Droplet microfluidics for high-throughput biological assays

Rapid filamentous fungi gene knockout identification through high-throughput droplet microfluidics

Fungi are a diverse group of eukaryotic organisms, with over 1.5 million species inhabiting ecosystems worldwide. Many fungi grow as filaments (hyphae) and play critical ecological roles, both beneficial and harmful. Understanding their functions often requires generating knockout mutants and performing comparative analyses with wild-type strains. However, traditional methods for screening knockout mutants are labor-intensive, time-consuming, and limit the rapid identification of successful transformants. Here, we present a high-throughput droplet microfluidics platform capable of screening and sorting fungal transformants at single-cell resolution, significantly improving efficiency compared to conventional methods. The workflow involves encapsulating individual fungal transformants in pico-liter-volume water-in-oil emulsion droplets, culturing them in the presence of antibiotics, and identifying and sorting droplets containing transformants that exhibit hyphal growth. Transformants that grow in the presence of antibiotics are flagged as potential knockouts and then sorted out for confirmation through sequencing. This approach offers several advantages, including a 3-fold reduction in time for Fusarium graminearum protoplast growth until they can be distinguished from those exhibiting no growth, a screening throughput of up to 28,800 transformant-containing droplets per hour, and single-spore phenotyping to minimize post-processing requirements. Using this system, we successfully screened 24,000 F. graminearum transformants containing droplets, identified five potential transformants that exhibit growth on agar plates, of which two were confirmed via sequencing as true knockouts. These results demonstrate the utility of this droplet microfluidics-based platform as a powerful tool for accelerating fungal functional genomics and advancing our understanding of the ecological roles of fungi.

Droplet Microfluidics for Advanced Single-Cell Analysis

Droplet microfluidics has emerged as a breakthrough technology that is changing our comprehension of single-cell and their associated research. By separating individual cells within tiny droplets, ranging from nanoliters to picoliters using microfluidic devices, this innovative approach has revolutionized investigations at the single-cell level. Each of these droplets serves as a distinct experimental reaction vessel, enabling thorough exploration of cellular phenotypic variations, interactions between cells or cell-microorganisms as well as genomic insights. This review paper presents a comprehensive overview of the current state-of-the-art in droplet microfluidics, which has made single-cell analysis a practical approach for biological research. The review delves into the technological advancements in single-cell encapsulation techniques within droplet microfluidics, elucidating their applications in high-throughput single-cell screening, intercellular and cell-microorganism interactions, and genomic analysis. Furthermore, it discusses the advantages and constraints of droplet microfluidic technology, shedding light on critical factors such as throughput and versatile integration. Lastly, the paper outlines the potential avenues for future research in this rapidly evolving field.

Cap-Drop: A Pre-Programmed, Self-Powered Capillary Microfluidic System for Passive Droplet Generation and 3D Cell Culture Modeling

3D cell culture models and precision diagnostics have advanced significantly through microfluidic systems, yet their broad implementation remains limited by challenges in scalability, integration, and portability. Effective 3D cell culture models require systems that maintain sample integrity, minimize evaporation, and avoid crosstalk while handling various biofluids. However, current platforms often depend on active pumping, bulky components, and complex controls, which hinder portability, usability, and affordability. To address these challenges, the Capillary Droplet microfluidic (Cap-Drop) is presented, a novel capillary-driven platform that generates and immobilizes droplets with precision, eliminating the need for external pumps or intricate setups. Unlike conventional system, where moving droplets complicate tracking and identification, Cap-Drop ensures fixed droplet positioning, allowing seamless tracking and analysis. By integrating hydrophilic and hydrophobic materials with several innovative capillary elements -including passive vents (PV), pressure reducer (PR), stop valves (SV), delay channels, and bubble trap (BT)-Cap-Drop enables robust droplet formation (40 to 500 nL) for biofluids of varying properties. The pre-programmed design of PV in corporation with other capillary elements autonomously seals microwells (MWs), ensuring consistent sample digitization and supress risk of evaporation. Cap-Drop is optimized and offers a transformative platform for microfluidic technologies in mechanistic cellular studies, preclinical drug screening, and clinical diagnostics.

Single microorganism RNA sequencing of microbiomes using smRandom-Seq

Bacteria colonize nearly every part of the human body and various environments, displaying remarkable diversity. Traditional population-level transcriptomics measurements provide only average population behaviors, often overlooking the heterogeneity within bacterial communities. To address this limitation, we have developed a droplet-based, high-throughput single-microorganism RNA sequencing method (smRandom-seq) that offers highly species specific and sensitive gene detection. Here we detail procedures for microbial sample preprocessing, in situ preindexed cDNA synthesis, in situ poly(dA) tailing, droplet barcoding, ribosomal RNA depletion and library preparation. The main smRandom-seq workflow, including sample processing, in situ reactions and library construction, takes ~2 days. This method features enhanced RNA coverage, reduced doublet rates and minimized ribosomal RNA contamination, thus enabling in-depth analysis of microbial heterogeneity. smRandom-seq is compatible with microorganisms from both laboratory cultures and complex microbial community samples, making it well suited for constructing single-microorganism transcriptomic atlases of bacterial strains and diverse microbial communities. This Protocol requires experience in molecular biology and RNA sequencing techniques, and it holds promising potential for researchers investigating bacterial resistance, microbiome heterogeneity and host-microorganism interactions.

A mechanism for MEX-5-driven disassembly of PGL-3/RNA condensates in vitro

MEX-5 regulates the formation and dissolution of P granules in Caenorhabditis elegans embryos, yet the thermodynamic basis of its activity remains unclear. Here, using a time-resolved in vitro reconstitution system, we show that MEX-5 dissolves preassembled liquid-like PGL-3/RNA condensates by altering RNA availability and shifting the phase boundary. We develop a microfluidic assay to systematically analyze how MEX-5 influences phase separation. By measuring the contribution of PGL-3 to phase separation, we show that MEX-5 reduces the free energy of PGL-3, shifting the equilibrium toward dissolution. Our findings provide a quantitative framework for understanding how RNA-binding proteins modulate condensate stability and demonstrate the power of microfluidics in precisely mapping phase transitions.

Combining time domain modulation optofluidics and high dynamic range imaging for multiplexed, high throughput digital droplet assays

Digital enzyme-linked immunoassays (dELISA) have been successfully applied to the ultrasensitive quantification of analytes, including nucleic acids, proteins, cells, and extracellular vesicles, achieving robust detection limits in complex clinical specimens such as blood, and demonstrating utility across a broad range of clinical applications. The ultrasensitivity of dELISA comes from partitioning single analytes, captured onto a microbead, into millions of compartments so that they can be counted individually. There is particular interest in using dELISA for multiplexed measurements, but generating and detecting the billions of compartments necessary to perform multiplexed ultrasensitive dELISA remains a challenge. To address this, we have developed a high-throughput, optofluidic platform that performs quantitative fluorescence measurements on five populations of microbeads, each encoded with distinct ratios of two fluorescent dyes, for digital assays. The key innovation of our work is the parallelization of droplet generation and detection, combined with time-domain encoding of the excitation sources into distinct patterns that barcode the emission signal of both dyes within each bead, achieving high throughput (6 × 106 droplets/min) and accurate readout. Additionally, we modulate the exposure settings of the digital camera, capturing images of multiplexed beads and the droplet fluorescent substrate in consecutive frames, a method inspired by high dynamic range (HDR) photography. Our platform accurately classifies five populations of dual-encoded beads (accuracy > 99%) and detects bead-bound streptavidin-horseradish peroxidase molecules in a third fluorescence channel. This work establishes the technological foundation to combine high multiplexing and high throughput for droplet digital assays.

High-throughput strategies for monoclonal antibody screening: advances and challenges

Antibodies characterized by high affinity and specificity, developed through high-throughput screening and rapid preparation, are crucial to contemporary biomedical industry. Traditional antibody preparation via the hybridoma strategy faces challenges like low efficiency, long manufacturing cycles, batch variability and labor intensity. Advances in molecular biology and gene editing technologies offer revolutionary improvements in antibody production. New high-throughput technologies like antibody library display, single B cell antibody technologies, and single-cell sequencing have significantly cut costs and boosted the efficiency of antibody development. These innovations accelerate commercial applications of antibodies, meeting the biopharmaceutical industry's evolving demands. This review explores recent advancements in high-throughput development of antibody, highlighting their potential advantages over traditional methods and their promising future.

Technological advancement spurs Komagataella phaffii as a next-generation platform for sustainable biomanufacturing

Biomanufacturing stands as a cornerstone of sustainable industrial development, necessitating a shift toward non-food carbon feedstocks to alleviate agricultural resource competition and advance a circular bioeconomy. Methanol, a renewable one‑carbon substrate, has emerged as a pivotal candidate due to its abundance, cost-effectiveness, and high reduction potential, further bolstered by breakthroughs in CO₂ hydrogenation-based synthesis. Capitalizing on this momentum, the methylotrophic yeast Komagataella phaffii has undergone transformative technological upgrades, evolving from a conventional protein expression workhorse into an intelligent bioproduction chassis. This paradigm shift is fundamentally driven by converging innovations across CRISPR-empowered advancement in genome editing and AI-powered metabolic pathway design in K. phaffii. The integration of CRISPR systems with droplet microfluidics high-throughput screening has redefined strain engineering efficiency, achieving much higher editing precision than traditional homologous recombination while compressing the "design-build-test-learn" cycle. Concurrently, machine learning-enhanced genome-scale metabolic models facilitate dynamic flux balancing, enabling simultaneous improvements in product titers, carbon yields, and volumetric productivity. Finally, technological advancement promotes the application of K. phaffii, including directing more efficiently metabolic flux toward nutrient products, and strengthening efficient synthesis of excreted proteins. As DNA synthesis automation and robotic experimentation platforms mature, next-generation breakthroughs in genome modification, cofactor engineering, and AI-guided autonomous evolution will further cement K. phaffii as a next-generation platform for decarbonizing global manufacturing paradigms. This technological trajectory positions methanol-based biomanufacturing as a cornerstone of the low-carbon circular economy.

Hydrophilic/Omniphobic Droplet Arrays for High-throughput and Quantitative Enzymology

Engineered enzymes with enhanced or novel functions are specific catalysts with wide-ranging applications in industry and medicine. Here, we introduce droplet array microfluidic enzyme kinetics (DA-MEK), a high-throughput enzyme screening platform that combines water-in-air droplet microarrays formed on patterned superhydrophilic/omniphobic surfaces with cell-free protein synthesis to enable cost-effective expression and quantitative kinetic characterization of enzyme variants. By printing DNA templates encoding enzyme variants onto hydrophilic spots, stamping slides to add cell-free expression mix, and imaging the resulting arrays, we demonstrate reproducible expression of enzyme variants across hundreds of microwells per slide, with line of sight toward replicating this across larger libraries. By specifically patterning slides with antibodies, we further demonstrate parallel immobilization, purification, and iterative characterization of the expressed variants. Subsequent stamping of fluorogenic substrates and time-lapse imaging allows determination of Michaelis-Menten parameters for each variant, with measured catalytic efficiencies spanning 5 orders of magnitude and agreeing well with values obtained via traditional microtiter plate assays. DA-MEK consumes orders of magnitude less reagents than plate-based assays, while providing accurate and detailed kinetic information for both beneficial and deleterious mutations. In future work, we anticipate that DA-MEK will provide a powerful and versatile platform to accelerate enzyme engineering and enable screening of large variant libraries under diverse conditions.

Tunable Picoliter-Scale Dropicle Formation Using Amphiphilic Microparticles with Patterned Hydrophilic Patches

Microparticle-templated droplets or dropicles have recently gained interest in the fields of diagnostic immunoassays, single-cell analysis, and digital molecular biology. Amphiphilic particles have been shown to spontaneously capture aqueous droplets within their cavities upon mixing with an immiscible oil phase, where each particle templates a single droplet. Here, an amphiphilic microparticle with four discrete hydrophilic patches embedded at the inner corners of a square-shaped hydrophobic outer ring of the particle (4C particle) is fabricated. Three dimensional computational fluid dynamics simulations predict droplet formation dynamics and differing equilibrium conditions depending on the patterning configuration. Experiments recapitulate equilibrium conditions, enabling tunable dropicle configurations with reproducible volumes down to ≈200 pL templated by the amphiphilic particles. The dropicle configurations depend predominantly on the size of the hydrophilic patches of the 4C particles. This validates that the modeling approach can inform the design of dropicles with varying volumes and numbers per particle, which can be harnessed in new amplified bioassays for greater sensitivity, dynamic range, and statistical confidence.

Programming a bacterial biosensor for directed evolution of tryptophan hydroxylase via high-throughput droplet sorting

The modification of tryptophan hydroxylase (TPH) for the biosynthesis of 5-hydroxytryptophan (5-HTP) has recently become a focus of research. In this study, we established a droplet-based ultrahigh-throughput microfluidic screening platform (DTSP) to improve the industrial properties of TPH, whereas a bacterial biosensor for L-tryptophan (L-Trp) detection was engineered to improve sensitivity. The promoter pJ23111 achieved a strong negative correlation between the L-Trp concentration and the fluorescence output of the biosensor. The optimized DTSP platform was then utilized to screen superior TPH mutants by employing iterative saturation mutagenesis (ISM). The M4-1 variant (D129L/Q132M/P103A/T236K) demonstrated a 4.25-fold increase of catalytic activity compared to the parental CviPAH. Moreover, it exhibited excellent thermostability, with a 3.2-fold increase of half-life at 45 °C. Our study provides a reference for the development of bacterial biosensors for microdroplet-based screening platforms.

Biotechnological advances in 3D modeling of cancer initiation. Examples from pancreatic cancer research and beyond

In recent years, biofabrication technologies have garnered significant attention within the scientific community for their potential to create advancedin vitrocancer models. While these technologies have been predominantly applied to model advanced stages of cancer, there exists a pressing need to develop pertinent, reproducible, and sensitive 3D models that mimic cancer initiation lesions within their native tissue microenvironment. Such models hold profound relevance for comprehending the intricacies of cancer initiation, to devise novel strategies for early intervention, and/or to conduct sophisticated toxicology assessments of putative carcinogens. Here, we will explain the pivotal factors that must be faithfully recapitulated when constructing these models, with a specific focus on early pancreatic cancer lesions. By synthesizing the current state of research in this field, we will provide insights into recent advances and breakthroughs. Additionally, we will delineate the key technological and biological challenges that necessitate resolution in future endeavors, thereby paving the way for more accurate and insightfulin vitrocancer initiation models.

Droplets in open microfluidics: generation, manipulation, and application in cell analysis

Open droplet microfluidics is an emerging technology that generates, manipulates, and analyzes droplets in open configuration systems. Droplets function as miniaturized reactors for high-throughput analysis due to their compartmentalization and parallelization, while openness enables addressing and accessing the targeted contents. The convergence of two technologies facilitates the localization and intricate manipulation of droplets using external tools, showing great potential in large-scale chemical and biological applications, particularly in cell analysis. In this review, we first introduce various methods of droplet generation and manipulation in open environments. Next, we summarize the typical applications of open droplet systems in cell culture. Then, a comprehensive overview of cell analysis is provided, including nucleic acids, proteins, metabolites, and behaviors. Finally, we present a discussion of current challenges and perspectives in this field.

Microfluidics Based Particle and Droplet Generation for Gene and Drug Delivery Approaches

Microfluidics-based droplets have emerged as a powerful technology for biomedical research, offering precise control over droplet size and structure, optimal mixing of solutions, and prevention of cross-contamination. It is a major branch of microfluidic technology with applications in diagnostic testing, imaging, separation, and gene amplification. This review discusses the different aspects of microfluidic devices, droplet generation techniques, droplet types, and the production of micro/nano particles, along with their advantages and limitations. Passive and active methods for droplet formation are discussed, as well as the manipulation of droplet shape and content. This review also highlights the potential applications of droplet microfluidics in tissue engineering, cancer therapy, and drug delivery systems. The use of microfluidics in the production of lipid nanoparticles and polymeric microparticles is also presented, with emphasis on their potential in drug delivery and biomedical research. Finally, the contributions of microfluidics to vaccines, gene therapy, personalized medicine, and future perspectives are discussed, emphasizing the need for continuous innovation and integration with other technologies, such as AI and wearable devices, to further enhance its potential in personalized medicine and drug delivery. However, it is also noted that challenges in commercialization and widespread adoption still need to be addressed.

Design and fabrication of novel microfluidic-based droplets for drug screening on a chronic myeloid leukemia cell line

BACKGROUND

The challenges associated with traditional drug screening, such as high costs and long screening times, have led to an increase in the use of single-cell isolation technologies. Small sample volumes are required for high-throughput, cell-based assays to reduce assay costs and enable rapid sample processing. Using microfluidic chips, single-cell analysis can be conducted more effectively, requiring fewer reagents and maintaining biocompatibility. Due to the chip's ability to manipulate small volumes of fluid, high-throughput screening assays can be developed that are both miniaturized and automated. In the present study, we employ microfluidic chips for drug screening in chronic myeloid leukemia. This study aimed to establish a robust methodology integrating diverse assays, providing a holistic understanding of drug response.

MATERIAL AND METHODS

Herein, we have used a chronic myeloid leukemia derived cell line (K562) for drug screening with an innovative microfluidic-based drug screening approach to investigate the efficacy of imatinib in K562 cells. Cell viability was assessed using MTT assay. Apoptosis was measured using Annexin/PI staining by flow cytometry.

RESULTS

Significant increased apoptosis was seen in K562 cells treated with imatinib in the microfluidic device compared to cells treated with imatinib in 24- and 96-well plates. Moreover, in the microfluidic chip, drug screening time was reduced from 48 hours to 24 hours.

CONCLUSION

Compared to traditional approaches, microfluidic-based drug screening efficiently evaluates the efficacy of imatinib in K562 cells. This approach is promising for drug discovery and treatment optimization, as it increases sensitivity and streamlines the screening process.

Component library creation and pixel array generation with micromilled droplet microfluidics

Droplet microfluidics enable high-throughput screening, sequencing, and formulation of biological and chemical systems at the microscale. Such devices are generally fabricated in a soft polymer such as polydimethylsiloxane (PDMS). However, developing design masks for PDMS devices can be a slow and expensive process, requiring an internal cleanroom facility or using an external vendor. Here, we present the first complete droplet-based component library using low-cost rapid prototyping and electrode integration. This fabrication method for droplet microfluidic devices costs less than $12 per device and a full design-build-test cycle can be completed within a day. Discrete microfluidic components for droplet generation, re-injection, picoinjection, anchoring, fluorescence sensing, and sorting were built and characterized. These devices are biocompatible, low-cost, and high-throughput. To show its ability to perform multistep workflows, these components were used to assemble droplet "pixel" arrays, where droplets were generated, sensed, sorted, and anchored onto a grid to produce images.

Chaos-Assisted Production of Micro-Architected Spheres (CAPAS)

Hydrogel droplets with inner compartments are valuable in various fields, including tissue engineering. A droplet-based biofabrication method is presented for the chaos-assisted production of architected spheres (CAPAS) for the rapid generation of multilayered hydrogel spheres (ranging from 0.6 to 3.5 mm in diameter) at high-throughput rates (up to 2000 spheres per min). This method is based on the use of chaotic advection generated by a Kenics static mixer (KSM) nozzle. The configuration of the KSM (i.e., the number of mixing elements) determines the number of compartments within the sphere. Sphere size is adjusted by flow rate, printhead outlet diameter, polymer concentration (sodium alginate or gelatin-methacryloyl (GelMA)), and crosslinking bath composition. This versatile system operates in dripping and jetting modes, preserving multilayered architecture in both modes. Proof-of-concept experiments with breast cancer (MDA-MB-231), human dermal fibroblast (HDF), and murine myoblast (C2C12) lines show over 80% cell viability immediately post-fabrication, maintained over extended culture (14 or 30 days). CAPAS is used to create a breast cancer model with cancer-tissue-like and healthy-tissue-like micro-niches to test paclitaxel doses. It is envisioned that CAPAS will enable high-throughput fabrication of hydrogel spheres for tissue engineering, chemical engineering, and material sciences applications.

μREACT: A microfluidic system for rapid evaluation of trans-kingdom interactions

Trans-kingdom interactions between cells play pivotal roles in shaping intricate ecological and biological networks. However, our grasp of these interactions remains incomplete. Specifically, the vast phylogenetic spectrum of microorganisms capable of interacting with a given host cell type remains obscure, primarily due to the absence of efficient, high-throughput, single-cell resolution systems that can rapidly decipher these interactions. Here, we introduce μREACT (Microfluidic system for Rapid Evaluation of bacterial Adherence and Communication in Trans-kingdom interactions), a microfluidic system designed to analyze interkingdom interactions. μREACT not only unveiled both recognized and previously unknown interactions but also enabled their detailed characterization. The system features the use of microfluidic dielectrophoretic separation of bacteria that adhere to host cells at single-cell (digital) resolution, and enabled the sorting of 107 adherent microorganisms per hour, representing a comparable throughput to conventional flow cytometry systems, but without requiring any labeling. The analysis of soil microbial samples using μREACT revealed several bacterial species previously known to have high adherence to mammalian host cells, as well as new interactions involving strains that displayed hallmarks of emerging endosymbiosis. Taken together, μREACT serves as a formidable tool for identifying and characterizing webs of interkingdom interactions. Its implications extend beyond discovery of such interactions, where it has the potential to provide new insights into fundamental mechanisms driving ecosystem dynamics and biological processes.

Elucidating Extracellular Vesicle Isolation Kinetics via an Integrated Off-Stoichiometry Thiol-Ene and Cyclic Olefin Copolymer Microfluidic Device

Extracellular vesicles (EVs) are promising biomarkers for diagnosing complex diseases such as cancer and neurodegenerative disorders. Yet, their clinical application is hindered by challenges in isolating cancer-derived EVs efficiently due to their broad size distribution in biological samples. This study introduces a microfluidic device fabricated using off-stoichiometry thiol-ene and cyclic olefin copolymer, addressing the absorption limitations of polydimethylsiloxane (PDMS). The device streamlines a standard laboratory assay into a semi-automated microfluidic chip, integrating sample mixing and magnetic particle separation. Using the microfluidic device, the binding kinetics between EVs and anti-CD9 nanobodies were measured for the first time. Based on the binding kinetics, already after 10 min the EV capture was saturated and comparable to standard laboratory assays, offering a faster alternative to antibody-based immunomagnetic protocols. Furthermore, this study reveals the binding kinetics of EVs to anti-CD9 nanobodies for the first time. Our findings demonstrate the potential of the microfluidic device to enhance clinical diagnostics by offering speed and reducing manual labor without compromising accuracy.

Integrated Real-Time CMOS Luminescence Sensing and Impedance Spectroscopy in Droplet Microfluidics

High-throughput biosensor screening and optimization are critical for health and environmental monitoring applications to ensure rapid and accurate detection of biological and chemical targets. Traditional biosensor design and optimization methods involve labor-intensive processes, such as manual pipetting of large sample volumes, making them low throughput and inefficient for large-scale library screenings under various environmental and chemical conditions. We address these challenges by introducing a modular droplet microfluidic system embedded with custom CMOS integrated circuits (ICs) for impedance spectroscopy and bioluminescence detection. Fabricated in a 65 nm process, our CMOS ICs enable efficient droplet detection and analysis. We demonstrate successful sensing of luciferase enzyme-substrate reactions in nL-volume droplets. The impedance spectroscopy chip detects 4 nL droplets at 67 mm/s with a 45 pA resolution, while the luminescence detector senses optical signals from 38 nL droplets with a 6.7 nA/count resolution. We show real-time concurrent use of both detection methods within our hybrid platform for cross-validation. This system greatly advances conventional biosensor testing by increasing flexibility, scalability, and cost-efficiency.

Transformation gap from research findings to large-scale commercialized products in microfluidic field

The field of microfluidics has experienced rapid growth in the last several decades, yet it isn't considered to be a large industry comparable to semiconductor and consumer electronics. In this review, we analyzed the entire process of the transformation from research findings to commercialized products in microfluidics, as well as the significant gap during the whole developing process between microchip fabrication in R&D and large-scale production in the industry. We elaborated in detail on various materials in the microfluidics industry, including silicon, glass, PDMS, and thermoplastics, discussing their characteristics, production processes, and existing products. Despite challenges hindering the large-scale commercialization of microfluidic chips, ongoing advancements and applications are expected to integrate microfluidic technology into everyday life, transforming it into a commercially viable field with substantial potential and promising prospects.

An Acoustofluidic Picoinjector

Droplet microfluidics has emerged as a valuable technology for a multitude of chemical and biomedical applications, offering the capability to create independent microenvironments for high-throughput assays. Central to numerous droplet microfluidic applications is the picoinjection of materials into individual droplets, yet existing picoinjection methods often exhibit high power requirements, lack biocompatibility, and/or suffer from limited controllability. Here, we present an acoustofluidic picoinjector that generates acoustic pressure at the droplet interface to enable on-demand, energy-efficient, and biocompatible injection at high precision. We validate our platform by performing acid-base titrations by iteratively injecting picoliter volume reagents into droplets to induce pH transitions detectable by color change in solution. Additionally, we demonstrate the versatility of the acoustofluidic picoinjector in the synthesis of metallic nanoparticles, yielding highly monodisperse and reproducible particle morphologies compared to conventional bulk-phase techniques. By facilitating controlled delivery of reagents or biological samples with unparalleled accuracy, acoustofluidic picoinjection broadens the utility of droplet microfluidics for a myriad of applications in chemical and biological research.

Lab-In-Fiber Optofluidic Device for Droplet Digital Polymerase Chain Reaction (DdPCR) with Real-Time Monitoring

Droplet microfluidic systems have emerged as indispensable and advanced tools in contemporary biological science. A prominent example is the droplet digital polymerase chain reaction (ddPCR), which plays a pivotal role in next-generation sequencing and the detection of rare nucleic acids or mutations. However, existing optical detection configurations are bulky, intricate, and costly, and require meticulous optical alignment to optimize fluorescence sensing. Herein, we propose a lab-in-fiber optofluidic system (LiFO), which provides a stable and compact footprint, self-alignment, and enhanced optical coupling for high-accuracy ddPCR. Moreover, LiFO could expand its capabilities for multiangle-scattering light collection in which we collect focused forward-scattering light (fFSL) to enable real-time droplet counting and size monitoring. To accomplish these attributes, LiFO incorporates optical fibers, along with fabricated PDMS grooves, for a self-aligned optical setup to implement simultaneous fluorescence and scattering detection. Furthermore, LiFO harnesses the concept of flowing droplets functioning as microlenses, which allows us to collect and translate fFSL signals into droplet size information. We have demonstrated the effectiveness of LiFO in ddPCR applications, illustrating its capacity to enhance the accuracy and precision of DNA quantification. Notably, LiFO exhibits improved linearity in the measurement of serial DNA dilutions, reflected by an increase in R2 from 0.956 to 0.997. These results demonstrate the potential of LiFO to serve as a valuable tool across a wide spectrum of droplet microfluidic platforms, offering opportunities for advancement in practical applications.

Flow and clogging of capillary droplets

Capillary droplets form due to surface tension when two immiscible fluids are mixed. We describe the motion of gravity-driven capillary droplets flowing through narrow constrictions and obstacle arrays in both simulations and experiments. Our new capillary deformable particle model recapitulates the shape and velocity of single oil droplets in water as they pass through narrow constrictions in microfluidic chambers. Using this experimentally validated model, we simulate the flow and clogging of single capillary droplets in narrow channels and obstacle arrays and find several important results. First, the capillary droplet speed profile is nonmonotonic as the droplet exits the narrow orifice, and we can tune the droplet properties so that the speed overshoots the terminal speed far from the constriction. Second, in obstacle arrays, we find that extremely deformable droplets can wrap around obstacles, which leads to decreased average droplet speed in the continuous flow regime and increased probability for clogging in the regime where permanent clogs form. Third, the wrapping mechanism causes the clogging probability in obstacle arrays to become nonmonotonic with surface tension Γ. At large Γ, the droplets are nearly rigid and the clogging probability is large since the droplets can not squeeze through the gaps between obstacles. With decreasing Γ, the clogging probability decreases as the droplets become more deformable. However, in the small-Γ limit, the clogging probability increases since the droplets are extremely deformable and wrap around the obstacles. The results from these studies are important for developing a predictive understanding of capillary droplet flows through complex and confined geometries.

On-Demand Coalescence of Ferromagnetic Droplets in Microchannels Using an Oscillating Magnetic Field

Droplet-based microfluidics exhibit remarkable potential in achieving high-throughput chemical reactions with minimal reagent consumption. However, a pivotal challenge lies in the selective coalescence of droplets for precise process control, particularly when dealing with droplets of varying amounts and volumes, which are difficult to trap and coalesce due to their tiny dimensions and incessant movement. Hence, we proposed a method for on-demand coalescence of ferromagnetic droplets using an oscillating magnetic field. Experimental results show that the ferromagnetic droplets can be trapped in different positions in the microchannels according to the applied magnetic field intensity. A high-intensity pulsed amplitude of the magnetic field enables the migration of trapped droplets toward the same position, facilitating their mutual contact and interaction. By programmable modulation of the oscillating magnetic field, a controllable reciprocation of droplets in microchannels was successfully realized, which enabled us to dynamically capture, coalesce, and release two or more (≥3) droplets on demand. The integrated ferromagnetic droplet-based microfluidic platform allows contact-free, easily monitored, and on-demand coalescence of ferromagnetic droplets in microchannels, which holds promise for a wide range of applications, such as microfluidic-based drug synthesis, biosensing, reaction kinetics, and paracrine signaling, particularly.

Democratizing digital microfluidics by a cloud-based design and manufacturing platform

Akin to the impact that digital microelectronics had on electronic devices for information technology, digital microfluidics (DMF) was anticipated to transform fluidic devices for lab-on-a-chip (LoC) applications. However, despite a wealth of research and publications, electrowetting-on-dielectric (EWOD) DMF has not achieved the anticipated wide adoption, and commercialization has been painfully slow. By identifying the technological and resource hurdles in developing DMF chip and control systems as the culprit, we envision democratizing DMF by building a standardized design and manufacturing platform. To achieve this vision, we introduce a proof-of-concept cloud platform that empowers any user to design, obtain, and operate DMF chips (https://edroplets.org). For chip design, we establish a web-based EWOD chip design platform with layout rules and automated wire routing. For chip manufacturing, we build a web-based EWOD chip manufacturing platform and fabricate four types of EWOD chips (i.e., glass, paper, PCB, and TFT) to demonstrate the foundry service workflow. For chip control, we introduce a compact EWOD control system along with web-based operating software. Although industrial fabrication services are beyond the scope of this work, we hope this perspective will inspire academic and commercial stakeholders to join the initiative toward a DMF ecosystem for the masses.

Clear zone formation in microdroplets for high-throughput screening for lactic acid bacteria

Droplet microfluidic-based technology is a powerful tool for biotechnology, and it is also expected that it will be applied to culturing and screening methods. Using this technology, a new high-throughput screening method for lactic acid bacteria was developed. In this study, the conventional culture of lactic acid bacteria that form clear zones on an agar medium was reproduced in water-in-oil droplets, and only the droplets in which lactic acid bacteria grew were collected one by one. Using this method, the specific recovery of Lactiplantibacillus plantarum from a mixture of L. plantarum and Escherichia coli and the acquirement of lactic acid bacteria from an environmental sample were successful. This method could be applied to various conventional screening methods using the clear zone as a microbial growth indicator. This has expanded the possibilities of applying droplet microfluidic-based technology to microbial cultivations.

Robust Double Emulsions for Multicolor Fluorescence-Activated Cell Sorting

Cell-cell interactions are essential for the proper functioning of multicellular organisms. For example, T cells interact with antigen-presenting cells (APCs) through specific T-cell receptor (TCR)-antigen interactions during an immune response. Fluorescence-activated droplet sorting (FADS) is a high-throughput technique for efficiently screening cellular interaction events. Unfortunately, current droplet sorting instruments have significant limitations, most notably related to analytical throughput and complex operation. In contrast, commercial fluorescence-activated cell sorters offer superior speed, sensitivity, and multiplexing capabilities, although their use as droplet sorters is poorly defined and underutilized. Herein, we present a universally applicable and simple-to-implement workflow for generating double emulsions and performing multicolor cell sorting using a commercial FACS instrument. This workflow achieves a double emulsion detection rate exceeding 90%, enabling multicellular encapsulation and high-throughput immune cell activation sorting for the first time. We anticipate that the presented droplet sorting strategy will benefit cell biology laboratories by providing access to an advanced microfluidic toolbox with minimal effort and cost investment.

Efficient separation of large particles and giant cancer cells using an isosceles trapezoidal spiral microchannel

Polyploid giant cancer cells (PGCCs) contribute to the genetic heterogeneity and evolutionary dynamics of tumors. Their size, however, complicates their isolation from mainstream tumor cell populations. Standard techniques like fluorescence-activated cell sorting (FACS) rely on fluorescent labeling, introducing potential challenges in subsequent PGCC analyses. In response, we developed the Isosceles Trapezoidal Spiral Microchannel (ITSμC), a microfluidic device optimizing the Dean drag force (FD) and exploiting uniform vortices for enhanced separation. Numerical simulations highlighted ITSμC's advantage in producing robust FD compared to rectangular and standard trapezoidal channels. Empirical results confirmed its ability to segregate larger polystyrene (PS) particles (avg. diameter: 50 μm) toward the inner wall, while directing smaller ones (avg. diameter: 23 μm) outward. Utilizing ITSμC, we efficiently isolated PGCCs from doxorubicin-resistant triple-negative breast cancer (DOXR-TNBC) and patient-derived cancer (PDC) cells, achieving outstanding purity, yield, and viability rates (all greater than 90%). This precision was accomplished without fluorescent markers, and the versatility of ITSμC suggests its potential in differentiating a wide range of heterogeneous cell populations.

Coupling of droplet-on-demand microfluidcs with ESI/MS to study single-cell catalysis

Droplet microfluidics provides an efficient method for analysing reactions within the range of nanoliters to picoliters. However, the sensitive, label-free and versatile detection with ESI/MS poses some difficulties. One challenge is the difficult association of droplets with the MS signal in high-throughput droplet analysis. Hence, a droplet-on-demand system for the generation of a few droplets can address this and other problems such as surfactant concentration or cross-contamination. Accordingly, the system has been further developed for online coupling with ESI/MS. To achieve this, we developed a setup enabling on-demand droplet generation by hydrodynamic gating, with downstream microscopic droplet detection and MS analysis. This facilitated the incorporation of 1-9 yeast cells into individual 1-5 nL droplets and the monitoring of yeast-catalysed transformation from ketoester to ethyl-3-hydroxybutyrate by MS. With our method a mean production rate of 0.035 ± 0.017 fmol per cell per h was observed with a detection limit of 0.30 μM. In conclusion, our droplet-on-demand method is a versatile and advantageous tool for cell encapsulation in droplets, droplet imaging and reaction detection using ESI/MS.

Advances in Single-Cell Techniques for Linking Phenotypes to Genotypes

Single-cell analysis has become an essential tool in modern biological research, providing unprecedented insights into cellular behavior and heterogeneity. By examining individual cells, this approach surpasses conventional population-based methods, revealing critical variations in cellular states, responses to environmental cues, and molecular signatures. In the context of cancer, with its diverse cell populations, single-cell analysis is critical for investigating tumor evolution, metastasis, and therapy resistance. Understanding the phenotype-genotype relationship at the single-cell level is crucial for deciphering the molecular mechanisms driving tumor development and progression. This review highlights innovative strategies for selective cell isolation based on desired phenotypes, including robotic aspiration, laser detachment, microraft arrays, optical traps, and droplet-based microfluidic systems. These advanced tools facilitate high-throughput single-cell phenotypic analysis and sorting, enabling the identification and characterization of specific cell subsets, thereby advancing therapeutic innovations in cancer and other diseases.

All the single cells: if you like it then you should put some virus on it

Across a rich 70-year history, single-cell virology has revealed the impact of host and pathogen heterogeneity during virus infections. Recent technological innovations have enabled higher-resolution analyses of cellular and viral heterogeneity. Furthermore, single-cell analysis has revealed extreme phenotypes and provided additional insights into host-pathogen dynamics. Using a single-cell approach to explore fundamental virology questions, contemporary researchers have contributed to a revival of interest in single-cell virology with increased insights and enthusiasm.

Dielectrophoretic bead-droplet reactor for solid-phase synthesis

Solid-phase synthesis underpins many advances in synthetic and combinatorial chemistry, biology, and material science. The immobilization of a reacting species on the solid support makes interfacing of reagents an important challenge in this approach. In traditional synthesis columns, this leads to reaction errors that limit the product yield and necessitates excess consumption of the mobile reagent phase. Although droplet microfluidics can mitigate these problems, its adoption is fundamentally limited by the inability to controllably interface microbeads and reagent droplets. Here, we introduce Dielectrophoretic Bead-Droplet Reactor as a physical method to implement solid-phase synthesis on individual functionalized microbeads by encapsulating and ejecting them from microdroplets by tuning the supply voltage. Proof-of-concept demonstration of the enzymatic coupling of fluorescently labeled nucleotides onto the bead using this reactor yielded a 3.2-fold higher fidelity over columns through precise interfacing of individual microreactors and beads. Our work combines microparticle manipulation and droplet microfluidics to address a long-standing problem in solid-phase synthesis with potentially wide-ranging implications.

Harnessing elastic instabilities for enhanced mixing and reaction kinetics in porous media

Turbulent flows have been used for millennia to mix solutes; a familiar example is stirring cream into coffee. However, many energy, environmental, and industrial processes rely on the mixing of solutes in porous media where confinement suppresses inertial turbulence. As a result, mixing is drastically hindered, requiring fluid to permeate long distances for appreciable mixing and introducing additional steps to drive mixing that can be expensive and environmentally harmful. Here, we demonstrate that this limitation can be overcome just by adding dilute amounts of flexible polymers to the fluid. Flow-driven stretching of the polymers generates an elastic instability, driving turbulent-like chaotic flow fluctuations, despite the pore-scale confinement that prohibits typical inertial turbulence. Using in situ imaging, we show that these fluctuations stretch and fold the fluid within the pores along thin layers ("lamellae") characterized by sharp solute concentration gradients, driving mixing by diffusion in the pores. This process results in a [Formula: see text] reduction in the required mixing length, a [Formula: see text] increase in solute transverse dispersivity, and can be harnessed to increase the rate at which chemical compounds react by [Formula: see text]-enhancements that we rationalize using turbulence-inspired modeling of the underlying transport processes. Our work thereby establishes a simple, robust, versatile, and predictive way to mix solutes in porous media, with potential applications ranging from large-scale chemical production to environmental remediation.

Influenza A viral burst size from thousands of infected single cells using droplet quantitative PCR (dqPCR)

An important aspect of how viruses spread and infect is the viral burst size, or the number of new viruses produced by each infected cell. Surprisingly, this value remains poorly characterized for influenza A virus (IAV), commonly known as the flu. In this study, we screened tens of thousands of cells using a microfluidic method called droplet quantitative PCR (dqPCR). The high-throughput capability of dqPCR enabled the measurement of a large population of infected cells producing progeny virus. By measuring the fully assembled and successfully released viruses from these infected cells, we discover that the viral burst sizes for both the seasonal H3N2 and the 2009 pandemic H1N1 strains vary significantly, with H3N2 ranging from 101 to 104 viruses per cell, and H1N1 ranging from 101 to 103 viruses per cell. Some infected cells produce average numbers of new viruses, while others generate extensive number of viruses. In fact, we find that only 10% of the single-cell infections are responsible for creating a significant portion of all the viruses. This small fraction produced approximately 60% of new viruses for H3N2 and 40% for H1N1. On average, each infected cell of the H3N2 flu strain produced 709 new viruses, whereas for H1N1, each infected cell produced 358 viruses. This novel method reveals insights into the flu virus and can lead to improved strategies for managing and preventing the spread of viruses.

Fabrication of Crescent Shaped Microparticles for Particle Templated Droplet Formation

Crescent-shaped hydrogel microparticles are shown to template uniform volume aqueous droplets upon simple mixing with aqueous and oil media for various bioassays. This emerging "lab on a particle" technique requires hydrogel particles with tunable material properties and dimensions. The crescent shape of the particles is attained by aqueous two-phase separation of polymers followed by photopolymerization of the curable precursor. In this work, the phase separation of poly(ethylene glycol) diacrylate (PEGDA, Mw 700) and dextran (Mw 40 000) for tunable manufacturing of crescent-shaped particles is investigated. The particles' morphology is precisely tuned by following a phase diagram, varying the UV intensity, and adjusting the flow rates of various streams. The fabricated particles with variable dimensions encapsulate uniform aqueous droplets upon mixing with an oil phase. The particles are fluorescently labeled with red and blue emitting dyes at variable concentrations to produce six color-coded particles. The blue fluorescent dye shows a moderate response to the pH change. The fluorescently labeled particles are able to tolerate an extremely acidic solution (pH 1) but disintegrate within an extremely basic solution (pH 14). The particle-templated droplets are able to effectively retain the disintegrating particle and the fluorescent signal at pH 14.

Droplet digital molecular beacon-LAMP assay via pico-injection for ultrasensitive detection of pathogens

A pico-injection-aided digital droplet detection platform is presented that integrates loop-mediated isothermal amplification (LAMP) with molecular beacons (MBs) for the ultrasensitive and quantitative identification of pathogens, leveraging the sequence-specific detection capabilities of MBs. The microfluidic device contained three distinct functional units including droplet generation, pico-injection, and droplet counting. Utilizing a pico-injector, MBs are introduced into each droplet to specifically identify LAMP amplification products, thereby overcoming issues related to temperature incompatibility. Our methodology has been validated through the quantitative detection of Escherichia coli, achieving a detection limit as low as 9 copies/μL in a model plasmid containing the malB gene and 3 CFU/μL in a spiked milk sample. The total analysis time was less than 1.5 h. The sensitivity and robustness of this platform further demonstrated the potential for rapid pathogen detection and diagnosis, particularly when integrated with cutting-edge microfluidic technologies.

Microfluidics-assisted fabrication of natural killer cell-laden microgel enhances the therapeutic efficacy for tumor immunotherapy

Recently, interest in cancer immunotherapy has increased over traditional anti-cancer therapies such as chemotherapy or targeted therapy. Natural killer (NK) cells are part of the immune cell family and essential to tumor immunotherapy as they detect and kill cancer cells. However, the disadvantage of NK cells is that cell culture is difficult. In this study, porous microgels have been fabricated using microfluidic channels to effectively culture NK cells. Microgel fabrication using microfluidics can be mass-produced in a short time and can be made in a uniform size. Microgels consist of photo cross-linkable polymers such as methacrylic gelatin (GelMa) and can be regulated via controlled GelMa concentrations. NK92 cell-laden three-dimensional (3D) microgels increase mRNA expression levels, NK92 cell proliferation, cytokine release, and anti-tumor efficacy, compared with two-dimensional (2D) cultures. In addition, the study confirms that 3D-cultured NK92 cells enhance anti-tumor effects compared with enhancement by 2D-cultured NK92 cells in the K562 leukemia mouse model. Microgels containing healthy NK cells are designed to completely degrade after 5 days allowing NK cells to be released to achieve cell-to-cell interaction with cancer cells. Overall, this microgel system provides a new cell culture platform for the effective culturing of NK cells and a new strategy for developing immune cell therapy.

A facile single-cell patterning strategy based on harbor-like microwell microfluidics

Single-cell analysis is an effective method for conducting comprehensive heterogeneity studies ranging from cell phenotype to gene expression. The ability to arrange different cells in a predetermined pattern at single-cell resolution has a wide range of applications in cell-based analysis and plays an important role in facilitating interdisciplinary research by researchers in various fields. Most existing microfluidic microwell chips is a simple and straightforward method, which typically use small-sized microwells to accommodate single cells. However, this method imposes certain limitations on cells of various sizes, and the single-cell capture efficiency is relatively low without the assistance of external forces. Moreover, the microwells limit the spatiotemporal resolution of reagent replacement, as well as cell-to-cell communication. In this study, we propose a new strategy to prepare a single-cell array on a planar microchannel based on microfluidic flip microwells chip platform with large apertures (50 μm), shallow channels (50 μm), and deep microwells (50 μm). The combination of three configuration characteristics contributes to multi-cell trapping and a single-cell array within microwells, while the subsequent chip flipping accomplishes the transfer of the single-cell array to the opposite planar microchannel for cells adherence and growth. Further assisted by protein coating of bovine serum albumin and fibronectin on different layers, the single-cell capture efficiency in microwells is achieved at 92.1% ± 1%, while ultimately 85% ± 3.4% on planar microchannel. To verify the microfluidic flip microwells chip platform, the real-time and heterogeneous study of calcium release and apoptosis behaviours of single cells is carried out. To our knowledge, this is the first time that high-efficiency single-cell acquisition has been accomplished using a circular-well chip design that combines shallow channel, large aperture and deep microwell together. The chip is effective in avoiding the shearing force of high flow rates on cells, and the large apertures better allows cells to sedimentation. Therefore, this strategy owns the advantages of easy preparation and user-friendliness, which is especially valuable for researchers from different fields.

A Novel Microfluidics Droplet-Based Interdigitated Ring-Shaped Electrode Sensor for Lab-on-a-Chip Applications

This paper presents a comprehensive study focusing on the detection and characterization of droplets with volumes in the nanoliter range. Leveraging the precise control of minute liquid volumes, we introduced a novel spectroscopic on-chip microsensor equipped with integrated microfluidic channels for droplet generation, characterization, and sensing simultaneously. The microsensor, designed with interdigitated ring-shaped electrodes (IRSE) and seamlessly integrated with microfluidic channels, offers enhanced capacitance and impedance signal amplitudes, reproducibility, and reliability in droplet analysis. We were able to make analyses of droplet length in the range of 1.0-6.0 mm, velocity of 0.66-2.51 mm/s, and volume of 1.07 nL-113.46 nL. Experimental results demonstrated that the microsensor's performance is great in terms of droplet size, velocity, and length, with a significant signal amplitude of capacitance and impedance and real-time detection capabilities, thereby highlighting its potential for facilitating microcapsule reactions and enabling on-site real-time detection for chemical and biosensor analyses on-chip. This droplet-based microfluidics platform has great potential to be directly employed to promote advances in biomedical research, pharmaceuticals, drug discovery, food engineering, flow chemistry, and cosmetics.

A Label-Free Droplet Sorting Platform Integrating Dielectrophoretic Separation for Estimating Bacterial Antimicrobial Resistance

Antimicrobial resistance (AMR) has become a crucial global health issue. Antibiotic-resistant bacteria can survive after antibiotic treatments, lowering drug efficacy and increasing lethal risks. A microfluidic water-in-oil emulsion droplet system can entrap microorganisms and antibiotics within the tiny bioreactor, separate from the surroundings, enabling independent assays that can be performed in a high-throughput manner. This study presents the development of a label-free dielectrophoresis (DEP)-based microfluidic platform to sort droplets that co-encapsulate Escherichia coli (E. coli) and ampicillin (Amp) and droplets that co-encapsulate Amp-resistant (AmpR) E. coli with Amp only based on the conductivity-dependent DEP force (FDEP) without the assistance of optical analyses. The 9.4% low conductivity (LC) Luria-Bertani (LB) broth diluted with 170 mM mannitol can maintain E. coli and AmpR E. coli growth for 3 h and allow Amp to kill almost all E. coli, which can significantly increase the LCLB conductivity by about 100 μS/cm. Therefore, the AmpR E. coli/9.4%LCLB/Amp where no cells are killed and the E. coli/9.4%LCLB/Amp-containing droplets where most of the cells are killed can be sorted based on this conductivity difference at an applied electric field of 2 MHz and 100 Vpp that generates positive FDEP. Moreover, the sorting ratio significantly decreased to about 50% when the population of AmpR E. coli was equal to or higher than 50% in droplets. The conductivity-dependent DEP-based sorting platform exhibits promising potential to probe the ratio of AmpR E. coli in an unknown bacterial sample by using the sorting ratio as an index.

Microfluidics as an emerging paradigm for assisted reproductive technology: A sperm separation perspective

Millions of people are subject to infertility worldwide and one in every six people, regardless of gender, experiences infertility at some period in their life, according to the World Health Organization. Assisted reproductive technologies are defined as a set of procedures that can address the infertility issue among couples, culminating in the alleviation of the condition. However, the costly conventional procedures of assisted reproduction and the inherent vagaries of the processes involved represent a setback for its successful implementation. Microfluidics, an emerging tool for processing low-volume samples, have recently started to play a role in infertility diagnosis and treatment. Given its host of benefits, including manipulating cells at the microscale, repeatability, automation, and superior biocompatibility, microfluidics have been adopted for various procedures in assisted reproduction, ranging from sperm sorting and analysis to more advanced processes such as IVF-on-a-chip. In this review, we try to adopt a more holistic approach and cover different uses of microfluidics for a variety of applications, specifically aimed at sperm separation and analysis. We present various sperm separation microfluidic techniques, categorized as natural and non-natural methods. A few of the recent developments in on-chip fertilization are also discussed.

Deep learning-augmented T-junction droplet generation

Droplet generation technology has become increasingly important in a wide range of applications, including biotechnology and chemical synthesis. T-junction channels are commonly used for droplet generation due to their integration capability of a larger number of droplet generators in a compact space. In this study, a finite element analysis (FEA) approach is employed to simulate droplet production and its dynamic regimes in a T-junction configuration and collect data for post-processing analysis. Next, image analysis was performed to calculate the droplet length and determine the droplet generation regime. Furthermore, machine learning (ML) and deep learning (DL) algorithms were applied to estimate outputs through examination of input parameters within the simulation range. At the end, a graphical user interface (GUI) was developed for estimation of the droplet characteristics based on inputs, enabling the users to preselect their designs with comparable microfluidic configurations within the studied range.

Multifunctional Electrostatic Droplet Manipulation on the Femtosecond Laser-Prepared Slippery Surfaces

A strategy to manipulate droplets on the lubricated slippery surfaces using tribostatic electricity is proposed. By employing femtosecond laser-induced porous microstructures, we prepared a slippery surface with ultralow adhesion to various liquids. Electrostatic induction causes the charges within the droplet to be redistributed; thus, the droplet on the as-prepared slippery surfaces can be guided by electrostatic force under the electrostatic field, with controllable sliding direction and unlimited transport distance. The combination of electrostatic interaction and slippery surfaces allows us to manipulate droplets with a wide volume range (from 100 nL to 0.5 mL), charged droplets (including electrostatic attraction and repulsion), corrosive droplets, and even organic droplets with ultralow surface tension. In addition, droplets on tilted surfaces, curved surfaces, and inverted slippery surfaces can also be manipulated. Especially, the slippery surfaces can even allow the electrostatic interaction to manipulate alcohol with surface tension as low as 22.3 mN/m and liquid droplets suspended on a downward surface, which is not possible with reported superhydrophobic substrates. The features of slippery surfaces make the electrostatic manipulation successfully applied in versatile droplet manipulation, droplet patterning, chemical microreaction, transport of solid cargo, targeted delivery of chemicals, and liquid sorting.

Dynamic Manipulation of Droplets on Liquid-Infused Surfaces Using Photoresponsive Surfactant

Fast and programmable transport of droplets on a substrate is desirable in microfluidic, thermal, biomedical, and energy devices. Photoresponsive surfactants are promising candidates to manipulate droplet motion due to their ability to modify interfacial tension and generate "photo-Marangoni" flow under light stimuli. Previous works have demonstrated photo-Marangoni droplet migration in liquid media; however, migration on other substrates, including solid and liquid-infused surfaces (LIS), remains an outstanding challenge. Moreover, models of photo-Marangoni migration are still needed to identify optimal photoswitches and assess the feasibility of new applications. In this work, we demonstrate 2D droplet motion on liquid surfaces and on LIS, as well as rectilinear motion in solid capillary tubes. We synthesize photoswitches based on spiropyran and merocyanine, capable of tension changes of up to 5.5 mN/m across time scales as short as 1.7 s. A millimeter-sized droplet migrates at up to 5.5 mm/s on a liquid, and 0.25 mm/s on LIS. We observe an optimal droplet size for fast migration, which we explain by developing a scaling model. The model also predicts that faster migration is enabled by surfactants that maximize the ratio between the tension change and the photoswitching time. To better understand migration on LIS, we visualize the droplet flow using tracer particles, and we develop corresponding numerical simulations, finding reasonable agreement. The methods and insights demonstrated in this study enable advances for manipulation of droplets for microfluidic, thermal and water harvesting devices.

Microfluidic systems for infectious disease diagnostics

Microorganisms, encompassing both uni- and multicellular entities, exhibit remarkable diversity as omnipresent life forms in nature. They play a pivotal role by supplying essential components for sustaining biological processes across diverse ecosystems, including higher host organisms. The complex interactions within the human gut microbiota are crucial for metabolic functions, immune responses, and biochemical signalling, particularly through the gut-brain axis. Viruses also play important roles in biological processes, for example by increasing genetic diversity through horizontal gene transfer when replicating inside living cells. On the other hand, infection of the human body by microbiological agents may lead to severe physiological disorders and diseases. Infectious diseases pose a significant burden on global healthcare systems, characterized by substantial variations in the epidemiological landscape. Fast spreading antibiotic resistance or uncontrolled outbreaks of communicable diseases are major challenges at present. Furthermore, delivering field-proven point-of-care diagnostic tools to the most severely affected populations in low-resource settings is particularly important and challenging. New paradigms and technological approaches enabling rapid and informed disease management need to be implemented. In this respect, infectious disease diagnostics taking advantage of microfluidic systems combined with integrated biosensor-based pathogen detection offers a host of innovative and promising solutions. In this review, we aim to outline recent activities and progress in the development of microfluidic diagnostic tools. Our literature research mainly covers the last 5 years. We will follow a classification scheme based on the human body systems primarily involved at the clinical level or on specific pathogen transmission modes. Important diseases, such as tuberculosis and malaria, will be addressed more extensively.

Nanoparticle Assembly: From Self-Organization to Controlled Micropatterning for Enhanced Functionalities

Nanoparticles form long-range micropatterns via self-assembly or directed self-assembly with superior mechanical, electrical, optical, magnetic, chemical, and other functional properties for broad applications, such as structural supports, thermal exchangers, optoelectronics, microelectronics, and robotics. The precisely defined particle assembly at the nanoscale with simultaneously scalable patterning at the microscale is indispensable for enabling functionality and improving the performance of devices. This article provides a comprehensive review of nanoparticle assembly formed primarily via the balance of forces at the nanoscale (e.g., van der Waals, colloidal, capillary, convection, and chemical forces) and nanoparticle-template interactions (e.g., physical confinement, chemical functionalization, additive layer-upon-layer). The review commences with a general overview of nanoparticle self-assembly, with the state-of-the-art literature review and motivation. It subsequently reviews the recent progress in nanoparticle assembly without the presence of surface templates. Manufacturing techniques for surface template fabrication and their influence on nanoparticle assembly efficiency and effectiveness are then explored. The primary focus is the spatial organization and orientational preference of nanoparticles on non-templated and pre-templated surfaces in a controlled manner. Moreover, the article discusses broad applications of micropatterned surfaces, encompassing various fields. Finally, the review concludes with a summary of manufacturing methods, their limitations, and future trends in nanoparticle assembly.

The shape of things to come: Axisymmetric drop shape analysis using deep learning

HYPOTHESIS

In the traditional approach to Axisymmetric Drop Shape Analysis (ADSA), the determination of surface tension or interfacial tension is constrained by computational speed and image quality. By implementing a machine learning-based approach, particularly using a convolutional neural network (CNN), it is posited that analysis of pendant drop images can be both faster and more accurate.

EXPERIMENTS

A CNN model was trained and used to predict the surface tension of drop images. The performance of our CNN model was compared to the traditional ADSA, i.e. direct numerical integration, in terms of precision, computational speed, and robustness in dealing with images of varying quality. Additionally, the ability of the CNN model to predict other drop properties such as Volume and Surface Area was evaluated.

FINDINGS

Our CNN demonstrated a significant enhancement in experimental fit precision, predicting surface tension with an accuracy of (+/-) 1.22×10-1 mN/m and at a speed of 1.50 ms-1, outpacing the traditional method by more than 5×103 times. The model maintained an average surface tension error of 2.42×10-1 mN/m even for experimental images with challenges such as misalignment and poor focus. The CNN model also demonstrated showcased a high degree of accuracy in determining other drop properties.

Expanded Multiplexing on Sensor-Constrained Microfluidic Partitioning Systems

Microfluidics can split samples into thousands or millions of partitions, such as droplets or nanowells. Partitions capture analytes according to a Poisson distribution, and in diagnostics, the analyte concentration is commonly inferred with a closed-form solution via maximum likelihood estimation (MLE). Here, we present a new scalable approach to multiplexing analytes. We generalize MLE with microfluidic partitioning and extend our previously developed Sparse Poisson Recovery (SPoRe) inference algorithm. We also present the first in vitro demonstration of SPoRe with droplet digital PCR (ddPCR) toward infection diagnostics. Digital PCR is intrinsically highly sensitive, and SPoRe helps expand its multiplexing capacity by circumventing its channel limitations. We broadly amplify bacteria with 16S ddPCR and assign barcodes to nine pathogen genera by using five nonspecific probes. Given our two-channel ddPCR system, we measured two probes at a time in multiple groups of droplets. Although individual droplets are ambiguous in their bacterial contents, we recover the concentrations of bacteria in the sample from the pooled data. We achieve stable quantification down to approximately 200 total copies of the 16S gene per sample, enabling a suite of clinical applications given a robust upstream microbial DNA extraction procedure. We develop a new theory that generalizes the application of this framework to many realistic sensing modalities, and we prove scaling rules for system design to achieve further expanded multiplexing. The core principles demonstrated here could impact many biosensing applications with microfluidic partitioning.

Surface charging and electrophoretic behavior of conductive polymer micro-droplets in conductive polymer liquid solutions

This study investigates the surface charging and electrophoretic motion of polyethylene glycol-rich (PEG-rich) micro-droplets in dextran-rich solutions or dextran-rich micro-droplets in PEG-rich solutions. The electrophoretic velocities of the droplets were measured in a centimeter-sized chamber under an optical microscope. It was found that the direction of electrophoretic motion of both the PEG-rich droplets and dextran-rich droplets is opposite to the applied electric field, meaning that both the PEG-rich droplets and dextran-rich droplets are negatively charged. The electrophoretic velocity is independent of droplet size but proportional to the electric field strength. Increasing the NaCl concentration reduces the electrophoretic velocity of PEG-rich droplets and increases it for dextran-rich droplets, suggesting different surface charge changes due to ion affinity. The charge densities and velocities are affected by the PEG and dextran mass fractions. Physical models for droplet surface charging under different conditions were proposed to explain the experimental results.