Dielectrophoretic Method Research Articles

Anisotropic micro-cloths fabricated from DNA-stabilized carbon nanotubes: one-stop manufacturing with electrode needles.

Among a variety of solution-based approaches to fabricate anisotropic films of aligned carbon nanotubes (CNTs), we focus on the dielectrophoretic assembly method using AC electric fields in DNA-stabilized CNT suspensions. We demonstrate that a one-stop manufacturing system using electrode needles can draw anisotropic DNA-CNT hybrid films of 10 to 100 µm in size (i.e., free-standing DNA-CNT micro-cloths) from the remaining suspension into the atmosphere while maintaining structural order. It has been found that a maximal degree of polarization (ca. 40%) can be achieved by micro-cloths fabricated from a variety of DNA-CNT mixtures. Our results suggest that the one-stop method can impart biocompatibility to the downsized CNT films and that the DNA-stabilized CNT micro-cloths directly connected to an electrode could be useful for biofuel cells in terms of electron transfer and/or enzymatic activity.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-0817-3) contains supplementary material, which is available to authorized users.

Cell patterning using a dielectrophoretic–hydrodynamic trap

The paper presents a dielectrophoretic method for cell patterning using dielectrophoretic–hydrodynamic trap. A distinctive characteristic of the device is that the dielectrophoretic (DEP) force is generated using a structure that combines conventional electrode-based DEP (eDEP) with insulator-based DEP method (iDEP). The conventional eDEP force is generated across the microfluidic channel between a top plate indium tin oxide electrode and a thin CrAu electrode. Meantime, an isolating cage built from SU8 photoresist around the thin electrode modifies the electric field generating an iDEP force. The cells that are flowing through a microfluidic channel are trapped in the SU8 cage by the total DEP force. As a result, according to the cell dimension and the thickness of the SU8 layer, different cell patterns can be achieved. If the cell’s size is sensitively smaller than the dimensions of the hydrodynamic trap, due to the dipole–dipole interaction, the cell can be organized in 3D structures. The trapping method can be used for conducting genetic, biochemical or physiological studies on cells.

A dielectrophoretic method of discrimination between normal oral epithelium, and oral and oropharyngeal cancer in a clinical setting.

Despite the accessibility of the oral cavity to clinical examination, delays in diagnosis of oral and oropharyngeal carcinoma (OOPC) are observed in a large majority of patients, with negative impact on prognosis. Diagnostic aids might help detection and improve early diagnosis, but there remains little robust evidence supporting the use of any particular diagnostic technology at the moment. The aim of the present feasibility first-in-human study was to evaluate the preliminary diagnostic validity of a novel technology platform based on dielectrophoresis (DEP). DEP does not require labeling with antibodies or stains and it is an ideal tool for rapid analysis of cell properties. Cells from OOPC/dysplasia tissue and healthy oral mucosa were collected from 57 study participants via minimally-invasive brush biopsies and tested with a prototype DEP platform using median membrane midpoint frequency as main analysis parameter. Results indicate that the current DEP platform can discriminate between brush biopsy samples from cancerous and healthy oral tissue with a diagnostic sensitivity of 81.6% and a specificity of 81.0%. The present ex vivo results support the potential application of DEP testing for identification of OOPC. This result indicates that DEP has the potential to be developed into a low-cost, rapid platform as an assistive tool for the early identification of oral cancer in primary care; given the rapid, minimally-invasive and non-expensive nature of the test, dielectric characterization represents a promising platform for cost-effective early cancer detection.

One pot, single step, room temperature dielectrophoretic deposition of gold nanoparticles clusters on polyethylene terephthalate substrate

The major challenge of plastic electronics is the deposition of gold nanoparticles (AuNPs) on flexible substrates at room temperature. Here, we show fast, single step, room temperature deposition of AuNPs on polyethylene terephthalate (PET) and biaxially oriented PET (BoPET) substrate by employing dielectrophoresis. The deposition has been carried out using two-electrode system, with BoPET (or PET) and metallic (Pt or stain steel) mesh, under an AC signal of 20 kHz and 20 V peak-to-peak (V(pp)) (signal for PET is 6 V(pp) and 6 kHz). In this method, we show how to deposit AuNPs on PET-like insulator by exploiting its polarization capability under an AC signal. The polarization of PET has been confirmed by change in the Raman spectra of the PET film under in situ AC signals. Furthermore, we show that using this dielectrophoretic deposition method, the PET films can be patterned by AuNPs at room temperature without any pre- and posttreatment.

Preface to Special Topic: Microfluidics in Cancer Research

Preface to Special Topic: Microfluidics in Cancer Research

Dielectrophoretic self-assembly of polarized light emitting poly(9,9-dioctylfluorene)nanofibre arrays

Conjugated polymer based 1D nanostructures are attractive building blocks for futureopto-electronic nanoscale devices and systems. However, a critical challenge remains thelack of manipulation methods that enable controlled and reliable positioning andorientation of organic nanostructures in a fast, reliable and scalable manner. To addressthis challenge, we explore dielectrophoretic assembly of discrete poly(9,9-dioctylfluorene)nanofibres and demonstrate site selective assembly and orientation of these fibres.Nanofibre arrays were assembled preferentially at receptor electrode edges, beingaligned parallel to the applied electric field with a high order parameter fit (∼0.9) and exhibiting an emission dichroic ratio of ∼ 4.0. As such, the dielectrophoretic method represents a fast, reliable and scalableself-assembly approach for manipulation of 1D organic nanostructures. The abilityto fabricate nanofibre arrays in this manner could be potentially important forexploration and development of future nanoscale opto-electronic devices and systems.

Electrical and optical characterization of GaN micro-wires

A near atmospheric pressure solution growth process was developed to produce an abundant quantity of GaN micro-wires in the c-direction with a length of tens of microns and a diameter of approximately 1–10 μm. Raman analysis showed that the micro-wires were free of stress which was expected for a free-forming crystal. The lack of stress and extended defects in the GaN micro-wire provided a useful test-bed to directly compare the wet-etch behavior of the polar c-planes and non-polar m-planes in GaN. The etch behavior at the end of the micro-wire (±c) was dramatically different, with the (0 0 0 1) plane found to be stable and the (0 0 0 −1) plane observed to rapidly etch into nanoscale hexagonal pyramids. Additionally a dielectrophoretic method was employed to readily align the wires as part of a larger device processing sequence.

Functional Microscopy Tip Fabrication by an Electric Conductive Nanowire

The functional microscopy tip was fabricated by an electric conductive nanowire (NW). Single crystalline nickel silicide (NiSi) NW grown by plasma-enhanced chemical vapor deposition has an excellent electrical conductivity. On behalf of the advantages in tiny size and conductivity of NiSi NW, it was utilized as a nanoscale probe. Dielectrophoretic method was applied to position the NW. The NiSi NW containing solution was dropped in an ac electric field applying system to align the NiSi NW on a Si cantilever. The fabricated NiSi NW-sitting functional microscopy tip obtained the information of topography and electrical signals from a nanoscale structure. It shows the high potential of nanoscale microscopy tip fabrication at reduced processing steps.

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.

Restoring electrical conductivity of dielectrophoretically assembled graphite oxide sheets by thermal and chemical reduction techniques

Thin layers of graphite oxide sheets were dispersed in dimethylformamide and dielectrophoretically assembled onto predefined and opposing metal electrodes. The dielectrophoretic method resulted in the deposition of multiple layers of graphite oxide. After drying, the deposits were then reduced by thermal or chemical methods. Raman spectroscopy and electrical transport measurements revealed that the thermal reduction technique was more effective in restoring electrical conductivity than the chemical reduction method.

A nickel silicide nanowire microscopy tip obtains nanoscale information

An electric conductive Ni silicide nanowire (NiSi NW) embedding electric forcemicroscopy (EFM) tip was fabricated by the dielectrophoretic method and was used toobtain electric information. Due to the geometric and electric excellence, theNiSi NW provides advantages in imaging and fabrication of the microscopy tip.A lead zirconate titanate (PZT) ferroelectric thin film was positively and negativelypolarized, and the polarities were obtained by probing of the NiSi NW EFM tip to givedistinctive charging information of the PZT film. Moreover, the NiSi NW EFM probing wasadopted to achieve the electrical signal from the NW interconnect. The NiSi NW EFMprobe confirmed the uniform electric-potential distribution through the NiSi NWinterconnect with a small standard deviation. This demonstrates the feasibility offunctional utilizations of the NiSi NW.

Collection, Measurement and Treatment of Microorganism Using Dielectrophoretic Micro Devices

Constant monitoring of manufacturing processes has been essential in food industry because of global expansion of microbial infection. Micro-scale dielectrophoretic method is an attractive technique for direct operation and quantitative detection of bioparticles. The electrical system is capable of rapid and simple treatments corresponding to severe legal control for food safety. In this paper, newly developed techniques are reviewed for bacterial concentration, detection and sterilization using dielectrophoresis in a micro reactor. The perspective to an integrated micro device of those components is also discussed.

Dielectrophoretic oocyte selection chip for in vitro fertilization

This paper reports a new dielectrophoretic separation method of porcine oocytes for in vitro fertilization. Conventional manual selection of oocyte highly depends on the expert's experience and lacks universal standards for identifying the quality of oocyte. In this study, an electrode array chip with castellated shape was developed to evaluate dielectrophoretic velocities of oocytes, under applied bias conditions with an AC 3 V waveform at 1 MHz for 15 s. Based on different dielectrophoresis (DEP) response, the selected group of oocytes that moved showed a better developmental potential than the group of oocytes that stayed, representing a higher rate of blastocyst formation and a lower rate of polyspermic fertilization. In addition, the overall developmental potential of oocytes selected by the DEP device was comparable to that of oocytes selected by conventional manual method. These results demonstrate that the difference in dielectrophoretic velocity can be used to establish an objective criterion for the selection of oocytes. Consequently, this method will open the possibility to develop an automatic tool for oocyte selection, which would be helpful for assisted reproductive technologies such as transgenic and clonal animal production.

A Dielectrophoretic Method for High Yield Deposition of Suspended, Individual Carbon Nanotubes with Four-Point Electrode Contact

We have investigated new methods to manufacture four-point contacted suspended, individual multiwalled carbon nanotubes by dielectrophoresis. The necessity of four-point contacted carbon nanotubes is underpinned by the need for more exact measurements of carbon nanotube properties and more complex carbon nanotube based devices. In the experimental study herein, we first evaluated the most important dielectrophoretic parameters of two-point electrode structures. The knowledge gained from this step was applied to the deposition of suspended, individual multiwalled carbon nanotubes over two different four-point electrode designs, a 2-D chip design and a novel 3-D chip design. Our results show that the novel approach using three dimensions for the chip design is superior to the current state of the art 2-D designs. We report a highly improved deposition yield of carbon nanotubes over 3-D chips, which will facilitate the reliable design and manufacturing of future carbon nanotube-integrated devices.

Bias modulated highly sensitive NO2 gas detection using carbon nanotubes

A NO2 gas sensor of carbon nanotubes (CNT) array was fabricated by a dielectrophoretic method. It is the first report of 50 ppb level detection operating at room temperature without a supplementary assistance of a heating system, vacuum environment, metal decoration, or additional film coating. The as-deposited CNTs on Pt electrodes by dropping of a CNT cropped solution provided good contact formation without post contact treatment. The bias voltage modulation improved the sensor performance by controlling the Schottky barrier potential. It is highly sensitive NO2 detection at room temperature, which may benefit to reduce the fabrication steps and cost as well.

Dielectrophoretic separation of biological samples in a 3D filtering chip

A field-flow dielectrophoretic separation method in a 3D filtering chip has been developed in this work. The separation method was possible due to the special configuration of the DEP filtering chip, which has a structure similar to a classical capacitor with two parallel plate electrodes (realized by using a stainless steel mesh) and a dielectric medium (defined by a suspension of 100 µm diameter silica beads in buffer solution). The dielectrophoretic phenomenon is generated by the non-uniformities of the dielectric media, which produce a gradient of the electric field and, as a consequence, a DEP force. If a suspension medium with cells flows through the filter, the DEP force can trap these cells around the contact points between the silica beads (if the cells exhibit positive DEP) or they are repelled into the space between the beads (if the cells exhibit negative DEP). It is shown that for two different cell populations, the frequency of the electric field and permittivity of the media can be tuned in such a way that one population will exhibit positive DEP and the other one negative DEP. The population that expresses negative DEP can be easily flushed out due to the hydrodynamic force which is larger at the center point between the beads. In such a way two cell populations can be separated. The working principle was verified with both live and dead yeast cells. Best results for the separation of viable and nonviable cell populations were achieved at an applied voltage of 150 V in a frequency range between 10 kHz and 20 kHz for flow rates of 0.1 ml min−1 and 0.2 ml min−1. With a few of these devices cascaded in series, higher efficiency could be achieved. As a result, this device and the associated proposed separation method can be very useful tools for bio-pharmaceutical industries since continuous flow separation at relatively high flow rates is both time and cost saving.

Electrical characteristics of single and doubly connected Ni silicide nanowire grown by plasma-enhanced chemical vapor deposition

Ni silicide nanowires were grown by plasma-enhanced chemical vapor deposition at 350°C. Transmission electron microscope analysis showed that Ni silicide nanowire has a single crystalline Ni3Si2 structure. The nanowire alignment was controlled by dielectrophoretic method and two nanowires were placed onto Pt electrodes under an ac biasing of 10Vp-p at 100kHz. The electric characteristics of the nanowire were obtained from double connection and single connection of 5.07 and 10.44kΩ, respectively. The resistivity values were obtained to be 183 and 208μΩcm, showing a uniform performance of the connection.

Continuous field-flow separation of particle populations in a dielectrophoretic chip with three dimensional electrodes

This letter presents a dielectrophoretic (DEP) separation method of particles under continuous flow. The method consists of flowing two particle populations through a microfluidic channel, in which the vertical walls are the electrodes of the DEP device. The irregular shape of the electrodes generates both electric field and fluid velocity gradients. As a result, the particles that exhibit negative DEP can be trapped in the fluidic dead zones, while the particles that experience positive DEP are concentrated in the regions with high velocity and collected at the outlet. The device was tested with dead and living yeast cells.

Extraction of semiconducting CNTs by repeated dielectrophoretic filtering

We have separated semiconducting carbon nanotubes from as-grown batch material (HiPco production). A special configuration of electrodes which generates a 3-dimensional electric field gradient was used to filter out and deposit metallic carbon nanotubes by the dielectrophoretic method, leaving the remaining dispersion enriched in semiconducting nanotubes. The efficiency of filtering was determined by Raman spectroscopy. Using repeated deposition cycles, the ratio of semiconducting to metallic tubes was increased. After seven cycles, the proportion of semiconducting tubes in the remaining dispersion reached 94%.

Effects of Dielectrophoretic Parameters on Fabrication and Electronic Properties of Single-Walled Carbon Nanotube Devices

AbstractWe recently developed a novel floating-potential dielectrophoretic method to selectively position individual single-walled carbon nanotubes between two floating electrodes while the bundles of nanotubes and impurities were attracted into the region between two control electrodes. In this study, we investigated effects of several process parameters including electric field distribution, electric field frequency, and solution media in order to understand the physical mechanisms of this dielectrophoretic process and to improve its efficiency. Results showed that both the magnitude and the direction of electrical force applied onto the nanotubes can be tailored by changing these process parameters. It was found that a 1 wt% sodium dodecyl sulfate in deionized water is an efficient solution for separating bundles of nanotubes into individual nanotubes and aligning individual nanotubes with a clean surface between two electrical contacts in comparison to N,N-dimethylformamide, 1,2-dichloroethane, 1,2-dichlorobenzene, 1,1-dichloromethane, ethanol, and isopropanol solutions. The fabricated carbon nanotube devices exhibit electronic properties comparable to nanotube transistors and interconnects fabricated by other methods.