Microfluidics and Nanofluidics最新文献

The acoustic radiation force (ARF) acting on particles measures the performance of microfluidic devices driven by standing surface acoustic waves (SSAWs). However, existing ARF calibration techniques rely on image post-processing or additional equipment. This work proposes a look-up table method to determine the ARF by examining the particle acoustophoresis mode in discrete phase-modulated SSAW fields, where the phase difference between the two counter-propagating SAWs is changed at fixed time intervals. Theoretical analysis indicates that particles in a straight channel migrate laterally either in the “locked” mode or the “drift” mode, while mode switching can be observed when the interval reaches a critical value highly dependent on the ARF amplitude. A look-up table can then be established for a given SSAW device. By observing the particle acoustophoresis modes at different phase-changing intervals, the ARF amplitude can be obtained from the easily determined critical interval. The procedure is demonstrated experimentally in an SSAW acoustofluidic device and compared with the particle tracking protocol to verify the former’s effectiveness and demonstrate its operational simplicity. Inspired by the established theory, a method to improve the efficiency of particle acoustophoresis by optimizing the phase-modulating parameters is also proposed.

The reliable conjugation of antibodies to a solid matrix is crucial for robust immunoassays in microfluidic devices. Various magnetic particles (MPs) have been employed due to their high surface-to-volume ratios and ease of magnetic manipulation, providing a reliable surface for antibody immobilization. However, achieving uniform positioning of MPs across the channel surface has been challenging due to inadequate magnetic forces or magnetic field uniformity. Here, we present the utilization of Halbach magnetic arrays to enable consistent deployment of MPs on the microfluidic surface, thereby facilitating robust immunoassay capabilities. Using finite element method magnetics (FEMM) simulations, we predicted that incorporating Halbach magnetic arrays beneath the microfluidic channels would create more uniform and augmented magnetic flux density gradients over the surface. Subsequently, we applied this platform to assess cancer biomarkers in patients’ blood plasma and achieved statistically reliable results, comparable to those obtained using an FDA-approved device. We detected three cancer biomarkers, including prostate-specific antigen (PSA), alpha-fetoprotein (AFP), and carcinoembryonic antigen (CEA). The limit of detection (LOD) of three biomarkers were < 1 ng/mL, ranging from 0.38–0.95 ng mL⁻¹. This platform provided within-run, between-run, and between-day precisions for the three cancer biomarkers, ranging from 0.37–9.87%. This advancement holds significant promise for improving the accuracy and performance of immunoassays in various microfluidic diagnostic applications.

Mobility manipulation of liquid droplets is an important task of digital imicrofluidics. Acoustic levitation has revolutionised the contactless manipulation of liquid droplets for various applications. Acoustic levitation technique can be effectively used to manipulate droplets to obtain their coalescence. This paper reports a unique, versatile, and material-independent approach for the vertical coalescence of the droplets suspended in an acoustic levitator. The acoustic power of the levitator is carefully engineered to obtain vertical coalescence of two liquid droplets. Water, 20% and 40% glycerol–water solutions are used as the working liquids. The results of the experiments revealed three outcomes during the coalescence. The outcomes are analysed and discussed.

Numerical investigations of high-speed rarefied gas outflow into a vacuum through channels with a forward- or backward-facing step have been conducted using the direct simulation Monte Carlo method. Calculations have been performed for various free-stream Mach numbers, covering transonic, supersonic, and hypersonic flow regimes, and over a wide range of gas rarefaction from free molecular to near hydrodynamic conditions. Mass flow rates through the channel and the gas flow field have been accurately calculated both inside the channel and in the regions upstream and downstream. It has been established that channel geometry, the free-stream velocity, and gas rarefaction strongly influence the gas flow. In the flow field, in front of the channel, a phenomenon known as a detached shock occurs, while inside the channel, a gas recirculation zone may form.

Microfluidic flow control systems are critical components for on-chip biomedical applications. This study introduces a new micropump for on-chip sample preparation and analysis by using an acoustic nozzle diffuser mechanism. The micropump implements a commercially available transducer and control board kit with 3D-printed fluid reservoirs. In this micropump, conic-shaped micro-holes on the metal sheet cover of the transducer are employed as oscillating nozzle diffuser micro arrays to achieve directional flow control. The micropump is shown to efficiently pump water and particle mixtures exceeding flow rates of 515 µl/min at a 12-volt input voltage. In addition, owing to the small size of the nozzle hole opening, larger particles can also be filtered out from a sample solution during fluid pumping enabling a new function. Importantly, the micropump can be fabricated and assembled without needing a cleanroom, making it more accessible. This feature is advantageous for researchers and practitioners, eliminating a significant barrier to entry. By combining commercially available components with 3D printing technology, this micropump presents a cost-effective and versatile solution for on-chip applications in biomedical research and analysis.

A method is proposed to deterministically obtain steady lubrication pressure for the Stokes flow in a channel bounded by a flat wall and a surface with roughness represented by sinusoidal waves. A streamline sufficiently far away from the rough surface is used to formulate a streamline-based lubrication equation with the velocity on the streamline, and the velocities on the streamline is imposed as a boundary condition. In the solution of the lubrication equation, by virtually moving the streamline towards the flat wall, the pressure on the flat wall is obtained, and then the wall-normal variation of the pressure is recovered from the wall pressure by a lubrication model that considers higher order terms. The proposed method is applied to lubrication flows in channels with roughness represented by a single sinusoidal wave and a superposition of several sinusoidal waves. Through comparison with analytical solutions, the validity of the proposed method is established, and the applicable range of superposition of waves is explained that lowest-wavenumber component in surface profile is sufficiently isolated from higher-wavenumber components. Although the problem setting intrinsically prohibits the application of the conventional Reynolds lubrication equation, this study provides new understandings for the pressure obeying the Reynolds lubrication equation and the role of the higher-order terms.

This study introduces an innovative method aimed at achieving exceptional stability in emulsions. The primary focus is on re-emulsifying precisely controlled and uniform initial single emulsions, generated by microfluidic devices, to produce single-core double emulsions and core–shell microparticles. Departing from traditional approaches, our method employs a unique combination of advanced Two-level fractional factorial design and numerical simulation. These tools are utilized to discern and optimize critical parameters necessary for the formation of highly monodispersed stable single emulsions and their subsequent transformation into double emulsions. Correlations are established to estimate the size and stability of the primary single emulsion based on immiscible phase flow rate ratio and surfactant concentration. These correlations provide a comprehensive understanding that facilitates the intentional development of desired water-in-oil emulsions. The proposed microfluidic paradigm shows promise for the controlled and efficient production of single-core double emulsions, with broad applications in Pharmaceuticals, Food, and Cosmetics.

We present the control of liquid flow through arrayed micron-sized pores in a macroporous silicon membrane. The pores are coated with about 150 nm polymer N-isopropylacrylamide (pNIPAAm) hydrogel brushes and 200 nm polypyrrole layer, which works as photothermal actuator. The size of pore openings is controlled by utilizing the swelling and de-swelling behavior of temperature-sensitive pNIPAAm brushes, and the temperature on pNIPAAm brushes is changed by 815 nm near infra-red (NIR) illumination to polypyrrole photothermal element layer. The dimension change of the pore openings is investigated by observing the transmitted light and fluorescence signal intensity through the pores in the membrane while changing the ambient temperature. It has shown that the intensity of transmitted light can be controlled by adjusting the ambient temperature across the low critical solution temperature (LCST) of the hydrogel brushes. The localized control of liquid flow through the pores is demonstrated by the diffusion of fluorescein dye from the bottom of the membrane to the surface of the membrane using pulsed NIR light illumination. Fast dynamic response of fluorescein dye diffusion upon the illumination of NIR light suggests that the presented photothermal actuation approach could be applied to diverse biomedical applications such as a localized drug release system.

Some anticancer treatments may cause Multidrug Resistance (MDR). In these cases, cells pump the drug out of the intracellular environment, thereby preventing drug effects. Several strategies have been used to avoid MDR, including using two or more drugs at low concentrations to increase the sensitivity of cells to treatment. We present an effective, cheap, fast microfluidic alternative to test two drugs simultaneously using a reversible sealing and reusable device to determine the optimal concentration. We used the rugs doxorubicin (DOX) and paclitaxel (PXT) as proof of concept. The microdevice allows the testing of two drugs in real time. Furthermore, running two experiments in sextuplicates and control in the same microchip is possible. We used two combinations of drugs, varying the drug concentration (C₁ = 0.010 mg.mL^− 1 DOX and 0.002.mL^− 1 mg PXT, C₂ = 0.010 mg.mL^− 1 DOX and 0.004 mg.mL^− 1 PXT), and evaluated cell death over time. The intermediate drug concentrations were more efficient, reducing the time required to decrease the viability of breast tumor cells, MCF-7 (C₁ = 180 and C₂ = 120). In further analysis, the microdevice also allowed characterization of the effects of the drugs (antagonist, synergic, or additive). This microdevice is a reliable tool for estimating the different combinations of two drug concentrations in a single assay simply and quickly.