Cortisol as a stress biomarker: analytical perspectives and challenges.

Hydrogels in head and neck cancer: Innovations and translational advances in research and therapy.

Double emulsions of water-in-oil-in-water (w1/o/w2) are critical for encapsulation and controlled release in microfluidic applications. In this work, double emulsion droplets were produced via a two-step flow-focusing process in a microchannel. A low-viscosity silicone oil (4.6 mPa s) was used as the oil phase, while the aqueous phase consisted of 48 wt% water and 52 wt% glycerol. Sodium dodecyl sulfate (SDS) was added at concentrations 0.2, 0.5, 1, and 2 times its critical micelle concentration (CMC = 11 mM) to systematically vary the interfacial tension. Three distinct formation regimes, namely drop-in-drop, drop-in-plug, and drop-in-thread, were identified under varying flow rate ratios and interfacial tensions. A semi-empirical model was developed to predict double droplet size in the drop-in-drop regime, which has significant practical relevance. For conditions with C/CMC ≥ 1, where interfacial tension is assumed to have reached equilibrium, good agreement with the experimental data was obtained, with mean absolute percentage errors (MAPE) of 8.16% for the core droplets and 9.54% for the double droplets. For lower surfactant concentrations, incorporating dynamic interfacial tension gave a MAPE of 8.17% for double droplet size prediction. These results provide a quantitative framework for droplet size prediction and offer operating guidance for the controlled generation of encapsulated droplets in microfluidic systems.

The establishment of monoclonal, stably transduced cell lines is a critical step in functional genomics and drug discovery. However, conventional methods are often time-consuming, labor-intensive, and prone to compromising cell viability. Here, we present a microfluidic single-cell sorting system based on laser-induced jetting (LIJet) that significantly improves the efficiency and quality of stable cell line generation. This system integrates a light-responsive substrate with metal coating and a PDMS microfluidic chip featuring an array of microwells, enabling single-cell capture, identification, and non-contact precision release. A 532nm nanosecond pulsed laser is used to generate localized microjets, which accurately eject target cells from the microwells. In addition to achieving a 100% sorting success rate and maintaining over 95.3% post-sorting cell viability, the system supports long-term on-chip culture and viral transduction with full real-time monitoring. We demonstrated the platform's functionality by performing on-chip ZsGreen lentiviral transduction of human lung adenocarcinoma PC9 cells, followed by fluorescence-based single-cell selection, ultimately establishing monoclonal cell lines with stable transgene expression. This platform offers notable advantages in low-damage manipulation, dynamic monitoring, and functional perturbation, providing a robust and efficient solution for the construction of stably transduced cell lines, gene function screening, and phenotypic analysis across a variety of biomedical applications.

Water pollution, particularly from heavy metals, poses a critical threat to ecosystems and human health. This study integrates the CRISPR-Cas12a system with MOF-based bio-barcode technology to create a platform for the rapid, real-time and on-site detection of multiple heavy metal ions, demonstrating exceptional sensitivity and selectivity. The detection limits for Cu2+, Pb2+, and Hg2+ are 0.26 nM, 0.06 nM, and 0.80 nM, respectively. Inductively coupled plasma-mass spectrometry analysis of real water samples confirmed the high accuracy and reliability of this method. Furthermore, a mobile phone-assisted portable device paired with a microfluidic chip facilitates real-time, rapid multi-channel metal ion detection in resource-limited settings.

N-Nitrosodimethylamine (NDMA) is a genotoxic nitrosamine that is commonly found in water due to its ready formation from commonly available precursor compounds. Routine monitoring of NDMA in water is challenging due to the need for complex sample preparation and instrumentation. Here, we propose the first example of an NDMA assay on a paper-based microfluidic platform. Moreover, it is the first study to integrate the required photochemical nitrosation reaction directly on-chip, enabling a complete photochemical-colorimetric workflow. The device is constructed with hollow PET capillary channels, double-sided adhesive, and glass fiber/paper pads with immobilized reagents, enabling sample analysis by simply dipping the device into water. On-chip detection of NDMA with sodium 1-naphthol-4-sulfonate is followed by Fe2+- and Co2+-based complexation, producing complementary green and red chromogenic signals. Its user-friendly dip-and-fold operation facilitates on-site, rapid, and high-frequency monitoring. The Fe2+- and Co2+-based channels provide linear detection ranges of 0-100 ppm and 0-30 ppm, with limits of detection of 4 ppm and 1.5 ppm, respectively. Interference studies, proper masking strategies, and dual-channel readout ensured high selectivity, while stability tests demonstrated excellent device stability over four weeks. Spike recovery experiments in tap, river, and lake water showed consistent recovery performance with RSD < 10%. This sustainable platform costs less than $0.2 per device, is compatible with smartphone-based readout, and offers a practical alternative to conventional analytical techniques. The findings presented here open possibilities to expand on-chip photochemical reactions in paper-based and other microfluidic systems for the detection of a broader range of contaminants.

Pressure-driven infiltration in capillary-opposed microchannels is commonly controlled through surface chemistry, while the role of channel geometry remains less understood. Here, we show that sinusoidal channel profiles can regulate liquid advancement by creating periodic capillary barriers that produce stepped meniscus motion under an applied pressure. We develop an analytical force-balance model that incorporates applied pressure, capillary forces, and viscous dissipation to predict conditions for interface advancement and arrest. High-speed synchrotron X-ray radiography of enclosed three-dimensional (3D)-printed microchannels confirms the predicted qualitative behavior, including successive arrest and release events during filling. Because the native printed material is near-neutral in wettability and does not sustain capillary-opposed flow, a conformal iCVD fluoropolymer coating was used to increase the contact angle to about 106°. Together, the model and experiments show that channel geometry can be used to tune pressure-driven infiltration independently of surface chemistry, establishing a geometric strategy for passive flow regulation in microfluidic systems.

The application of photocathodes in photoelectrochemical (PEC) devices is constrained by the low efficiency of light-induced electron-proton coupling and interfacial charge transfer. Herein, the nanoheterojunction structure formed by BiFeO3 and CuO exhibits broad visible-light absorption and an adjustable photogenerated carrier separation potential. Based on this, we demonstrate that rapid ion adsorption in copper hexacyanoferrate (CuFe HCF)-modified cathode materials in the liquid phase can significantly enhance electron coupling efficiency. Precise modulation of the electron-ion receptor characteristics of the cathode materials enables targeted optimization of the coupling process, thereby improving the separation and transport efficiency of photogenerated charge carriers in the ion-assisted photoelectrochemical (IAPEC) system for the target recognition response. Furthermore, the incorporation of a microfluidic system physically isolates the automatic sampling recognition zone from the photoelectrochemical detection zone, fully exposing the active sites of the photoelectrochemical cathode material for detection. The IAPEC biosensing achieves highly efficient detection of the marine pollutant okadaic acid toxin, featuring a low detection limit of 23.1 pg/mL and a broad linear range of 0.1-200 ng/mL. This dual-engineering strategy not only overcomes the long-standing limitations of standard PEC systems but also establishes a foundational framework for designing efficient biosensors for marine environmental monitoring.

Passive flow regulators enable autonomous, stable flow control without external electronics or active feedback. However, their dynamic response remains insufficiently investigated, limiting their potential integration into time-dependent fluidic circuits. Here, we present a reduced-order analytical framework based on an electrical analogy, along with systematic experimental characterization of a passive microfluidic flow regulator inspired by a fluidic transistor architecture. Devices with channel widths ranging from 300 to 700µm were fabricated using soft lithography to examine how geometry affects both the regulated flow rate and its transient response. Steady-state characterization revealed nonlinear flow-pressure relationships, with narrower channels exhibiting higher fluidic resistance and earlier onset of flow saturation. Dynamic characterization showed dominant first-order low-pass behavior governed by fluid-structure interactions within the elastofluidic network. The effective bandwidth decreases with increasing channel width, revealing a fundamental trade-off between throughput and transient response. Experimental data agreed well with the developed reduced-order fluidic resistance-capacitance model. Thus, geometry-dependent transient dynamics can be captured using compact, physically interpretable parameters without relying on a complex fluid-structure-interaction model. These findings establish quantitative geometry-dynamics relationships and provide practical design guides for integrating compliant flow-controlling elements into microfluidic circuits, lab-on-a-chip, and autonomous microfluidic systems with reliable and predictable dynamic performance.

Antiphospholipid syndrome (APS) is a platelet factor 4 (PF4)-centric immunothrombotic disorder.

Droplet digital enzyme-linked immunosorbent assay (ddELISA) enables ultrasensitive protein quantification; however, its performance is often limited by low single-bead encapsulation efficiency due to Poisson statistics and significant background interference from empty droplets. We present an integrated microfluidic system that overcomes both limitations through synergistic magneto-inertial manipulation (SMIM). By coupling an external magnetic field with laminar inertial focusing, the system applies coordinated hydrodynamic lift and magnetophoretic forces on immunomagnetic beads, thereby enabling three interdependent functions within a continuous workflow: ordered single-file bead focusing, high-throughput single-bead encapsulation, and active sorting of bead-containing droplets. Under optimized conditions (30 μL min-1; 300 mT), magnetic beads are focused into a stable single-file train with a lateral deviation of only 0.95 ± 1.21 μm. This deterministic ordering prior to droplet generation fundamentally overcomes the Poisson limit, achieving single-bead encapsulation efficiency of 81.31%─a 2.21-fold improvement over stochastic loading─and a total encapsulation efficiency of 91.11%. The integrated magnetic sorting module generates localized high-gradient fields, capturing bead-containing droplets with 93.97 ± 1.18% efficiency while eliminating >91% of empty droplets. The platform's quantitative capability was validated using a dual-color fluorescent bead assay (R2 = 0.9977; 0.50 - 1.75 × 107 beads mL-1) and an E. coli O157 ddELISA (R2 = 0.9999; LOD = 18.23 cells mL-1). This work establishes a fully integrated microfluidic platform that addresses the long-standing challenges of encapsulation inefficiency and empty-droplet interference in ddELISA by transforming bead encapsulation from a stochastic to a deterministic process, thereby providing a broadly applicable framework for high-throughput, single-particle-resolved digital bioanalysis.

Cellular mechanics play significant roles in biological processes from cellular level to tissue level. Great efforts have been committed to developing simple and reliable mechanical sensing strategies. Here, we present the concept of cellular mechanics displaying on visual structural color hydrogel microcolumn arrays. The microcolumn arrays were fabricated by using colloidal crystal pregel to hierarchically replicate microwell array templates. With the cultivation of beating cardiomyocytes, the microcolumn arrays could occur synchronous and reversible deformations, accompanied with visible structural color changes and reflection peak shifts for cellular mechanics displaying. Benefitting from this principle, together with the similar dimension with cells, the structural color microcolumn arrays could self-report the contraction force of cardiomyocytes at single-cell level. Based on these features, we have established a myocardial hypertrophy model in microfluidic systems and verify the value of the structural color hydrogel microcolumn arrays in monitoring the mechanical behaviors of cardiomyocytes under pathological conditions. Thus, we believe that the proposed structural color hydrogel microcolumn arrays and their integrated chips are suitable for evaluating clinical diseases of aberrant cellular force and even providing possible therapeutic targets.

Cell manipulation in microfluidic systems is essential for applications such as single-cell analysis, tissue engineering, and drug screening. Optoelectronic tweezers enable flexible, scalable, and non-contact cell manipulation. However, achieving automated closed-loop manipulation of multiple cells while avoiding collisions remains challenging in real microfluidic environments. Here, we present VPM-OET (Vision-guided Parallel Manipulation Optoelectronic Tweezers), a vision-guided closed-loop framework for robust parallel cell manipulation. The system combines computer vision-based detection, dynamic multi-target tracking, and collision-free trajectory planning to continuously monitor cell motion and update manipulation paths during operation. Using yeast cells and mammalian cells in microfluidic chips as model systems, we demonstrate cell transport around an obstacle region, parallel manipulation of 10 cells, and collision-free cross-path manipulation in separate experiments. This work offers a practical strategy for automated closed-loop OET control and expands the potential of parallel cell handling in microfluidic and biomedical applications.

Fully automated centrifugal microfluidic system for self-calibrating isothermal nucleic acid quantification.

An all-in-one microfluidic system via data-driven design for on-site genotyping of genetically modified foods.

Engineered biocatalysts enable highly selective chemical transformations with low environmental impact. Development of biocatalysts by directed evolution requires screening many enzyme variants for improved catalytic properties. The low throughput of commonly used label-free screening methods, e.g., liquid chromatography-mass spectrometry (LC-MS), becomes the rate-limiting step in biocatalyst development, limiting the coverage of protein sequence space explored. Direct MS methods have been applied to biocatalyst screening; however, these methods cannot be used to evaluate isomer selectivity. Ion mobility spectrometry is a separation technique readily combined with MS, facilitating isomer differentiation on the millisecond time scale. Here, we present a droplet microfluidic system coupled to cyclic ion mobility-mass spectrometry (cIM-MS) to enable the screening of isomeric products. The system was applied to the separation of biaryl benzofuran dimers formed by the fungal cytochrome P450 KtnC. The isomeric 5,7'-bibenzofuran and 7,7'-bibenzofuran products from KtnC variants were baseline-resolved within 32 ms by cIM. By infusing biocatalytic reaction mixtures as 5 nL droplets, an analysis throughput of 1.2 s/droplet was achieved using cIM-MS. Droplet cIM-MS was used to quantify standards in the reaction matrix with high agreement to actual concentrations of each isomer (i.e., R2 of 0.97 and 0.98 for total bibenzofuran content and fractional 5,7'-bibenzofuran content, respectively). For samples with enzymatically formed product isomers, droplet cIM-MS identified the same active variants and had comparable reproducibility (RSD of 10-15%) to analysis by LC-MS and produced this data 128 times faster. The method is expected to be suitable for improving the rate of biocatalyst development for isomer-selective reactions.

Heavy metal ion pollution has emerged as a global issue. These contaminants are not only present in water sources but are also commonly detected in air, soil, food, and consumer products, posing serious risks to ecosystems and human health. Even at very low concentrations, heavy metal ions can exhibit substantial toxicity. Traditional methods for the detection of heavy metal ions typically require complex laboratory equipment and specialized technicians, making them inadequate for rapid on-site monitoring. Microfluidic technology, as an innovative platform capable of precisely controlling and manipulating minute volumes of fluid, has demonstrated enormous potential in analytical chemistry, biomedicine, and environmental monitoring. In the rapidly developing field of microfluidics, paper-based microfluidic platforms have become prominent due to their low cost, straightforward fabrication, and eco-friendly nature, offering powerful tools for the detection of heavy metal ions in diverse samples. This survey consolidates the major advances reported from 2015 to 2025 in utilizing paper-based microfluidic systems for identifying heavy metal ion pollutants in diverse sample types, including air, explosive residues, water sources, herbal supplements, skin-whitening cosmetics, environmental aerosols, urine, soil, gunshot residues, cucumber plants, and food. The review analyzes in detail the principles and applications of detection strategies based on colorimetric methods, fluorescent methods, electrochemical methods, dual-detection systems, and other methods, as well as the role of nanomaterials and selective recognition elements in improving detection sensitivity and specificity. These portable, low-cost, and easy-to-operate detection systems provide viable solutions for environmental and public health monitoring, particularly suitable for resource-limited regions and scenarios requiring rapid detection.

Investigating the behavior, manipulation and transport of nanodroplets on the surface of solid films is critical for optimizing the functions of films and advancing diverse high-value applications across multiple fields. Using molecular dynamics simulations, we mainly investigate the moving behavior of water nanodroplets on the surface of MoS2/MoSe2 lateral heterostructure films. The results indicate that MoS2 exhibits more hydrophobic properties than the MoSe2 membrane, confirmed by the observation of a larger contact angle on the MoSe2 membrane. The van der Waals interactions were found to mainly dominate the wettability difference between MoS2 and MoSe2, where MoSe2 demonstrated a significantly stronger adsorption capacity for nanodroplets than MoS2. Based on this wettability difference, MoS2/MoSe2 lateral heterostructure films were designed to realize the directional migration, enrichment, and immobilization of water nanodroplets sequentially. Besides, effective regulation of the moving speed and direction of nanodroplets was achieved by constructing a MoS2/MoSe2 lateral heterostructure film with a wettability gradient. This research provides a theoretical basis and design insights for the development of microfluidic devices and droplet manipulation systems based on lateral heterostructures using two-dimensional transition metal chalcogenide materials.

Sweat is a rich biofluid whose composition depends heavily on physiology and varies systematically across a range of systemic and dermatological conditions, making it an attractive medium for non-invasive diagnostics. However, existing diagnostic tools, which rely primarily on electrochemical ion-selective electrodes and optical microfluidic systems, require complex instrumentation and have significant limitations in ease of application and deployment. This poses a need for a low-cost, simple sensing approach using sweat as a sample for disease detection. Here we demonstrate a novel bubble sensing methodology that exploits the relationship between bubble film stability and electrolyte concentration in a reagent-free setup requiring no electrochemical transduction. A controlled-volume bubble was made using a sodium dodecyl sulphate-glycerol solution, which was then tested by adding potassium chloride (KCl) solutions at concentrations of 0.01-0.15 mol L-1, simulating sweat at variable ionic strengths. Two characteristic timescales were identified: the time to burst (tb), measured by the naked eye on a seconds timescale, and the film retraction time (τ), resolved at 100 000 frames per second using a high-speed camera. The time to burst exhibited a strong exponential decay with increasing KCl concentration (R2 = 0.934), with greatest sensitivity in the healthy resting sweat range (0.01-0.1 mol L-1) and a plateau at pathological concentrations above 0.1 mol L-1. High-speed imaging revealed distinct changes in rupture initiation location and film retraction behaviour upon analyte addition, with retraction time increasing from 250 µs in control bubbles to ∼1.5 ms. The observed trend was quantitatively reproduced using a coupled DLVO-Kramers nucleation model, identifying electrostatic double-layer screening as the primary mechanism driving faster rupture at higher ionic strength. This work establishes the proof of concept for bubble rupture dynamics as a functional sensing mechanism and provides the basis for further development of surfactant bubble-based biosensors.

Silicon photonics has emerged as a promising technology for next-generation biosensors. Its CMOS compatibility, miniaturization, and large-scale fabrication capabilities, combined with high sensitivity, fast response, and inherent label-free detection capabilities, have positioned this technology at the forefront for the deployment of point-of-care (PoC) analytical platforms. However, operating a multiplexed photonic biosensor configuration remains challenging due to limitations such as efficient light coupling to multiple sensing elements, simultaneous signal acquisition, precise microfluidics and biofunctionalization, and optical crosstalk management between sensors. In this study, we introduce an interferometric biosensor that incorporates a new multiplexed nanophotonic bimodal waveguide (BiMW) chip with a compatible microfluidic system and an optimized light-coupling and readout configuration that enables simultaneous, individual detection of up to seven targets in the same sample. All system components have been incorporated into a compact prototype providing an outstanding bulk limit of detection (LOD) of (7 ± 5) × 10-7 RIU. The biosensor capabilities have been validated against a representative clinical scenario, demonstrating effective and sensitive detection of Respiratory Syncytial Virus (RSV) nucleoproteins relevant to infectious disease diagnostics, achieving a simultaneous LOD of 1.2 ± 0.4 ng·mL-1 across all seven sensors.