Microfluidics and Nanofluidics最新文献

Digital microfluidics (DMF) shows a great application prospect in droplet manipulation. However, the fouling of the hydrophobic surfaces caused by biomolecules limits its development. In this study, we report a new strategy to enhance the functionality and anti-biofouling performance of the DMF chip by using a hydrophobic liquid surface (HLS) rather than a regular hydrophobic solid surface (HSS). The DMF chip with such a configuration can efficiently drive various liquids with full-function operations. Moreover, our DMF chips can directly manipulate biomolecular droplets without restrictive conditions like adding surfactants or filling with silicon oil. The liquid-liquid contact between the droplet and the hydrophobic surface ensures that the non-specifically adsorbed biomolecules move along with the droplet. Thus, no residue is left behind to ruin the hydrophobicity of the hydrophobic surface. Meanwhile, the long-term reversibility of contact angle change and stability of droplet movement demonstrate the excellent ability against biofouling. In addition, high- and low-temperature tests also show the temperature stability of the HLS. Finally, a biochemical application, plasmid extraction of Escherichia coli (E.coli) cells, is successfully carried out on the DMF chip with HLS as a proof of its usability. This HLS is expected to offer versatile functionalities and anti-biofouling performance for DMF chips in handling biomolecular droplets.

The equilibrium properties and stability of droplets with arbitrary contact angles on atomically smooth solid surfaces are investigated using a mesoscopic model based on the Sutherland pair potential. New analytical expressions are derived for the equilibrium radius, potential energy, molar heat of evaporation, and work of adhesion of these droplets. Employing the Proximity Force Approximation (PFA), we calculate the internal pressure within the droplet arising from dispersion forces exerted by the substrate. Based on this pressure, we formulate an analog of the Young-Laplace equation applicable to nanoscopic droplets. Our analytical findings demonstrate that the rapid decay of dispersion forces invariably leads to a near-spherical shape of droplets on solid surfaces, a result that is consistent with existing experimental observations and molecular dynamics simulations. We reveal a geometric pseudo-phase transition in the adhesion work at a contact angle of (:simpi:/2), governed solely by the droplet shape. These results provide fundamental insights into the behavior of nanoscale liquid systems at interfaces.

The precise manipulation of biological nanovesicles such as exosomes is crucial for biomedical applications. However, their small size makes them difficult to handle with conventional viscoelastic microfluidics, as the key elastic forces diminish cubically with particle diameter. To overcome this challenge, we developed a novel hybrid microfluidic device featuring a 16-cm-long square channel for initial alignment, followed by a 4-cm-long cruciform channel for intensive final focusing. The unique geometry of the cruciform channel, with its four 270º reflex angles, generates strong, localized shear rate gradients. This effect dramatically amplifies the elastic forces responsible for migrating particles to the channel centerline. We demonstrated the device’s superior performance by focusing synthetic particles as small as 50 nm into a single, tight stream. Critically, we also achieved high-efficiency focusing and an approximately 29-fold enrichment of exosomes, which were subsequently collected at the central outlet with minimal diffusion. This robust, label-free platform represents a significant advancement in nanoparticle manipulation, holding great promise for high-throughput applications in diagnostics, nano-flow cytometry, and liquid biopsy.

Filtration is a crucial element in most industrial processes, which has led to the development of numerous commercially available membrane-based filtration techniques. Membranes are notorious for fouling requiring frequent replacement and high maintenance costs. Here, we re-evaluate membrane-less filtration techniques as a versatile alternate approach to suit different particle sizes and filtration purposes. Industrial sectors favor highly scalable processes, which can explain the rapid development in this research space. As an alternative to membrane filtration, microfluidic techniques are among the most innovative methods and benefit from low-cost fabrication technology, continuous operational mode, and clogging-free separation methods. This review highlights microfluidic technologies with the potential for scale-up that could pivot away from our use of expensive conventional filtration methods.

Despite the widespread adoption of green energy technologies, the improvement and development of new environmentally friendly and more energy-efficient methods of oil and gas production is still an urgent task. In this sense, the enhancement of surfactant–polymer flooding methods to increase oil recovery seems to be the most rational approach in terms of cost-effectiveness and equipment. This study systematically explores the possibility of increasing the efficiency of traditional surfactant solutions, polymers, and their composites through modification with nanoparticles using novel, unique microfluidic chips simulating terrigenous and fractured-cavernous reservoirs. Eight different oil-displacing fluids are investigated. AES-based surfactant solution and polyacrylamide solution are used as base solutions, to that effect modified with spherical silicon oxide nanoparticles with a size of 10 nm. The experiments serve to determine the dependences of the oil recovery factor and pressure losses during flooding of microchips with different pore space structures by the studied solutions. The experimental results have shown that introducing nanoparticles into solutions with surfactant–polymer compositions provides an additional significant increase in the oil recovery factor. The modification of the surfactant–polymer composition with nanoparticles increases the factor by 31.21%, compared to water, or by 19.23%, compared to the composition without the adding of particles. This opens up new prospects for improving the efficiency of traditional methods of oil recovery enhancement, i.e., surfactant–polymer flooding. The data obtained may serve as a basis for the development of new technologies aimed at improving oil recovery and optimizing oil production processes.

Inertial microfluidics is a passive particle manipulation technique, excelling in simplicity, precision, and high throughput. However, its restricted adaptability to varying particle sizes has limited its broader application. This study presents numerical simulations on a stretchable inertial microfluidic device that dynamically adjusts channel dimensions, enabling tunable particle focusing and separation. Building upon the experimental work by Fallahi et al. (Analytical Chemistry, 2020), we incorporate advanced numerical simulations to evaluate how channel stretching influences particle migration dynamics. We investigate the inertial focusing of 15 µm particles and the separation of 10-µm and 15-µm particles in a straight channel under varying stretching lengths. Stretching the channel length up to 6 mm resulted in a near-complete focusing efficiency of almost 100%. Furthermore, increasing the channel length enhanced the effective separation of 10- and 15-µm particles, achieving 100% separation efficiency and purity. We identify an optimal stretching length that maximizes the separation efficiency, thereby confirming the device’s effectiveness. Qualitative and quantitative validation demonstrate excellent agreement between experimental and simulation results, with an accuracy of 99.82% and an average error of 0.18%, underscoring the reliability of the proposed model. The simulated stretchable device, capable of dynamically adjusting the channel dimensions in real time, opens up new perspectives and potential applications with enhanced tunability and performance of inertial manipulation, focusing, and separation of particles.

Postoperative infections remain a critical concern in surgical care, particularly in resource-limited or field-based operating environments. Paper-based microfluidic diagnostics offer a practical solution for rapid, on-site pathogen detection to support sterile conditions and timely clinical decisions. This review outlines key developments in paper-based testing, from early use of cellulosic substrates and colorimetric assays to more recent integration with smartphone imaging and artificial intelligence (AI). We examine the progression from single-analytic tools to multiplexed systems capable of detecting bacteria, viruses, and biofilms. Highlighted examples include enzyme-linked immunoassays, biofilm-specific staining techniques, and IL-6–based inflammatory markers. We further discuss how convolutional neural networks (CNNs) enhance interpretive accuracy and enable semi-quantitative analysis via mobile platforms. We summarize recent advances in paper-based analytical devices for rapid on-site pathogen detection in resource-limited surgical environments, with a focus on sensitivity, operational simplicity, and readiness for field deployment. In addition, we highlight emerging multiplexing capabilities that enable simultaneous detection of multiple pathogens, representing an important direction for perioperative infection prevention.

With the increasing application of droplet microfluidics, more and more attention has been focused on the significance of precise droplet manipulation. However, the mechanism of the reverse electrowetting (REW)-driven droplet dynamic behavior is not well understood. In this work, the physical factors responsible for different movement behaviors of the droplet (~ 20 µL) under various alternating current (AC) frequencies are explored, and theoretical models are established to describe the droplet attachment/detachment. Meanwhile, simulations and experiments are carried out to validate the theoretical predictions. It shows that successful detachment of the droplet depends on the driving voltage, but more importantly on AC frequency. When the AC frequency is lower than 800 Hz, the droplet always adheres to the substrate no matter how high the driving voltage is. As the AC frequency varies in the range of 850 Hz ~ 950 Hz, the droplet motion enters into the uncertain state. In this state, the droplet attaches or escapes mainly depending on whether the transient contact angle is larger than the critical contact angle, i.e., the critical contact angle of the droplet is the dominant factor determining the droplet detachment or attachment. When the AC frequency increases above 1 kHz, the droplet detaches from the substrate once the driving voltage is sufficiently high.

The present study explores anisotropy driven regulation of viscous fingering in a lifting Hele Shaw cell, enabling deterministic square mesh formation. A multiport plate with 0.5 mm source holes coupled with circumferential grooves of 1.5 mm width was investigated under controlled lifting and airflow and interpreted using a Darcy Herschel–Bulkley framework. Under moderate lifting rates of 4 to 5 mm per minute and a high-viscosity resin of approximately 1.57 × 10⁶ cP, the initially stochastic interface transitions into reproducible 5 × 5 mm lattices, consistent with analytical predictions for a stable composite regime ((varLambda = {C}_{a}^{*}/{B}_{n}) ≈ 10⁻² to 10⁻¹). The measured finger-to-pitch ratio (w/p  ≈ 0.22 to 0.25) closely matches model estimates, confirming the predictive linkage between gap dynamics and pressure-field anisotropy created by groove–hole coupling. Experiments further reveal fractal-like kinetics with a confined fractal dimension of about 1.75 ± 0.05, while higher lifting velocities or reduced viscosities induce morphological disorder due to elevated (:{C}_{a}^{*}) and weakened tip shielding. Perfect mesh formation requires the combined effects of geometric anisotropy, which defines orthogonal pressure minima, and boundary-controlled air entry that homogenizes the pressure gradient. These findings establish a predictive, lithography-free framework for template-assisted microfluidic patterning and tuneable porous architectures guided by controlled interfacial anisotropy.

The fabrication process of the liquid-infused surface (LIS) usually involves complicated surface modifications or is substrate-limited. In this study, a new LIS coating on various material surfaces is reported, in which a highly porous polytetrafluoroethylene (p-PTFE) film is initially deposited and followed by the lubricant infusing into the nanostructures. The LIS-coated glass slides present improved transparency compared to bare ones and low contact angle hysteresis with different droplets. The capability of p-PTFE film in lubricant retention is demonstrated, and the durability test of the LIS is conducted. Small droplets (5 µL) can slide easily in a stereoscopic LIS-coated resin channel, exhibiting the adaptation of LIS in coating on complex topography surfaces. By applying a metallic shadow mask during the p-PTFE film deposition, the substrate’s surface is thus selectively modified, presenting various hydrophobic-hydrophilic patterns. Lastly, this LIS is applied in a digital microfluidics (DMF) chip on the Parylene-C and Indium Tin Oxide (ITO) surface. By patterning the chip’s surface, the precision of the droplets’ separation is significantly improved, and single polystyrene bead isolation is realized.

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