Set Of Interdigitated Electrodes Research Articles

Continuous-flow electrorotation (cROT): improved throughput characterization for dielectric properties of cancer cells.

This paper presents the concept of a newly developed high-throughput measurement device for determining the dielectric properties of cancer cells. The proposed continuous-flow electrorotation (cROT) device can induce electrorotation (ROT) with vertical rotation using two sets of interdigitated electrodes on the top and bottom substrates to torque the cells. In the developed device, multiple rotating cells flowing in a microchannel are aligned between electrodes using dielectrophoresis. This allows for the measurement of the rotational behavior of the cells with continuous flow, resulting in a significant improvement in throughput compared to the conventional ROT devices reported previously. The dielectric properties, permittivity of the cell membrane and conductivity of the cell cytoplasm, of HeLa cells obtained by simultaneous measurements using the developed cROT device were 9.13 ± 1.02 and 0.93 ± 0.10 S m-1, respectively. Moreover, the measurement throughput was successfully increased to 2700 cells per h using the cROT technique.

A microfluidic biosensor for rapid simultaneous detection of waterborne pathogens

A microfluidic based biosensor was investigated for rapid and simultaneous detection of Salmonella, Legionella, and Escherichia coli O157:H7 in tap water and wastewater. The biosensor consisted of two sets of focusing electrodes connected in parallel and three sets of interdigitated electrodes (IDE) arrays. The electrodes enabled the biosensor to concentrate and detect bacteria at both low and high concentrations. The focusing region was designed with vertical metal sidewall pairs and multiple tilted thin-film finger pairs to generate positive dielectrophoresis (p-DEP) to force the bacteria moving toward the microchannel centerline. As a result, the bacterial pathogens were highly concentrated when they reached the detection electrode arrays. The detection IDE arrays were coated with three different antibodies against the target bacterial pathogens and a cross-linker to enhance the binding of antibodies to the detection electrode. As the binding of bacterial pathogen to its specific antibodies took place, the impedance value changed. The results demonstrated that the biosensors were capable of detecting Salmonella, Legionella, and E. coli 0157:H7 simultaneously with a detection limit of 3 bacterial cells/ml in 30 − 40 min.

Fabrication of Aluminum Interdigitated Electrode for Biosensor Application Using Conventional Lithography

A simple technique for the fabrication of interdigitated electrode (IDEs) using conventional lithography was presented. A top-down simple lithography approach was used to fabricate a set of Interdigitated electrodes were patterned with aluminum metal. Silicon dioxide serves to isolate the electrode from the substrate. A chrome mask was proposed to complete this work. In this work, the proposed method was experimentally demonstrated by fabricating the IDEs structure 4-5μm, approximately. The dimensions of structure were determined by using scanning electron microscopy (SEM). It is a simple, easy-to-use and cost effective method and does not require complicated micro-lithography process for fabricating desired microelectrode in reproducible approach.

Evaluating the adhesion of SU-8 thin films using an AlN/Si surface acoustic wave sensor

A new approach is developed for evaluating the adhesion of SU-8 thin films using a surface acoustic wave (SAW) sensor. The SAW sensor consists of a silicon (Si) substrate coated with a thin aluminum nitride (AlN) film and two sets of inter-digital electrodes (IDT) patterned on the AlN surface. Two sensor configurations are developed in order to evaluate the adhesion of SU-8. In the first configuration the SU-8 layer is patterned on top of a gold film that is deposited on the AlN surface. In the second configuration the gold film is coated with an omnicoat layer prior to patterning the SU-8 film. Omnicoat is an adhesion promoter for SU-8, which is used to increase its adhesion to gold. The frequency responses from both configurations are measured and the shift in the center frequency value is evaluated. The results illustrate that without omnicoat the center frequency shifts to a higher value indicating an increase in the wave velocity. This is because the poor adhesion of the SU-8 layer without omnicoat causes the wave to be more concentrated in the AlN/Si structure and AlN has a higher acoustic wave velocity in comparison to the SU-8 layer. In addition, four SAW sensors operating at four different center frequencies are developed to investigate the change in sensor sensitivity with the increase in center frequency. The results indicate that the sensor sensitivity increases proportionally to the increase in operating frequency. Finally, a theoretical model is developed to calculate the wave dispersion profile for the SU-8/AlN/Si configuration. The interface of the SU-8/AlN layers is modeled as a layer of mass-less springs with stiffness K(N m−3). The shifts in the wave dispersion profile at different levels of interface spring stiffness are compared to the experimental values to evaluate the adhesion of the SU-8 layer.

PCR-based detection in a micro-fabricated platform

We present a novel, on-chip system for the electrokinetic capture of bacterial cells and their identification using the polymerase chain reaction (PCR). The system comprises a glass-silicon platform with a set of micro-channels, -chambers, and -electrodes. A platinum thin film resistor, placed in the proximity of the chambers, is used for temperature monitoring. The whole chip assembly is mounted on a Printed Circuit Board (PCB) and wire-bonded to it. The PCB has an embedded heater that is utilized for PCR thermal cycle and is controlled by a Lab-View program. Similar to our previous work, one set of electrodes on the chip inside the bigger chamber (0.6 microl volume) is used for diverting bacterial cells from a flowing stream into to a smaller chamber (0.4 nl volume). A second set of interdigitated electrodes (in smaller chamber) is used to actively trap and concentrate the bacterial cells using dielectrophoresis (DEP). In the presence of the DEP force, with the cells still entrapped in the micro-chamber, PCR mix is injected into the chamber. Subsequently, PCR amplification with SYBR Green detection is used for genetic identification of Listeria monocytogenes V7 cells. The increase in fluorescence is recorded with a photomultiplier tube module mounted over an epifluorescence microscope. This integrated micro-system is capable of genetic amplification and identification of as few as 60 cells of L. monocytogenes V7 in less than 90 min, in 600 nl volume collected from a sample of 10(4) cfu ml(-1). Specificity trials using various concentrations of L. monocytogenes V7, Listeria innocua F4248, and Escherichia coli O157:H7 were carried out successfully using two different primer sets specific for a regulatory gene of L. monocytogenes, prfA and 16S rRNA primer specific for the Listeria spp., and no cross-reactivity was observed.

Dielectrophoresis switching with vertical sidewall electrodes for microfluidic flow cytometry

A novel dielectrophoresis switching with vertical electrodes in the sidewall of microchannels for multiplexed switching of objects has been designed, fabricated and tested. With appropriate electrode design, lateral DEP force can be generated so that one can dynamically position particulates along the width of the channel. A set of interdigitated electrodes in the sidewall of the microchannels is used for the generation of non-uniform electrical fields to generate negative DEP forces that repel beads/cells from the sidewalls. A countering DEP force is generated from another set of electrodes patterned on the opposing sidewall. These lateral negative DEP forces can be adjusted by the voltage and frequency applied. By manipulating the coupled DEP forces, the particles flowing through the microchannel can be positioned at different equilibrium points along the width direction and continue to flow into different outlet channels. Experimental results for switching biological cells and polystyrene microbeads to multiple outlets (up to 5) have been achieved. This novel particle switching technique can be integrated with other particle detection components to enable microfluidic flow cytometry systems.

Dielectrophoretic Microfluidic Switching for Lab on a Chip Applications

AbstractDielectrophoresis switching with vertical microelectrodes in the side wall of microchannel have been designed, fabricated and tested. A set of interdigitated electrodes in the side wall of the microchannels is used for the generation of non-uniform electrical field to introduce DEP force to repel or attract beads/cells to the sidewalls. A countering DEP force is generated from another set of electrodes patterning on the opposing side walls. These DEP forces can be adjusted by the voltage and frequency applied. By manipulating the coupled DEP forces, the particles flowing through the microchannel can be positioned at different equilibrium points along the width direction and continue to flow into different outlets. The objects of interest can be switched to desired channel outlets in the flow with no need of any moving parts and the down-stream channel can be more than three outlets. Experimental results for switching cells to two outlets and polystyrene microbeads to five outlets have been achieved. The effect of the geometry and flow rate on the performance of the switching was studied and an analytical solution for the optimal design and operation of DEP electrode arrays has been derived from the proposed model.

OS17-2-2 Experimental characterization of Active Fiber Composites used as piezoelectric transducers for emitting and receiving Lamb waves in plate-like structures

Active Fiber Composites (AFC) consist of one layer of piezoelectric ceramic fibers embedded in an epoxy matrix and sandwiched between two sets of interdigitated electrodes. They show orthotropic mechanical properties due to their design and manufacturing. The small thickness and the conformability to curved surfaces make them suitable for applications in structural health monitoring (SHM) with acoustic nondestructive testing methods. The piezoelectric properties of the AFC allow for both actuation and sensing capabilities with the same element which enables emitting and receiving of structural waves (e.g., Lamb waves) for monitoring of critical structural elements. Before realizing specific applications for AFC in SHM systems, it is necessary to characterize the transfer behavior of AFC bonded on a structure for excitation and sensing of transient waves which propagate in the structure. To characterize this behavior experimentally, the acoustic wave field in a thin, planar structure excited from surface bonded AFC is explored with a laser interferometer. Surface velocities at different positions around an AFC bonded on an aluminum plate during transient excitation are recorded. The transfer function is calculated for different angles from the fiber direction of the AFC for both the first symmetric and the first antisymmetric Lamb wave mode. The sensing process is also investigated: structural waves generated by surface bonded piezoelectric ceramic discs are measured likewise with laser interferometry in the vicinity of the AFC and with the AFC itself. Results show, that the emitting and receiving capabilities of the AFC decrease with increasing angle from the fiber direction of the AFC. Typical maxima and minima in the transfer function depend on the length of the AFC.

Differential capacitive position sensor for planar MEMS structures with vertical motion

A capacitive sensor has been developed for measuring the vertical deflection of bridge-type micro-electromechanical (MEMS) silicon actuators. The sensor requires no electrodes above the actuator surface and does not require the actuator diaphragm to be used as a signal electrode. Sets of interdigitated electrodes, one for ac signal injection and the other for signal sensing, are placed beneath the actuator membrane. As the actuator deflects, the capacitance between the interdigitated finger electrodes is altered, leading to a change in the time-varying charge induced on the sense fingers. This change in induced charge is monitored by a current-to-voltage converter, thereby providing a measure of actuator displacement in the direction perpendicular to the silicon substrate. Signal voltages on the order of 10 mV per 1 μm of deflection are observed for deflections in the 1-μm range.

Dielectrometry measurements of moisture dynamics in oil-impregnated pressboard

In oil-impregnated pressboard of medium and low humidity the complex dielectric spectrum's shape and amplitude do not change with variations in temperature and moisture content, but only shift in frequency. Thus it is possible to create a 'universal' curve, with appropriate temperature correction factors, which can be used to extract information about the moisture dynamics of solid transformer insulation from dielectrometry measurements. To create the universal curve, measurements are taken with the material placed in a parallel-plate structure whose complex impedance is measured. To measure spatial distributions of dielectric properties, imposed /spl omega/-k (frequency-wavenumber) dielectrometry is used, where a set of interdigitated electrodes on one surface of the material cause the electric field to have a limited depth of penetration into the dielectric, proportional to the electrode spacing. Measurements using the parallel-plate methodology establish a mapping of the dielectric spectrum of EHV-Weidmann HIVAL pressboard impregnated with Shell Diala A transformer oil, as a function of temperature and water content. This mapping is then used to determine spatial moisture profiles in pressboard in other experiments which make use of a three-wavelength interdigitated sensor. >

A new type of pressure sensor utilizing surface acoustic waves

Abstract Mechanical strain effect experiments on a 103 MHz Y-Z LiNbO3 surface acoustic waves (SAW) transducer with 3 cm electrode distance have been made. The phase shift was 40 degrees at −90 × 10−6 strain and quite linear with strain. Optimum design considerations for a SAW pressure sensor consisting of a clamped edge piezoelectric diaphragm with two sets of interdigital electrodes have been made. The optimum positions for the electrodes were determined. Deflection of the diaphragm under pressure retards the phase for one set and advances the phase for the other set. The maximum phase shift and cancellation of thermal expansion effects results by measuring the phase difference between the two sets. The maximum phase shift and cancellation of thermal expansion effects results by measuring the phase difference between the two sets.