On hybrid electroosmotic kinetics for field-effect-reconfigurable nanoparticle trapping in a four-terminal spiral microelectrode array

Quantitative viability detection for a single microalgae cell by two-level photoexcitation

A novel method for quantitative detection of the viability of a single microalgae cell by two-level photoexcitation is proposed in this paper. This method overcomes the difficulty of traditional methods in determining the cell viability by a fixed standard under a single photoexcitation. It is experimentally confirmed that this method is not limited by the species, morphology, size and structure of microalgae cells. An evaluation criterion of universal applicability is presented for the assessment of cell viability based on the large amount of experimental data. To the best of our knowledge, this is the first time that the relative fluorescence yield ratio F_r has been used to characterize the viability of single microalgae cells during cell migration. By using the relative fluorescence yield ratio, this method does not require the intensity of the excitation light to be very low for the assessment of the fluorescence yield of a dark-adapted microalgae cell, nor to be very strong to reach the saturated light level to assess the maximum fluorescence yield. Therefore, this method greatly reduces the technical difficulties of developing a sensor device. Well balanced portability, accuracy and universal applicability make it suitable for on-site real-time detection.

Passivated-electrode insulator-based dielectrophoretic separation of heterogeneous cell mixtures

Rapid and accurate purification of various heterogeneous mixtures is a critical step for a multitude of molecular, chemical, and biological applications. Dielectrophoresis has shown to be a promising technique for particle separation due to its exploitation of the intrinsic electrical properties, simple fabrication, and low cost. Here, we present a geometrically novel dielectrophoretic channel design which utilizes an array of localized electric fields to separate a variety of unique particle mixtures into distinct populations. This label-free device incorporates multiple winding rows with several nonuniform structures on to sidewalls to produce high electric field gradients, enabling high locally generated dielectrophoretic forces. A balance between dielectrophoretic forces and Stokes' drag is used to effectively isolate each particle population. Mixtures of polystyrene beads (500 nm and 2 μm), breast cancer cells spiked in whole blood, and for the first time, neuron and satellite glial cells were used to study the separation capabilities of the design. We found that our device was able to rapidly separate unique particle populations with over 90% separation yields for each investigated mixture. The unique architecture of the device uses passivated-electrode insulator-based dielectrophoresis in an innovative microfluidic device to separate a variety of heterogeneous mixture without particle saturation in the channel.

Study on non-bioparticles and Staphylococcus aureus by dielectrophoresis

This article demonstrated a chip device with alternating current (AC) dielectrophoresis (DEP) for separation of non-biological micro-particle and bacteria mixtures. The DEP separation was achieved by a pair of metal electrodes with the shape of radal-interdigital to generate a localized non-uniform AC electric field. The electric field and DEP force were firstly investigated by finite element methods (FEM). The mixed microparticles such as different scaled polystyrene (PS) beads, PS beads with inorganic micro-particles (e.g., ZnO and silica beads) and non-bioparticles with bacterial Staphylococcus aureus (S. aureus) were successfully separated at DEP-on-a-chip by an AC electric field of 20 kHz, 10 kHz and 1 MHz, respectively. The results indicated that DEP trapping can be considered as a potential candidate method for investigating the separation of biological mixtures, and may well prove to have a great impact on in situ monitoring of environmental and/or biological samples by DEP-on-a-chip.

This article demonstrated a chip device with alternating current (AC) dielectrophoresis (DEP) for separation of non-biological micro-particle and bacteria mixtures.

A New Self-Activated Micropumping Mechanism Capable of Continuous-Flow and Real-Time PCR Amplification Inside 3D Spiral Microreactor

A self-activated micropump which is capable of stable velocity transport for a liquid to flow a given distance inside a 3D microchannel has been a dream of microfluidic scientists for a long time. A new self-activated pumping mechanism has been proposed in this paper. It is different from the authors’ previous research which relied on the fluid resistance of a quartz capillary tube or end-blocked gas-permeable silicone or a polydimethylsiloxane (PDMS) wall to automate the flow. In this research, an end-open stretched Teflon tube was utilized for passive transport for the first time. A new fluid transmission mode was adopted with the assistance of a cheaper easily accessible oil mixture to achieve stable continuous flow. Finally, this novel micropump has been applied to real-time continuous-flow polymerase chain reactions (PCRs), with an amplification efficiency similar to that of a commercial PCR cycler instrument.

Highly Sensitive Micropatterned Interdigitated Electrodes for Enhancing the Concentration Effect Based on Dielectrophoresis

The concentration effect of dielectrophoresis (DEP) enables detection of biomolecules with high sensitivity. In this study, microstructures were patterned between the interdigitated microelectrodes (IMEs) to increase the concentration effect of DEP. The microstructures increased the electric field gradient (∇|E2|) between the IMEs to approximately 6.61-fold higher than in the bare IMEs with a gap of 10 μm, resulting in a decreased optimal voltage to concentrate amyloid beta 42 (Aβ₄₂, from 0.8 V_pp to 0.5 V_pp) and tau-441 (from 0.9 V_pp to 0.6 V_pp) between the IMEs. Due to the concentration effect of DEP, the impedance change in the optimal condition was higher than the values in the reference condition at 2.64-fold in Aβ₄₂ detection and at 1.59-fold in tau-441 detection. This concentration effect of DEP was also verified by counting the number of gold (Au) particles which conjugated with the secondary antibody. Finally, an enhanced concentration effect in the patterned IMEs was verified by measuring the impedance change depending on the concentration of Aβ₄₂ and tau-441. Our results suggest that microstructures increase the concentration effect of DEP, leading to enhanced sensitivity of the IMEs.

Multifrequency Induced-Charge Electroosmosis

We present herein a unique concept of multifrequency induced-charge electroosmosis (MICEO) actuated directly on driving electrode arrays, for highly-efficient simultaneous transport and convective mixing of fluidic samples in microscale ducts. MICEO delicately combines transversal AC electroosmotic vortex flow, and axial traveling-wave electroosmotic pump motion under external dual-Fourier-mode AC electric fields. The synthetic flow field associated with MICEO is mathematically analyzed under thin layer limit, and the particle tracing experiment with a special powering technique validates the effectiveness of this physical phenomenon. Meanwhile, the simulation results with a full-scale 3D computation model demonstrate its robust dual-functionality in inducing fully-automated analyte transport and chaotic stirring in a straight fluidic channel embedding double-sided quarter-phase discrete electrode arrays. Our physical demonstration with multifrequency signal control on nonlinear electroosmosis provides invaluable references for innovative designs of multifunctional on-chip analytical platforms in modern microfluidic systems.

Simultaneous Pumping and Mixing of Biological Fluids in a Double-Array Electrothermal Microfluidic Device

Transport and mixing of minute amounts of biological fluids are significantly important in lab-on-a-chip devices. It has been shown that the electrothermal technique is a suitable candidate for applications involving high-conductivity biofluids, such as blood, saliva, and urine. Here, we introduce a double-array AC electrothermal (ACET) device consisting of two opposing microelectrode arrays, which can be used for simultaneous mixing and pumping. First, in a 2D simulation, an optimum electrode-pair configuration capable of achieving fast transverse mixing at a microfluidic channel cross-section is identified by comparing different electrode geometries. The results show that by adjusting the applied voltage pattern and position of the asymmetrical microelectrodes in the two arrays, due to the resultant circular flow streamlines, the time it takes for the analytes to be convected across the channel cross-section is reduced by 95% compared to a diffusion-only-based transport regime, and by 80% compared to a conventional two-layer ACET device. Using a 3D simulation, the fluid transport (pumping and mixing) capabilities of such an electrode pair placed at different angles longitudinally relative to the channel was studied. It was found that an asymmetrical electrode configuration placed at an angle in the range of 30°≤θ≤45° can significantly increase transversal mixing efficiency while generating strong longitudinal net flow. These findings are of interest for lab-on-a-chip applications, especially for biosensors and immunoassays, where mixing analyte solutions while simultaneously moving them through a microchannel can greatly enhance the sensing efficiency.

Microparticle separation using asymmetrical induced-charge electro-osmotic vortices on an arc-edge-based floating electrode

We developed a device for particle separation by designing an arc-edge-based floating electrode to alternately actuate opposite-direction asymmetrical induced-charge electro-osmotic vortices.