Microfluidics and Nanofluidics最新文献

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.

Liquid-liquid Extraction has emerged as a major technique for radioisotope extraction in recent years. This technique is particularly advantageous in the microscale as the surface-volume ratio is much larger. Since some of these radioisotopes have short half-lives, parallel flow in the microscale is used to extract them as it eliminates the need for separating the two fluids. Though such a configuration has been experimentally studied, dimensionless numbers have not been employed to understand the mass transfer mechanisms. This study uses three dimensionless numbers—the Biot, Peclet and Damkohler numbers—to delve deeper into mass transfer with a chemical reaction at the interface. Mass transfer simulations are performed using a Finite Difference model to solve the 2D Convection-Diffusion Equation with a first-order reaction at the interface, and these numbers are varied. The Damkohler number was observed to have the maximal impact on the extraction efficiency, and this was confirmed to be the case when the extraction efficiency didn’t change much as long as the Damkohler number was kept constant. In general, a higher Damkohler number results in a higher extraction efficiency and a correlation was proposed to quantify this influence.

Digital Micro Fluidic Biochips (DMFBs) are a revolutionary way to automate biochemical processes which are accurate, handy, and multifunctional. However, limitations in droplet manipulation, resource allocation, and assay execution continue to serve as considerable obstacles to effective sample preparation. Using electrical actuation techniques, these biochips accurately automate fluid sample analysis, simplifying essential laboratory tasks including cleaning, mixing, separating, and merging. Solutions with a predetermined target volume can be generated due to this technique. This process consists of combining various solutions of chemicals in a specified volume ratio by carrying out a different procedure. By using these methods, DMFBs can perform tests with little use of sample or reagent, opening up possibilities for use in drug research, gene sequencing, DNA analysis, medical diagnostics, and other fields. An extensive overview of optimization methods used for sample preparation in DMFBs is given in this paper, with an emphasis on algorithmic solutions that improve scheduling, dilution, and mixing. We categorize and evaluate current methods according to their computational methodologies and trade-offs between performance and adaptation to various biochip layouts. We also look at important issues, including real-time reconfiguration and waste droplet management. Lastly, we explore future research prospects in developing digital microfluidic biochip technologies and emphasize the suggested sample preparation scheduling method. The purpose of this survey is to assist researchers in creating DMFB sample preparation techniques that are more dependable and effective.