Microfluidics and Nanofluidics最新文献

We present a multiscale method for simulating non-equilibrium lubrication flows. The effect of low pressure or tiny lubricating geometries that gives rise to rarefied gas effects means that standard Navier–Stokes solutions are invalid, while the large lateral size of the systems that need to be investigated is computationally prohibitive for Boltzmann solutions, such as the direct simulation Monte Carlo method (DSMC). The multiscale method we propose is applicable to time-varying, low-speed, rarefied gas flows in quasi-3D geometries that are now becoming important in various applications, such as next-generation microprocessor chip manufacturing, aerospace, sealing technologies and MEMS devices. Our multiscale simulation method provides accurate solutions, with errors of less than 1% compared to the DSMC benchmark results when all modeling conditions are met. It also shows computational gains over DSMC that increase when the lateral size of the systems increases, reaching 2–3 orders of magnitude even for relatively small systems, making it an effective tool for simulation-based design.

Blood plasma is used in more than 90% of blood diagnosis tests, microfluidics devices for separating plasma from whole blood can be utilised to multiple clinical laboratory and point-of-care diagnostics. To separate blood plasma, this research developed a structural design for microfluidic channels. The blood flow behaviour in microchannels has been modelled using the Euler–Euler Laminar Flow Model in COMSOL Multiphysics™. Differently designed microchips with segregating microchannels were created and subjected to investigation. Investigations were done on the geometrical impact of microchannels on plasma separation. Simulation results show that channel model contributes little in displacement or isolating the cells in low flow rate and become a difficult model in the case of blood separation, because it involves capturing the intricate fluid–particle interactions, such as hydrodynamic forces, particle–wall interactions, and particle–particle interactions. Studies on the angle between the main channel and side channels in trifurcation as well as bifurcation, different separator shapes, such as triangular, square, and serpentine, with a focus on the serpentine separator width with outlet bifurcation, show that there is a sudden change in flow direction of the cell free layer to obtain more plasma with a higher purity. By altering the angle of the outlet bifurcation and linearly increasing the diameter of the serpentine, an optimum design with many channels has been presented and evaluated.

Early detection of pulmonary responses to silica aerosol exposure, such as lung inflammation as well as early identification of silicosis initiation, is of great importance in disease prevention of workers. In this study, to early screen the health condition of the workers who are exposed to respirable silica dusts, an immunoassay lab on a chip (LOC) was designed, developed and fully characterized for analyzing Clara cell protein 16 (CC16) in serum which has been considered as one of the potential biomarkers of lung inflammation or lung damage due to the respirable silica dusts. Sandwich immunoassay of CC16 was performed on the LOC developed with a custom-designed portable analyzer using artificial serums spiked with CC16 protein first and then human serums obtained from the coal mine workers exposed to the respirable silica-containing dusts. The dynamic range of CC16 assay performed on the LOC was in a range of 0.625–20 ng/mL, and the achieved limit of detection (LOD) was around 0.35 ng/mL. The assay results of CC16 achieved from both the developed LOC and the conventional 96 well plate showed a reasonable corelation. The correlation between the conventional reader and the developed portable analyzer was found to be reasonable, resulting in R² ~ 0.93. This study shows that the LOC developed for the early detection of CC16 can be potentially applied for the development of a field-deployable point-of-care testing (POCT) for the early monitoring of the field workers who are exposed to silica aerosol.

In the context of the COVID-19 epidemic, enhancing the transport of analyte to a sensor surface is crucial for rapid detection of biomolecules, since common conditions including low diffusion coefficients cause inordinately long detection times. SAW-based method owns low propagation loss, low power consumption, and ease of integration. However, the microstreaming effect is not stable and predictable using the bubble-induced acoustofluidic mixers. There is a strong need for developing efficient and robust acoustic devices for enhancing immunoassays. We herein take advantage of dual SAW streaming flow to enhance a continuous and non-invasive mixing of the target molecule with the immobilized antibody region. Acoustic streaming flow is utilized to stir the flow field in the micro-chamber, accelerate the transport of analyte to the functionalized surface and simultaneously minimize the localized target depletion. Using simulations, an optimized design of the proposed microfluidic chip is proposed based on the immunoassay enhancement by investigating the influences of the position of the reaction surface, the chamber height, the excitation frequency, the applied voltage, the antibody concentration, and the reaction rate on the binding performance. To the best of authors’ knowledge, it is the first investigation of enhancing immunoassays in SAW-based devices by optimizing the key parameters using simulations. As a result, the sensor target interaction can be enhanced and the nonspecific molecules can be simultaneously displaced from the reaction surface. The current Acoustic streaming flow assisted immunoassay technology can also be extended to other proteins, DNA and cell analysis.

Small, single-layer microfluidic paper-based analytical devices (µPADs) offer potential for a range of point-of-care applications; however, they have been limited to low flow rates. Here, we investigate the role of laser cutting paper channels in maximizing flow rate in small profile devices with limited fluid volumes. We demonstrate that branching, laser-cut grooves can provide a 59.23–73.98% improvement in flow rate over a single cut, and a 435% increase over paper alone. These design considerations can be applied to more complex microfluidic devices with the aim of increasing the flow rate, and could be used in stand-alone channels for self-pumping.

An experimental visualization is undertaken to investigate the impact dynamic behaviors of water, absolute ethanol, and low surface energy droplets with different viscosities impacting on hydrophobic surfaces. Droplets’ impacting behaviors, including spreading, rebounding, and oscillation retraction, are observed and quantitatively characterized by transient spreading factor and maximum spreading diameter. Effects of droplet impact velocity, surface wettability, and droplet viscosity on the impact dynamics are explored and analyzed. As the droplet impact velocity increases, the droplet kinetic energy increases, resulting in an increase in the spreading factor and spreading velocity simultaneously. Hydrophobic surfaces are not easy to be wetted by water droplets due to their low surface energy, leading to the partial rebound of water droplets when impacting on the hydrophobic surfaces. However, this phenomenon does not occur when low surface energy droplets, such as absolute ethanol and simethicone, impact on hydrophobic surfaces at the same velocity. The increasing droplet viscosity enhances the viscous dissipation, slowing down the impact process and inhibiting the droplet spreading, oscillation, and retraction behaviors. Based on the energy conservation method, a universal model for the maximum spreading factor of low surface energy droplets with different viscosities impacting on hydrophobic surface was established. According to the experimental results, a new spreading time model t_m = 2D₀/U₀ was proposed to enhance applicability of the model for low surface energy droplets with high viscosity, reducing the calculation error to less than 10%.

Miniaturization of biological and chemical analytical devices with microelectromechanical systems (MEMS) technology is important for medical diagnosis, microbial recognition, and other biological analysis. Current or emerging infectious diseases increase the need for point-of-care testing (POCT) to increase timely diagnosis and treatment. Among the various nucleic acid amplification methods, polymerase chain reaction (PCR) has been the most used method due to its simplicity. MEMS and microfluidic technologies enable PCR processes to be miniaturized in a chip. A miniaturized microfluidic chip is a small device that can limit and flow a specific volume of fluid into micro-sized channels. Microfluidic chip has potential benefits such as speed, cost, portability, efficiency, and automation. In addition to these benefits, multifunctional POCT PCR devices based on microfluidics technology can help with clinical diagnosis in underdeveloped nations that need a centralized health care system. In this review, conventional PCR method and the recent advances in microfluidic PCR amplification technologies, including its usage for POCT, are discussed. Current studies in commercialization of microfluidic PCR devices are presented. POCT has become very important during the Coronavirus disease (COVID-19) epidemic; therefore, the applications that evolved with combined use of POCT, PCR, and microfluidics during the COVID-19 pandemic were also covered.

Despite the fact that there are not a few relative studies, the effects of geometrical confinement on droplets’ generation at micro-T-junctions are not explicitly addressed. A three-dimensional volume of fluid (VOF) CFD model is developed here to study this classic microfluidics problem. The micro-T-junctions are designed with arms of a same hydraulic diameter but different width-to-depth ratios ((chi ) = 1/10–10), covering both deep-style ((chi <1)) and flat-style T-junctions ((chi >1)). It is found that the width-to-depth ratio (confinement style) shows complex effects on the dynamics of droplets’ generation. At (chi le 1/10), droplets are failed to be generated at the T-junctions. Compared to the normal T-junctions ((chi >1)), the deep-style T-junctions ((1/6<chi <) 1) show much higher generation frequency of droplets at ({mathrm{Ca}}_{mathrm{c}}>0.06) and the volume of generated droplets scales with ({{mathrm{Ca}}_{mathrm{c}}}^{-1}) instead of typical ({{mathrm{Ca}}_{mathrm{c}}}^{-0.33}). The comparative study of two paired T-junctions with reciprocal width-to-depth ratio (e.g., a deep-style T-junction, (chi ) = 1/3 and a flat-style T-junction, (chi ) = 3) explicitly illustrates that the geometrical confinement stabilizes the generation dynamics of droplets at T-junctions. The mechanism for the stabilization effect is discussed. It provides some new insights in terms of designing devices of droplets’ generation.

In this study, the separation of micron-size particles from a liquid slug is achieved by using a passive mechanism through Taylor’s flow. We have exploited the recirculation of a fluid along the travelling air–liquid interfaces to align particles in a streamline. Recirculation of concentrated particles is achieved along the centre of the microchannel that aligns with the maximum velocity plane across the channel. The microchannel is fabricated through a four-step manufacturing process to achieve the necessary dimensions and surface chemistry along the side wall of the microchannel. For a flow of liquid, a fully developed flow regime can be witnessed by observing the parabolic velocity profile. The symmetric profile with maximum velocity along the center line of the channel is a depiction of the no-slip boundary at the channel wall. A liquid-repellent solid wall, or a superhydrophobic solid wall, changes the parabolic profile and subsequently, the magnitude and position of maximum velocity changes. Along a channel with one wall of superhydrophobic coating, the profile becomes asymmetric and the shifts location of the maximum velocity from the center of the channel. After introducing a bubble of the same size as the channel width, the bubble also experiences this asymmetry. As famously Taylor flow depicts, the traveling bubble concentrates the particles along a maximum velocity profile which is along the center of the channel towards the wall with slp condition. However, for one wall with slip condition, it facilitates the shift of the stream of particles on the desired side of the center of the channel. This shift is used to guide particles towards one arm of the Y section of the channel located downstream of the flow. To demonstrate this shift in the particle stream, we conducted experiments along two different channels: one with no slip condition, and the second with a coating that exhibits slip condition along the wall.

It is a well-established fact that legally sound evidences are required to prove or disprove any criminal activity. When a particular activity occurs, it leaves a trace out of mutual contact and failure to detect that trace proves the activity did not occur. To enhance the capabilities of the justice system in evaluating evidence, researchers are continuously engaged in the development of novel analytical techniques which provide scientific methodologies for effectively assessing and interpreting the evidence associated with criminal activities. Among the several devices available, paper-based microanalytical devices (μPADs) have attracted the interest of forensic scientists/experts in recent years. These devices are designed with microchannels to which dedicated reagents are added for promoting selective reactions. As a result, they offer a practical and convenient solution for on-site detection of physical evidence, providing ready-to-use capabilities for forensic investigations. This does not only help the investigators in collection of legally sound evidences but also open avenues in apprehending the potential offender who might be present in the scene by detecting the traces. μPADs are inexpensive, simpler to operate, require less chemical consumption, portable, and provides results visible to naked eye. Furthermore, with the aid of digital scoring of color intensity, semi-quantitative results can be generated. This review explains current state of applications and operating chemistry of µPADs involved in analysis of evidences of forensic interest such as explosives, gunshot residue, drugs of abuse, pesticides, body fluids, and estimation of time since death. Furthermore, the research gaps in the domain and viability of future trends for the application of µPADs in forensic science are also presented.