Microfluidics and Nanofluidics最新文献

Milk adulteration is a significant issue, particularly in regions where food safety regulations are weak or inadequately enforced. A cost-effective and straightforward paper-based lab-on-a-chip (LOC) microfluidic device has been developed using a technique known as selective wax impregnation. This technology is advantageous as it requires neither costly equipment nor specialised workers. It can detect prevalent milk adulterants such as urea, detergent, boric acid, soap, and hydrogen peroxide by a combination of chemiluminescent and colorimetric chemical reactions. This provides both visual and quantitative results. A crucial aspect of this technique is its utilisation of a smartphone to capture images, which are subsequently processed on-site using ImageJ software. This device effectively enhances food safety in resource-limited areas and facilitates community-level quality control without dependence on centralised laboratories. It is user-friendly, portable, and cost-effective to produce.

We present a new microfluidic method for the characterization of emulsion stability against coalescence within a microfluidic droplet-making device. In our device, the merging of droplets can be actively controlled under a wide range of flow conditions, using a simple structure. The new method combines features of already existing passive and active methods, hence we refer to it as a “hybrid” method. Our hybrid method allows for a relatively easy integration within any PDMS (polydimethysiloxane)-based microfluidic device comprising a droplet-making structure, since it employs a simple single-layer PDMS geometry. The main device structure comprises 2 pressure chambers, placed symmetrically along a locally expanded main channel, through which the droplets are flowing. By inducing an overpressure in the pressure chambers, a change of the cross-sectional area of the main channel is reached, which influences the droplets’ velocities and their mutual distance, and thus the coalescence rate. To test our hypotheses on the working principle of the device and to test its performance, we carry out systematic experiments at varying flow rates and applied pressures. These experiments confirm the hypothesized working principle of the device and indicate that the method is suitable for characterizing emulsion stability. Moreover, we show that the hybrid method is capable of actively controlling the creation of on-demand coalescence patterns and even of triggering specific single coalescence events. This indicates that the hybrid method, when integrated into a droplet-making device, can offer a promising approach both for characterizing the stability of emulsions and for controlling on-demand droplet coalescence.

Resistive Pulse Sensing has recently emerged as a promising technique for measuring and counting particles in electrolyte solutions, with applications in nanoparticle characterization, biomolecule analysis in micro-fluidic sensing. Resistive Pulse Sensing offers high single-particle sensitivity, real-time, and label-free detection. It can provide detailed information on particles including size and shape. Small pore diameters are required to detect small particles, but they limit the measurable range and carry the risk of clogging. This paper presents recent advancements in wafer-level Micro-Electro-Mechanical Systems technology specifically tailored for fabrication of microflow cells for Resistive Pulse Sensing. Key processes include femtosecond laser structuring, photolithography, etching, deposition, and bonding technologies which allow to enhance the scalability and reproducibility of the sensing platforms because they enable precise control of dimensional parameters that determine the sensitivity. To avoid clogging of very sensitive systems with very narrow pores, a bypass flow architecture was implemented that allows particles that are too large to pass through the pores to leave the sensor system. The bypass system also offers the advantage of operating without the need for sample filtration. The fabricated sensors are reusable, durable, and practical for diverse applications. Two types of micropores were fabricated, each 100 μm in length and square cross-sections with nominal edge lengths of 8 μm and 1 μm. The RPS measurement using both pores demonstrated the ability of the system to determine particle sizes with an uncertainty of +/- 10%. The Resistive Pulse Sensing measurement with the 1 μm pore proved to detect nanoparticles as small as 350 nm in diameter.

Controllable mass production of monodisperse droplets is crucial in various fields, ranging from scientific research to industrial applications, while microfluidic ladder networks have shown enormous potential in this regard. However, current design strategies often aim to mitigate the adverse effects of distribution channel resistance by increasing droplet generator resistance, which significantly elevates overall system pressure and reduces integration efficiency. In this paper, we introduce a design rule for ladder-type parallel microfluidic devices, referred to as the “gradually varying resistance rule.” In this approach, each droplet generator is designed with a distinct flow resistance, ensuring that the flow resistance between each droplet production unit and the fluid inlet is balanced. Single-phase flow simulations and droplet production experiments conducted on parallel devices with 50 droplet generators demonstrate that, compared to existing constant resistance rules, the gradually varying resistance rule not only ensures uniform fluid distribution but also improves device integration. Moreover, due to lower flow resistance, it allows for more efficient droplet production at the same driving pressure. The gradually varying resistance rule offers a rational framework for the efficient development of microfluidic ladder networks with uniformly distributed flow rates, facilitating the mass production of highly monodisperse droplets.

Stress is a disease of modern life generated by excess cortisol hormone levels. A paper-based microanalytical device (µPAD) was developed to analyze cortisol in human saliva samples without prior purification treatment. The design includes optimized flow channels to use freshly extracted human saliva samples. The density, viscosity, and pH properties of human saliva and artificial saliva models were characterized. These properties helped to establish optimal theoretical dimensions for our µPAD design, which works with untreated human saliva. A microfluidic engineering analysis was performed to understand the dynamics of the sample flow in the sensor, obtaining a design that allows free and rapid transport of freshly extracted human saliva, covering the surface of the µPADs in approximately three minutes. Its characteristic design allows for the direct use of human saliva without pretreatment, making it an effective tool as a universal device with multiple applications in different research fields, specifically as a point-of-care (POC) device. After the design was developed, a proof-of-concept method based on colorimetric detection of salivary cortisol, similar to enzyme-linked immunosorbent assay (ELISA) analysis, was performed using gold nanoparticles. The colorimetric response was obtained after 7 min of adding the fresh human saliva sample and the corresponding feedback after UV light lamp illumination. The authors designed a paper-based sensor that works with freshly extracted human saliva without any previous treatment for the detection of hormonal stress, generating an advance in biomolecular detection for use as a POC tool.

As the global energy demand grows, with oil consumption projected to reach 102.1 million barrels per day in 2024, maximizing oil extraction from known reserves has become critical. In this study, we demonstrate a preparation method for water-wet microfluidic chips and investigate two-phase flow repulsion experiments at the microscale. Four pore structures of porous media with different characteristics were designed based on the Voronoi surface subdivision algorithm, and water, surfactant, and polymer repulsion experiments were carried out at a repulsion rate of 0.2 µl/min. The results quantitatively demonstrate that increasing pore structure complexity reduces the final recovery rate, with the simplest Voronoi structure 1 achieving 81.7% recovery compared to 53.2% for the most complex Voronoi structure 4. The water injection channels overlap with the ‘dominant channels’ generated by the pore structure, with breakthrough times varying from 15.2 min for Voronoi 1 to 12.6 min for Voronoi 4. Areas with pore throats smaller than 60 μm show significantly reduced fluid penetration due to increased capillary resistance. The injection of surfactants improved recovery to 67.3% compared to 53.2% for water injection in Voronoi structure 4, primarily by reducing interfacial tension, while polymer injection achieved 62.1% recovery through improved sweep efficiency. Analysis reveals that the primary type of residual oil in these structures is ‘blind end residual oil’, formed due to the interplay of capillary forces and flow path development.

Paper-based microfluidic platforms are widely utilized in point-of-care (POC) diagnostics, filtration, and fluid handling due to their cost-effectiveness and simplicity. However, uncontrolled capillary-driven transport often results in performance inconsistencies, compromising sensitivity, specificity, and reproducibility. Hydrogel-infused paper matrices present a promising strategy to regulate fluid flow by modifying the porous microstructure, though their impact on transport dynamics remains insufficiently explored. This study investigates the role of hydrogel concentration and fluid viscosity in controlling flow behavior in paper membranes, relevant to diagnostics applications. Hydrogel is pre-imbibed into paper assays to modulate capillary transport, and the effects of varying injected fluid viscosities (0.954–1.54 cP, corresponding to solute concentrations of 0.055–0.555 M) and hydrogel concentrations (4.83–8.06 mg/mL) are examined across three distinct porous substrates. Real-time, high-resolution imaging enables quantitative analysis of fluid front evolution, including angular deviations, length variations, and interface curvature. Hydrogel presence increases flow resistance by 3-33.5%, while early-stage angular deviations reach up to 500% before stabilizing (reducing by 50-100%). Length deviations initially fluctuate (150-300%) but decline as imbibition progresses. Fluid front curvature also varies significantly (11-64%) in early stages. Viscous fluid enhances flow control, increasing resistance by 11-36% and reducing instability. Additionally, smaller pore sizes are found to improve flow uniformity. These findings offer new insights into hydrogel-mediated microfluidic regulation and pave the way for optimized, reproducible, and high-performance POC diagnostic systems.

Bacterial infections are a leading cause of mortality globally, and the timeliness of diagnosis is crucial for effective treatment. Traditional diagnostic methods, reliant on bacterial cultures, are often slow, leading to delays in treatment and increased mortality rates. To address delayed treatments, the study proposes a hybrid microfluidic device that employs deterministic lateral displacement (DLD) and dielectrophoresis (DEP) for rapid and continuous bacterial separation from blood cells. The research utilized COMSOL Multiphysics 5.6 to design and simulate the device, focusing on the optimization of various parameters such as pillar geometry, electrode geometry, fluid velocity, voltage, and DEP frequency. In order to calculate the separation efficiency, 120 particles along with the fluid were entered into the primary initial and the optimized hybrid device. The initial simulations yielded a separation efficiency of approximately 72% for bacteria and red blood cells (RBCs), and 100% for white blood cells (WBCs). After iterative optimization of the device’s design, including changes to the pillar geometries and electrode geometries and numbers, the separation efficiency for bacteria and RBCs was enhanced to 95%, while the efficiency for WBCs remained at 100%. These findings demonstrate the high efficiency of the designed microfluidic device in separating particles, indicating its potential to significantly reduce the time required for the detection of bacterial infections compared to conventional methods. The study presents a model of a microfluidic device that not only accelerates the diagnosis process but also maintains high separation efficiency, making it a promising tool for rapid point-of-care diagnostics.

The development of digital microfluidics has inspired significant advancements in diverse applications such as virus detection, molecular hybridization, and chemical reactions. The capabilities of digital microfluidics, taking Electrowetting-on-Dielectric (EWOD) for example, are precise handling and detecting targets based on the fundamental manipulations such as transportation, merging, mixing, and splitting of droplets. However, digital microfluidic systems suffer from complex electrode layouts, poor dynamic performance, and low-efficiency droplet manipulation. To address these limitations, we present a digital microfluidic system with enhanced dynamic properties using unidirectional emission surface acoustic waves. Surface acoustic wave device with resonance frequency of 300 MHz has been carefully designed with an acoustic reflector next to one end driving path from the other end, which is demonstrated as long as 600 times the wavelength for droplet transportation. By arranging the SAW array, the system enables precise and high-speed droplet transportation within a large programmed area. A smart platform is developed to automatically program and control droplets with preplanned routes. The SAW droplet manipulation system has shown excellent performance in high speed, ultra-long pathways, and automatic navigation, greatly promoting the acoustic manipulation advancements for biomedical research and chemical engineering.