limiting the variety of nanostructure, degree of freedom, and attaching sites due to the connected microelectrodes. And additional fabrication steps should be needed after the manipulation of nanoparticles to metal structures. In this paper, we introduced the manipulation of QD which is composed with cadmium selenide, the semiconducting materials at the nanostructures by DEP force for plasmonic applications and QD display. For the high degree of freedom, the nanostructures didn’t connect with microelectrodes. Various shapes of nano structures which is made of gold are accomplished between the micro electrodes. The microelectrodes were not connected with the nano-structures. Wire, Y-branch and vertex shape of nanostructure were fabricated with e-beam lithography and lift-off process. The distance between microelectrodes and nanostructures was also calculated to optimize the condition of QD trapping with multiphysics simulation. Possibility of selective manipulation of QDs was also performed through the theoretical approaches at various shape of nanostructures by using the DEP force. Each shape of structures was considered to manipulate the QDs at the nanostructures. The selective manipulation which is attaching-side, position, end-facet selective in nanostructures provide the three degrees of freedom in attachment in the same structure. Consequently, the semiconductor materials based fluorescent nanoparticles, QDs, are successfully manipulated at nano-structures without any connecting with microelectrodes.

A new technology of the electric-field manipulation by dielectric particles in dielectric liquids and drops has been developed in the last decades. To simulate electromechanics of microparticles in a weaklyconducting dielectric drop the Taylor's leaky-dielectric model is extended. To achieve this electric-potential distribution inside and outside a weakly-conducting dielectric sphere embedded in a weakly-conducting dielectric in an electric field is determined taking into account the interfacial current. The conventional definition of the total, bulk plus surface, conductance of the sphere is detailed allowing for its dependence on the angular distribution of the external electric field. Technology of microparticles moving over the interface of the drop is based on the application of electrohydrodynamic (EHD) drag and dielectrophoretic (DEP) forces. The surface conductivities of the drop and individual microparticles can have a significant influence on the surface charge and thereby on the DEP and EHD drag forces. Thus, we show that recent explanation of manipulation by microparticles trapped at the interface of a silicone-oil drop immersed in castor oil is misleading. Taking into account the surface conductivity of the microparticles, we find that EHD drag and DEP forces are of the same direction but not opposite at zero or low frequencies as stated previously. Due to the reversal of the DEP force with the field frequency the motion of microparticles turns back. Surface conductivity of the drop can also explain experiments in which the prolate deformation persists after liquids of the drop and ambient medium are interchanged.

Harvesting of Microalgae Using Electrocoagulation Process

Microalgae harvesting via pH induced flocculation along with utilization of recovered medium after flocculation is one of the most economical methods for separating the microalgal biomass in order to reduce the dewatering cost. In this study, optimization of marine and freshwater microalgae flocculation by pH adjustment was investigated via central composite design methodology. One molar of KOH and NaOH solutions were used to increase the pH level of the microalgal culture. Increasing pH value of the medium provided the highest flocculation efficiency up to 92.63 and 86.18% with pH adjusted to 10.5 with KOH and NaOH solutions for marine microalgae Nannochloropsis oculata and freshwater microalgae Chlorella minutissima, respectively. Also, it was revealed that microalgae cells were still alive after flocculation process and their biochemical composition was not changed, and flocculated medium can be used again for the next microalgal production. According to the results, it can be said that this method is cheap and effective, simple to operate and provides the utilization of flocculated medium again.

A new control mechanism to realize tunable microsphere resonators suspended in liquid is proposed. Via adjusting the bias voltage across an inhomogeneous dielectric structure (a rib waveguide plus microsphere), the microsphere resonator is attracted and levitated on top of the single-mode rib waveguide via an repulsive dielectrophoretic (DEP) force, where the coupling gap between the microsphere resonator and the waveguide is precisely controlled. The tunable gap spacing is analyzed by calculating the dielectrophoretic force through Maxwell stress tensor.

The research in this paper extends previous liquid film flow boiling studies by including the effect of an additional electrohydrodynamic (EHD) force, namely the dielectrophoretic (DEP) force. Rather than using only EHD conduction pumping of the liquid film to electro-wet the heater surface, a localized non-uniform electric field above the heater surface is also used to generate a dielectrophoretic force for improved vapor bubble extraction during the nucleate boiling regime. The effect of liquid film height and applied potential are studied as a function of heater superheat and heat flux. The study considers the sole and combined effect of DEP with EHD conduction pumping. A brief analytical study is also used to estimate the expected dielectrophoretic force magnitude and explain the results. All of the above studies are also used to quantify the enhancement in heat transfer that can be achieved when heat transport systems are driven or augmented by these electrohydrodynamic phenomena. The results show remarkable enhancement of up to 1217% in heat flux and boiling heat transfer coefficient for a given superheat when both mechanisms are used simultaneously. The experimental data are important for applications in thermal management in terrestrial and micro-gravity conditions.

A major problem for analysis of bio-nanoparticles such as the influenza viruses (size is about 100 nm) is that sample concentration is low. We developed manipulation of the single virus using optical tweezers supported by dielectrophoretic concentration of the viruses in a microfluidic chip. The microfluidic chip made of poly (dimethyl siloxane) (PDMS) is useful to achieve stable manipulation of the virus. The chip has the independent sample chamber and analysis chamber to make the quantitative analysis of the functions of the virus before and after infection to the target cell. Dielectrophoretic (DEP) force worked inside the sample chamber concentrates the virus. DEP force was also worked for avoiding virus adhesion to the glass substrate. Concentrated virus was flown to the sample selection part and was trapped by optical tweezers. Trapped virus was transported to the analysis chamber and contact to the target cell for infection. In this paper, we described the DEP virus concentration for single virus infection to a specific cell. We succeeded in the DEP concentration of the influenza virus, transport of the single virus transport, and contact to the specific H292 cell.

The behaviors of a single droplet and bubble in dielectric liquid on which the dielectrophoretic (DEP) force was imposed, were studied. It is possible to apply the DEP force to the bubble elimination device under the reduced gravity condition because the bubbles could be moved without contact or disturbance by the DEP force. It was shown that the A. C. (alternating current) electrical field is more preferable than the D. C. (direct current) one because the effect of the electrophoretic (EP) force, whose strength is not definite, is often considerable under the D. C. electrical field. Furthermore, it was observed that the droplets and bubbles in the dielectric liquid moved along a straight path under the nonhomogeneous A. C. field. One-dimensional motion of a single bubble was analytically investigated by solving equation of the motion for the bubble. It was shown that the experimental results were consistent with analytical ones in the region where the electric field was strong.

Living cells have evolved sophisticated signaling networks allowing them to respond to a wide array of external stimuli. Microfluidic devices, facilitating the analysis of signaling networks through precise definition of the cellular microenvironment often lack the capacity of delivering multiple combinations of different signaling cues, thus limiting the throughput of the analysis. To address this limitation, we developed a microfabricated platform combining microfluidic definition of the cell medium composition with dielectrophoretic definition of cell positions and protein microarray-based presentation of diverse signaling inputs. Ligands combined at different concentrations were spotted along with an extracellular matrix protein onto a glass substratum in alignment with an electrode array. This substratum was combined with a polydimethylsiloxane chip for microfluidic control of the soluble medium components, in alignment with the electrode and protein arrays. Endothelial cells were captured by dielectrophoretic force, allowed to attach and spread on the protein spots; and the signaling output of the NF-kappaB pathway in response to diverse combinations of IGF1 and TNF was investigated, in the absence and presence of variable dose of the pathway inhibitor. The results suggested that cells can be potently activated by immobilized TNF with IGF1 having a modulating effect, and the response could be abolished to different degrees by the inhibitor. This study demonstrates considerable potential of combining precise cell patterning and liquid medium control with protein microarray technology for complex cell signaling studies in a high-throughput manner.

Electro coagulation process using various deigns and configurations have been tested from time to time and found to impart major role in the process. Mostly non rotating configurations were used in the available literature. The usage of rotating electrode reactors has come to light and found out to be effective configuration. The effect of rotating and non rotating reactor configurations along with other affecting parameters likes current density, detention time and energy consumption were investigated. Set of experiments were conducted using simulated sample prepared by dissolving basic red dye in tap water to carry out the performance evaluation of the two type of reactors configuration. A comparative study between the two configurations was made to investigate their effectiveness in term of COD removal efficiency and economics of treatment. The results show that rotating reactor configuration have consumed 15-17% less energy for maximum COD removal of 96.40% and thus have better removal efficiency and lower specific energy consumption than non rotating reactor configuration.

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.

Effective harvesting of low surface-hydrophobicity microalgae by froth flotation

Fabrication and electrochemical properties of an interdigitated array electrode in a microfabricated wall-jet cell

Micro-structured electrode (MSE) arrays allow the generation of large-area uniform glow discharges over a wide pressure range up to atmospheric pressure. The electrode widths, thicknesses and distances in the micrometre range are realized by means of modern micro-machining and galvanic techniques. The electrode distance, the gap width d, is small enough to generate sufficiently high electric field strengths to ignite gas discharges by applying only moderate radio frequency (RF, 13.56 MHz) voltages (80–390 V in Ne, He, Ar, N2 and air). The non-thermal plasma system is characterized by a special probe measuring the electric parameters. We tested MSE arrays with d = 70, 25 and 15 µm. The MSE driven plasmas show a different behaviour from conventional RF discharge plasmas. Due to the very small electrode gap width we can describe the behaviour of the charged particles in the RF field of our system with the dc Townsend breakdown theory, depending on the pressure range and gas. With decreasing pressure, the gas discharges, especially in Ne and He, are increasingly dominated by field electron emission. With the MSE arrays as plasma sources several applications were developed and successfully tested, e.g. decomposition of waste gases and sterilization of food packaging materials at atmospheric pressure.

Separation is a crucial step in the analysis of living microparticles. In particular, the selective microseparation of phytoplankton by size and shape remains an open problem, even though these criteria are essential for their gender and/or species identification. However, microseparation devices necessitate physical membranes which complicate their fabrication, reduce the sample flow rate and can cause unwanted particle clogging. Recent advances in microfabrication such as High Precision Capillary Printing allow to rapidly build electrode patterns over wide areas. In this study, we introduce a new concept of membrane-less dielectrophoretic (DEP) microseparation suitable for large scale microfabrication processes. The proposed design involves two pairs of interdigitated electrodes at the top and the bottom of a microfluidic channel. We use finite-element calculations to analyse how the DEP force field throughout the channel, as well as the resulting trajectories of particles depend on the geometry of the system, on the physical properties of the particles and suspending medium and on the imposed voltage and flow rates. We numerically show that in the negative DEP regime, particles are focused in the channel mid-planes and that virtual pillars array leads either to their trapping at specific stagnation points, or to their focusing along specific lines, depending on their DEP mobility. Simulations allow to understand how particles can be captured and to quantify the particle separation conditions by introducing a critical DEP mobility. We further illustrate the principle of membrane-less DEP microseparation using the proposed setup, by considering the separation of a binary mixture of polystyrene particles with different diameters, and validate it experimentally.