Integratable non-clogging microconcentrator based on counter-flow principle for continuous enrichment of CaSki cells sample

This study addresses the need to reduce the risk of clogging when preparing samples for cell concentration, i.e., the CaSki Cell-lines (epidermoid cervical carcinoma cells). Aiming to develop a non-clogging microconcentrator, we proposed a new counter-flow concentration unit characterized by the directions of penetrating flows being at an obtuse angle to the main flow, due to employment of streamlined turbine blade-like micropillars. Based on the optimization results of the counter-flow unit profile, a fractal arrangement for the counter-flow concentration unit was developed. A counter-flow microconcentrator chip was then designed and fabricated, with both the processing layer and collecting layer arranged in terms of the honeycomb structure. Visualized experiments using CaSki cell samples on the microconcentrator chip demonstrated that no cell-clogging phenomena occurred during the test and that no cells were found in the final filtrate. The test results show an excellent concentration performance for the microconcentrator chip, while a concentrating ratio of >4 with the flow rate being below 1.0 ml/min. As only geometrical structure is employed in the passive device, the counter-flow microconcentrator can be easily integrated into advanced microfluidic systems. Owing to the merit of non-clogging and continuous processing ability, the counter-flow microconcentrator is not only suitable for the sample preparation within biomedical field, but also applicable in water-particle separation.     

Improved particle concentration by cascade AC electroosmotic flow

The importance of electrokinetics in microfluidic technology has been growing owing to its versatility and simplicity in fabrication, implementation, and handling. Alternating-current electroosmosis (ACEO), which is the motion of fluid due to the ion movement by an interaction between AC electric field and an electrical double layer on the electrode surface, has a potential for a particle concentration method to detecti rare samples flowing in a microchannel. This study investigates an improved ACEO-based particle concentration by cascade electrokinetic approach. Flow field induced by ACEO and accumulation behavior of particles were parametrically measured to discuss the concentrating mechanism. The accumulation of particles by ACEO can be explained by a balance between the attenuating electroosmotic flow to transport particles and the inherent diffusive motion of the particles, which is hindered due to the near-wall location. Although a parallel double-gap electrode geometry enables particles to be collected at the center of electrode very sharply, it has scattering zones with accumulated particles at sidewalls of the channel. This drawback can be overcome by applying sheath flow or introducing cascade electrode pattern upstream of the focusing zone. As a result, total concentration efficiency was 98.4 % for all the particles flowing in the cascade device. The resultant concentrated particles exist on the electrode surface within 5 μm, and three-dimensional concentration of particle with the concentration factor as large as 700 is possible using a monolithic channel, co-planar electrode, and sheathless solution feeding. This cascade electrokinetic method provides a new and effective preconcentrator for ultra-sensitive detection of rare samples.     

A microfluidic device for rapid concentration of particles in continuous flow by DC dielectrophoresis

This article presents a microfluidic device (so called concentrator) for rapid and efficient concentration of micro/nanoparticles using direct current dielectrophoresis (DC DEP) in continuous fluid flow. The concentrator is composed of a series of microchannels constructed with PDMS-insulating microstructures to focus efficiently the electric field in the flow direction to provide high field strength and gradient. Multiple trapping regions are formed within the concentrator. The location of particle trapping depends on the strength of the electric field applied. Under the experimental conditions, both streaming movement and DEP trapping of particles simultaneously take place within the concentrator at different regions. The former occurs upstream and is responsible for continuous transport of the particles, whereas the latter occurs downstream and rapidly traps the particles delivered from upstream. The observation agrees with the distribution of the simulated electric field and DEP force. The performance of the device is demonstrated by successfully and effectively concentrating fluorescent nanoparticles. At the sufficiently high electric field, the device demonstrates a trapping efficiency of 100%, which means downstream DEP traps and concentrates all (100%) the incoming particles from upstream. The trapping efficiency of the device is further studied by measuring the fluorescence intensity of concentrated particles in the channel. Typically, the fluorescence intensity becomes saturated in Trap 1 by applying the voltage (400 V) for >2 min, demonstrating that rapid concentration of the nanoparticles (10⁷ particles/ml) is achieved in the device. The microfluidic concentrator described can be implemented in applications where rapid concentration of targets is needed such as concentrating cells for sample preparation and concentrating molecular biomarkers for detection.     

Enhancing microcantilever capability with integrated AC electroosmotic trapping

Microcantilevers are finding wide applications in detecting biochemical agents. However, their usage has been limited to highly concentrated samples to ensure sufficient deposition of agents onto cantilevers. A pre-concentration or enrichment step will expand their application range to more dilute, practical samples and real-time detection. This paper reports the integration of in-situ particle concentrators on microcantilevers. Only a thin metal layer on microcantilevers is required to generate microfluidic convection of particles from solution bulk onto microcantilever surfaces, greatly enriching local particle counts and enhancing sensitivity of the system. A working prototype is presented in the paper. Preliminary experiments concentrating latex particles were conducted and the particle concentration effect has been experimentally verified using AFM probes as microcantilevers. As ACEO concentrator has no dependence on particle properties, the method is expected to be applicable to bio-particles collection.     

Sub-100-nm ROM pattern readout using a triangular protruded aperture mounted optical head slider

The continual advancement of the digital network society demands higher density and higher data transfer rates for all sorts of data storage. Optical memory based on the “near-field” principle is considered one of the most promising ones because it has no apparent physical density limit such as that due to the thermal instability encountered in magnetic recording. In light of this, we have previously demonstrated the superior readout performance of an optical head slider which is mounted on a non-circular aperture, specifically a triangular aperture having a bottom side size of 330 nm irradiated by polarized light, with this scheme indicating a clear signal response corresponding to a 70-nm-long single slit pattern. In order to fully realize the superior potential of the triangular aperture’s high spatial resolution and high signal output, it is essential to minimize aperture-to-medium spacing. In this paper, we introduce a protruded aperture mounted on a 1.5-mm-long miniaturized optical head slider whose aperture protrudes approximately 20 nm from an air-bearing surface level based on nano-step lithography technology. Utilizing a triangular aperture of 140 nm per side, a readout experiment was carefully performed at an aperture-to-medium spacing down to approximately 30 nm, corresponding to a circumferential velocity of 2.18 m/s. The influence of the incident light’s polarization direction (in relation to the bottom side of the triangular aperture) on the readout signals was evaluated by flying the aperture above a chromium patterned medium having single-space or line-and-space patterns whose line lengths ranged from 300 to 50 nm.     

Improved concentration and separation of particles in a 3D dielectrophoretic chip integrating focusing, aligning and trapping

This article presents a dielectrophoresis (DEP)-based microfluidic device with the three-dimensional (3D) microelectrode configuration for concentrating and separating particles in a continuous throughflow. The 3D electrode structure, where microelectrode array are patterned on both the top and bottom surfaces of the microchannel, is composed of three units: focusing, aligning and trapping. As particles flowing through the microfluidic channel, they are firstly focused and aligned by the funnel-shaped and parallel electrode array, respectively, before being captured at the trapping unit due to negative DEP force. For a mixture of two particle populations of different sizes or dielectric properties, with a careful selection of suspending medium and applied field, the population exhibits stronger negative DEP manipulated by the microelectrode array and, therefore, separated from the other population which is easily carried away toward the outlet due to hydrodynamic force. The functionality of the proposed microdevice was verified by concentrating different-sized polystyrene (PS) microparticles and yeast cells dynamically flowing in the microchannel. Moreover, separation based on size and dielectric properties was achieved by sorting PS microparticles, and isolating 5 μm PS particles from yeast cells, respectively. The performance of the proposed micro-concentrator and separator was also studied, including the threshold voltage at which particles begin to be trapped, variation of cell-trapping efficiency with respect to the applied voltage and flow rate, and the efficiency of separation experiments. The proposed microdevice has various advantages, including multi-functionality, improved manipulation efficiency and throughput, easy fabrication and operation, etc., which shows a great potential for biological, chemical and medical applications.     

AC electrokinetic pumping on symmetric electrode arrays

AC electro-osmotic (ACEO) pumping is experimentally demonstrated on a symmetric gold electrode array. Using asymmetric connection of electrodes to the applied AC voltage, spatial asymmetry along the array is created, which produces unidirectional flow of electrolyte. An aqueous solution of 100 μM KCl is selected as the pumping fluid. The liquid velocity obtained as a function of voltage and frequency is compared to that generated using travelling-wave electroosmosis (TWEO) with the same electrode array. The expected velocities from the linear electrokinetic models of ACEO and TWEO are computed numerically. The comparison shows that TWEO generates greater velocity amplitudes and the streamlines are smoother than those generated by ACEO.     

Droplet transport through dielectrophoretic actuation using line electrode

We explore a novel transverse line electrode configuration for droplet transport through dielectrophoretic actuation with potential lab-on-chip applications. Using a lumped electromechanical model, we show a weak dependence of DEP actuation force on electrode spacing in this configuration. The configuration successfully triggers translational drop motion with minimal changes in contact angle at considerably low voltages. Two sessile, deionized water drops placed horizontally apart on a indium-tin–oxide-coated glass with additional coatings of polydimethylsiloxane, and a thin layer of Teflon is merged by applying an AC field (88 V_rms at 150 kHz) through a common horizontal wire electrode. A lateral motion of two drops is induced along the horizontal electrode, eventually leading to coalescence. The drop motion is unique compared to electrowetting in its near-constant dynamic contact angle, and irreversibility on withdrawal of electric field. The effect of frequency on the drop behavior is examined through a parametric study on single drops within the range of 2–200 kHz. It is interesting to observe a switch-over from DEP behavior at high frequency to EWOD behavior at low frequency around a critical frequency (Jones in Langmuir 18:4437–4443, 2002).     

A novel movable electrode for realizing deep sub-micrometer gap in SOI-based MEMS square resonator

A novel movable electrode is demonstrated to realize deep sub-micrometer resonator-to-electrode gap. This design is based on SOI progress for better reducing the motional impedance. The movable structure contains two main beams, which can be actuated by DC voltage to realize lock-up. After the lock-up process, the DC voltage could be released, so this lock-up progress only needs to be implemented once and can be accomplished before encapsulation. The DC bias voltage for the resonator is thus reduced for better application. In order to examine the improvement of motional impedance using this structure, a 70 MHz lame-mode square resonator is employed in this study. The resonator-to-electrode gap is reduced from 1.05 μm to 50 nm, thus brings about a 280 Ω motional impedance, which is 157,000× smaller than that before the actuation of the movable structure. In addition, the capability to be realized in conventional SOI progress facilitates the fabrication process as well as the realization of high yield.     

Purification of a droplet using negative dielectrophoresis traps in digital microfluidics

The development of techniques for manipulating particles and integrating them into the digital microfluidic (DMF) devices has been the subject of several studies in recent years. This paper presents a dielectrophoretic-based method that uses triangular traps to manipulate particles and purify a droplet in DMF platforms. Numerical and experimental studies are conducted to show the effectiveness of the proposed trap geometry which is also compatible with the other operators in the DMF platform. The triangular trap geometry is used to move the polystyrene particles to one side of the trap using negative dielectrophoresis (nDEP). The droplet is then split into two smaller droplets with very low and high concentrations of particles using the electrowetting on dielectric technique. The average velocity of the particles (as they move along the trap) as a function of the vertex angle of the triangular trap and the gap between the top and bottom plate is examined. It is observed that the vertex angle of the trap plays more important role on the motion of the particles than the gap. Thus, to enhance the motion of the particles and minimize the effect of splitting on the purification process, the vertex angle and the slope of the side arms of the triangular trap are modified based on the results of the numerical model simulating the dielectrophoretic force on the particle. The enhanced geometry is fabricated and tested experimentally to show the effectiveness and ease-of-use of the proposed technique in purifying (or concentrating) a droplet in DMF. The results show that using the proposed nDEP electrode geometry purification (or concentration) can be performed with the efficiency of 90 %.     

Composite silver electrode for double‐sided‐emitting stacked organic light‐emitting diode

Abstract— A reflective composite silver electrode is proposed and characterized as the middle electrode of a stacked organic light‐emitting diode (OLED) with double‐sided light emission. The proposed electrode is composed of a thermally evaporated stack of LiF (1 nm)/Al (3 nm)/Ag (70 nm) layers. The LiF/Al and the plasma‐treated Ag of the electrode function well as the respective cathode and anode of the bottom‐ and top‐emitting stacked OLEDs, with both being of the non‐inverted type. Power efficiencies of 10.3 and 12.1 lm/W at 100 cd/m² have been measured for bottom‐ and top‐emitting OLEDs, respectively, using dye doping. The stacked OLED having this bipolar middle electrode can be constructed as a two‐terminal‐only device, allowing for simpler driving schemes in double‐side‐emitting passive‐/active‐matrix OLED displays.     

Effect of doping ferrocene in the working fluid of electrohydrodynamic (EHD) micropumps

The effect of doping ferrocene in the working fluid of electrohydrodynamic micropumps was investigated under the application of DC electric fields. The micropump consisted of 100 planar electrode pairs that were embedded along the bottom wall of a 100-micron-high, 5-mm-wide and 26-mm-long microchannel. The width of the emitter and collector electrodes was 20 and 40 µm, respectively, with inter-electrode spacing of 30 µm. A redox dopant, ferrocene, was diffused homogeneously into the working fluid HFE-7100 at 0.05, 0.1 and 0.2 % concentration by weight. The static pressure head generation and flow rate at different back pressure conditions were measured under different applied DC voltages. The current and pressure generated with the doped working fluid were significantly higher than with pure HFE-7100 under an applied DC field. A maximum static pressure of 6.7 kPa and flow rate of 0.47 mL/min at no back pressure were achieved at 700 V.     

A novel approach for estimating heat transfer coefficients of ethylene glycol–water mixtures

Ethylene glycol–water mixtures (EGWM) are vital for cooling engines in automotive industry. Scarce information is available in the literature for estimating the heat transfer coefficients (HTC) of EGWM using knowledge-based estimation techniques such as adaptive neuro-fuzzy inference systems (ANFIS) and artificial neural networks (ANN) which offer nonlinear input–output mapping. In this paper, the supervised learning methods of ANFIS and ANN are exploited for estimating the experimentally determined HTC. This original research fulfills the preceding modeling efforts on thermal properties of EGWM and HTC applications in the literature. An experimental test setup is designed to compute HTC of mixture over a small circular aluminum heater surface, 9.5 mm in diameter, placed at the bottom 40-mm-wide wall of a rectangular channel 3 mm × 40 mm in cross section. Measurement data are utilized as the train and test data sets of the estimation process. Prediction results have shown that ANFIS provide more accurate and reliable approximations compared to ANN. ANFIS present correlation factor of 98.81 %, whereas ANN estimate 87.83 % accuracy for test samples.     

A novel MEMS elastic-based dry electrode for electroencephalography measurement

Electroencephalogram (EEG) has been one of the important means to study brain functions and diseases. We fabricated an innovative MEMS elastic-based dry electrode using photolithography and electroforming process. The pitch of elastic-based dry electrode tip is 100 μm. We adopted polydimethylsiloxane as an elastic layer which provides the flexibility when the conductive layer and the electrode tip contact with the skin. This kind of dry electrode array does not need conductive gel during testing procedure. Compared with the traditional Ag/AgCl wet electrode, it greatly reduced the preparation time for EEG measurement and it could make the examinee more comfortable.     

Li2CO3-YSZ-SrCO3敏感电极的CO2电化学传感器研究

借助X射线衍射(XRD),扫描电镜(SEM)分析方法,研究以Li2CO3-YSZ-SrCO3作为敏感电极的氧化锆(YSZ)固体电解质CO2传感器.结果表明,在实验条件(450℃,CO2浓度(34 100 ～ 576 800)×10-6)下,传感器对CO2浓度变化具有准确、快速的响应.Li2CO3-YSZ-SrCO3电极烧制温度对其性能有影响.750℃烧制时,ZrO2与Li2CO3和SrCO3反应较充分;725℃烧制时,反应较浅.比较而言,725℃烧制的传感器响应较好.     

A portable sample concentrator on paper-based microfluidic devices

Microfluidic paper-based analytical devices (µPADs) provide a promising solution for low-cost point-of-care diagnostic applications. However, much work remains to be done in optimizing their design and performance. Accordingly, this study investigates the preconcentration performance of µPADs comprising one, two and three convergent channels, respectively. The performance of the three devices is evaluated experimentally using fluorescein and a fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) sample with an initial concentration of 10^?5 M. It is shown that the single-channel µPAD achieves a 20-fold improvement in the sample concentration in approximately 2 min. By contrast, the double- and triple-channel µPADs achieve preconcentration factors of 60- and 140-fold, respectively. Finally, a portable concentrator device is proposed. The experimental results show that a 100-fold improvement in the FITC-BSA sample concentration can be obtained in approximately 110 s given the use of four 16-V batteries, yielding a practical point-of-care diagnostic device.     

Performance evaluation of copper ion selective electrode based on cyanocopolymers

A copper(II) ion selective electrode based on copper(II) salicylaniline Schiff's base complex in styrene-co-acrylonitrile copolymer (SAN) has been developed. The SAN-based membrane electrode containing copper(II)–Schiff's base complex, dioctylphthalate as plasticizer and sodium tetraphenylborate as an anion excluder exhibited a linear response with a Nerstian slope of 30 mV decade⁻¹ within the concentration range of 10⁻⁶–10⁻² mol dm⁻³ of Cu²⁺ ions. The prepared electrode has an average response time of 15 s to achieve 95% steady potential for Cu²⁺ concentration ranging from 10⁻⁴ to 10⁻² mol dm⁻³. The electrode has shown a detection limit of 10⁻⁷ mol dm⁻³ of Cu²⁺ ion with an average lifetime of 6 months. The selectivity of electrode for Cu²⁺ ion has been found to be better in comparison to other various interfering ions. The electrode is suitable for use within the pH range of 2.0–7.0 at 1.0×10⁻³ mol dm⁻³ of Cu²⁺ ion. The prepared electrode can be used successfully as an indicator electrode for the potentiometric titration of the Cu²⁺ ion using EDTA.     

Sheathless microfluidic particle focusing technique using slanted microstructure array

This paper proposes a microfluidic channel for particle focusing that uses a microstructure on the bottom of the channel. Particles can be effectively focused in channels with bottom structures because of microvortex induced by the structure. Microchannels with top structures (top type) and bottom structures (bottom type) were fabricated. The focusing ratios in the focusing region (one-eighth of the channel width) were 86 % in top type and 89 % in bottom type at a flow rate of 1 μl/min. When the flow rate was increased to 5 μl/min, particles in top type were barely focused, whereas particles in bottom type were focused with a focusing ratio of approximately 80 %. We also evaluated the effect of a slanted angle for the microstructures. The comparative experiment was conducted with microstructures fabricated at slanted angle intervals of 20° (20°, 40°, 60°, and 80°) and 10°. The results indicated that the slanted angle (20°) required a small number of microstructures to direct the sample to the focusing region. For microstructures with a 20° slanted angle, the sample was focused after passing through 20 microstructures (10 mm). However, microstructures with an angle of 80° needed over 70 microstructures (over 23 mm) to direct the particle. In this sense, a microchannel with microstructures slanted at 20° is applicable to miniaturized devices. These results show that the microchannel with bottom structures slanted 20° can be used to effectively focus samples with advantages of applying various ranges of flow rates and miniaturizing devices.     

Pt/Ni—氧化石墨烯修饰电极用于莱克多巴胺测定

将石墨烯作为基底材料修饰到玻碳电极上,并在其表面沉积Pt/Ni二元金属制得定量检测莱克多巴胺的电化学传感器。探讨了石墨烯表面金属合金沉积时间和样品富集时间等条件对传感器性能的影响。在最优条件下,测定莱克多巴胺的浓度线性范围为1.98×10-7～2.67×10-4mol/L,其检测限为6.66×10-8mol/L。实验结果表明:该传感器灵敏度高、稳定性好。     

Simulation and characterization of dynamic contact in a MEMS passive vibration threshold sensor

A micro-machined passive vibration threshold sensor with a compliant stationary electrode has been designed, simulated and characterized. Bridge-type elastic beams as the compliant stationary electrode is adopted to improve the contact effect of the vibration threshold sensor and prolong its contact time. The dynamic contact between the two electrodes of the micro-machined vibration threshold sensor is simulated and analyzed by finite-element method (FEM). It’s indicated that a ‘skip contact’ phenomenon occurred during the switching on, which has been described and successfully explained in this paper. Deformations and stress distributions of the compliant electrode during contact under 55 g half-sine applied shock acceleration is also simulated. An all-metal cap that can undergo 6.08 × 10⁵ Pa has been designed and fabricated by UV-LIGA process for package of the vibration threshold sensor. A drop hammer test of the fabricated vibration threshold sensor has been done, which is in accordance with the FEM simulation of dynamic contact process. The measured response time of the threshold sensor is about 0.3 ms under 55 g applied acceleration and two contact times in the skip contact are 16 and 4 µs, respectively, which are in agreement with simulated results. The obtained natural frequency of the vibration threshold sensor by a vibration test is about 810 Hz in the first model, which also agrees with the model.