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Abstract Chimeric antigen receptor (CAR) T cells are widely used to treat hematological tumors due to their powerful ability to target and kill cancer cells, of which accurate function evaluation at the single‐cell level is crucial to ensuring the efficacy of diagnosis and treatment. Currently, a universal platform to evaluate the efficacy of immune single cells rapidly, efficiently, and systematically is urgently needed. Here, the cytotoxicity, proliferative potential, and persistence of TIM3/CD28‐modified CD19 CAR‐T cells are evaluated in comparison with ordinary CD19 CAR‐T cells through high‐performance and throughput graphene oxide quantum dot (GOQD)‐based single‐cell microfluidic chips. Overall secretory factor expression, immune‐therapy effect of different effector‐target ratios, spatial immune‐therapy effects, and subgroup type profiling are demonstrated to explicit the immunotherapy effect of TIM3/CD28‐modified CD19 CAR‐T cells. TIM3/CD28‐modified CD19 CAR‐T cells show stronger anti‐tumor ability and maintain excellent immunotherapy effects even at low effector‐target ratios and remote distances. TIM3/CD28 also strengthens the local targeting ability of TIM3/CD28‐modified CD19 CAR‐T. Importantly, TIM3/CD28‐modified CD19 CAR‐T exhibits more distinct Th1/Th2 long‐term persistent and potent killer subgroups, which is very helpful for personalized therapy. Overall, this study provides a valuable approach that can be widely implemented to analyze current CAR‐T combinations and evaluate the function of innovative CAR treatments in the future.

Electrochemical surface‐enhanced Raman scattering (EC‐SERS) is a promising technique for the diagnosis of trace amounts of neurotransmitters, because it can elucidate neurotransmitters’ behavior on electrodes to deduce their functions in the human body. However, the current EC‐SERS devices need several tens of milliliters of analyte solution to collect enough signal for analysis. Miniaturization of EC‐SERS devices is crucial for the early diagnosis of disease and point‐of‐care testing. Herein, a new type of EC‐SERS sensor based on 3D microfluidic chips for the analysis of neurotransmitters in ultrasmall volumes is proposed. The microfluidic EC‐SERS chip is fabricated by a ship‐in‐a‐bottle technique based on hybrid laser processing. The working electrode is modified using silver/zinc oxide materials, enabling the formation of a unique “candy apple” structure. To assess the fabricated microfluidic EC‐SERS chips, ascorbic acid is analyzed using the ingenious microfluidic EC‐SERS chips to elucidate its redox reaction by EC‐SERS spectroscopy. Significantly, a sub‐10 μL volume of analyte solution is sufficient for EC‐SERS analysis, which is several orders smaller in volume than the requirements of current EC‐SERS devices. The unprecedented microfluidic EC‐SERS chips fabricated by the ship‐in‐a‐bottle integration technique can be used in portable and smart analyzers for next‐generation biomedicines and catalysts.

A novel optical-induced dielectrophoresis (ODEP) method employing a pressure-driven flow for the continuous separation of microparticles is presented in this study. By applying alternate current electric field on conductive indium tin oxide substrate and projecting the light geometry into the photoconductive layer, an inhomogeneous electric field is locally induced. The particles experience the dielectrophoretic force when passing through the lighting area, where the strongest electrical field gradient exists. By optimizing the structure of the lighting pattern, a stronger nonuniform electric field gradient is generated which predicts the separation of 1 and 3 µm polystyrene particles. Moreover, the effects of key parameters, including the light pattern geometry, applied voltage, and flow rate, were investigated in this study, leading to the successful sorting of 700 nm and 1 µm particles. To further examine the separation sensitivity and practicability of the proposed ODEP microfluidic method, the isolation of two different types of circulating tumor cells from T-cells and red blood cells are demonstrated, providing a novel method for the manipulation and separation of microparticles and nanoparticles., (© 2024 Wiley‐VCH GmbH.)

This study involved the design and fabrication of a microfluidic chip integrated with permalloy micromagnets. The device was used with aptamer-modified magnetic beads (MBs) of various sizes to successfully separate lung cancer cells from a mixture of other cells. The overall separation efficiency was evaluated based on the ratios of cells in the different outlets and inlets of the chip. The results showed efficiencies ranging from 43.4% to 50.2% for MB sizes between 1.36 and 4.50 µm. Interestingly, efficiency slightly decreased as the size of the MBs increased, contrary to predictions. Further examination revealed that larger MBs exerted gravitational force on the cell-bound MBs at low flow rates, causing the targets to settle before reaching the main microchannel region. This was attributed to fluidic resistance caused by a size mismatch between the inlet tube and the microfluidic conduit. An increase in cell accumulation at the inlet was observed with larger MB sizes due to gravity. Therefore, the definition of effective separation efficiency was revised to exclude the effect of cell accumulation at the inlet. Effective separation efficiencies were found to be 71.6%, 76.4%, and 79.4% for MB sizes of 1.36, 3.00, and 4.50 µm, respectively. The study concluded that larger MBs interacted more with the magnetic force, resulting in better separation. However, cells with smaller MBs were more likely to evade the magnetic force. The investigation provides valuable insights into isolating lung cancer cells using this method, with the potential for clinical application in cancer diagnosis and treatment., (© 2024 Wiley‐VCH GmbH.)

Single-cell multiomic and exosome analyses are potent tools in various fields, such as cancer research, immunology, neuroscience, microbiology, and drug development. They facilitate the in-depth exploration of biological systems, providing insights into disease mechanisms and aiding in treatment. Single-cell isolation, which is crucial for single-cell analysis, ensures reliable cell isolation and quality control for further downstream analyses. Microfluidic chips are small lightweight systems that facilitate efficient and high-throughput single-cell isolation and real-time single-cell analysis on- or off-chip. Therefore, most current single-cell isolation and analysis technologies are based on the single-cell microfluidic technology. This review offers comprehensive guidance to researchers across different fields on the selection of appropriate microfluidic chip technologies for single-cell isolation and analysis. This review describes the design principles, separation mechanisms, chip characteristics, and cellular effects of various microfluidic chips available for single-cell isolation. Moreover, this review highlights the implications of using this technology for subsequent analyses, including single-cell multiomic and exosome analyses. Finally, the current challenges and future prospects of microfluidic chip technology are outlined for multiplex single-cell isolation and multiomic and exosome analyses., (© 2024 The Authors. Advanced Science published by Wiley‐VCH GmbH.)

Hepatocellular carcinoma (HCC) is a highly lethal malignant tumor, and the current non-invasive diagnosis method based on serum markers, such as α-fetoprotein (AFP), and des-γ-carboxy-prothrombin (DCP), has limited efficacy in detecting it. Therefore, there is a critical need to develop novel biomarkers for HCC. Recent studies have highlighted the potential of exosomes as biomarkers. To enhance exosome enrichment, a silicon dioxide (SiO 2 ) microsphere-coated three-dimensional (3D) hierarchical porous chip, named a SiO 2 -chip is designed. The features of the chip, including its continuous porous 3D scaffold, large surface area, and nanopores between the SiO 2 microspheres, synergistically improved the exosome capture efficiency. Exosomes from both non-HCC and HCC subjects are enriched using an SiO 2 -chip and performed RNA sequencing to identify HCC-related long non-coding RNAs (lncRNAs) in the exosomes. This study analysis reveales that LUCAT-1 and EGFR-AS-1 are two HCC-related lncRNAs. To further detect dual lncRNAs in exosomes, quantitative real time polymerase chain reaction (qRT-PCR) is employed. The integration of dual lncRNAs with AFP and DCP significantly improves the diagnostic accuracy. Furthermore, the integration of dual lncRNAs with DCP effectively monitors the prognosis of patients with HCC and detects disease progression. In this study, a liquid biopsy-based approach for noninvasive and reliable HCC detection is developed., (© 2023 The Authors. Advanced Science published by Wiley‐VCH GmbH.)

Digital nucleic acid detection based on microfluidics technology can quantify the initial amount of nucleic acid in the sample with low equipment requirements and simple operations, which can be widely used in clinical and in vitro diagnosis. Recently, isothermal amplification technologies such as recombinase polymerase amplification (RPA), loop-mediated isothermal amplification (LAMP), and clustered regularly interspaced short palindromic repeats-CRISPR associated proteins (CRISPR-Cas) assisted technologies have become a hot spot of attention and state-of-the-art digital nucleic acid chips have provided a powerful tool for these technologies. Herein, isothermal amplification technologies including RPA, LAMP, and CRISPR-Cas assisted methods, based on digital nucleic acid microfluidics chips recently, have been reviewed. Moreover, the challenges of digital isothermal amplification and possible strategies to address them are discussed. Finally, future directions of digital isothermal amplification technology, such as microfluidic chip and device manufacturing, multiplex detection, and one-pot detection, are outlined., (© 2023 Wiley-VCH GmbH.)

Cell migration is an essential bioactive ceramics property and critical for bone induction, clinical application, and mechanism research. Standardized cell migration detection methods have many limitations, including a lack of dynamic fluid circulation and the inability to simulate cell behavior in vivo. Microfluidic chip technology, which mimics the human microenvironment and provides controlled dynamic fluid cycling, has the potential to solve these questions and generate reliable models of cell migration in vitro. In this study, a microfluidic chip is reconstructed to integrate the bioactive ceramic into the microfluidic chip structure to constitute a ceramic microbridge microfluidic chip system. Migration differences in the chip system are measured. By combining conventional detection methods with new biotechnology to analyze the causes of cell migration differences, it is found that the concentration gradients of ions and proteins adsorbed on the microbridge materials are directly related to the occurrence of cell migration behavior, which is consistent with previous reports and demonstrates the effectiveness of the microfluidic chip model. This model provides in vivo environment simulation and controllability of input and output conditions superior to standardized cell migration detection methods. The microfluidic chip system provides a new approach to studying and evaluating bioactive ceramics., (© 2023 Wiley-VCH GmbH.)

Super-resolution microscopy is rapidly developed in recent years, allowing biologists to extract more quantitative information on subcellular processes in live cells that is usually not accessible with conventional techniques. However, super-resolution imaging is not fully exploited because of the lack of an appropriate and multifunctional experimental platform. As an important tool in life sciences, microfluidics is capable of cell manipulation and the regulation of the cellular environment because of its superior flexibility and biocompatibility. The combination of microfluidics and super-resolution microscopy revolutionizes the study of complex cellular properties and dynamics, providing valuable insights into cellular structure and biological functions at the single-molecule level. In this perspective, an overview of the main advantages of microfluidic technology that are essential to the performance of super-resolution microscopy are offered. The main benefits of performing super-resolution imaging with microfluidic devices are highlighted and perspectives on the diverse applications that are facilitated by combining these two powerful techniques are provided., (© 2023 Wiley-VCH GmbH.)

Exosomes are promising new biomarkers for colorectal cancer (CRC) diagnosis, due to their rich biological fingerprints and high level of stability. However, the accurate detection of exosomes with specific surface receptors is limited to clinical application. Herein, an exosome enrichment platform on a 3D porous sponge microfluidic chip is constructed and the exosome capture efficiency of this chip is ≈90%. Also, deep mass spectrometry analysis followed by multi-level expression screenings revealed a CRC-specific exosome membrane protein (SORL1). A method of SORL1 detection by specific quantum dot labeling is further designed and the ensemble classification system is established by extracting features from 64-patched fluorescence images. Importantly, the area under the curve (AUC) using this system is 0.99, which is significantly higher (p < 0.001) than that using a conventional biomarker (carcinoembryonic antigen (CEA), AUC of 0.71). The above system showed similar diagnostic performance, dealing with early-stage CRC, young CRC, and CEA-negative CRC patients., (© 2023 Wiley-VCH GmbH.)

Precise detection involving droplets based on functional surfaces is promising for the parallelization and miniaturization of platforms and is significant in epidemic investigation, analyte recognition, environmental simulation, combinatorial chemistry, etc. However, a challenging and considerable task is obtaining mutually independent droplet arrays without cross-contamination and simultaneously avoiding droplet evaporation-caused quick reagent loss, inaccuracy, and failure. Herein, a strategy to generate mutually independent and hardly-volatile capsular droplet arrays using innovative mosaic patterned surfaces is developed. The evaporation suppression of the capsular droplet arrays is 1712 times higher than the naked droplet. The high evaporation suppression of the capsular droplet arrays on the surfaces is attributed to synergistic blocking of the upper oil and bottom mosaic gasproof layer. The scale-up of the capsular droplet arrays, the flexibility in shape, size, component (including aqueous, colloidal, acid, and alkali solutions), liquid volume, and the high-precision hazardous substance testing proves the concept's high compatibility and practicability. The mutually independent capsular droplet arrays with amazingly high evaporation suppression are essential for the new generation of high-performance open-surface microfluidic chips used in COVID-19 diagnosis and investigation, primary screening, in vitro enzyme reactions, environmental monitoring, nanomaterial synthesis, etc., (© 2023 Wiley-VCH GmbH.)

Secreted proteins provide abundant functional information on living cells and can be used as important tumor diagnostic markers, of which profiling at the single-cell level is helpful for accurate tumor cell classification. Currently, achieving living single-cell multi-index, high-sensitivity, and quantitative secretion biomarker profiling remains a great challenge. Here, a high-throughput living single-cell multi-index secreted biomarker profiling platform is proposed, combined with machine learning, to achieve accurate tumor cell classification. A single-cell culture microfluidic chip with self-assembled graphene oxide quantum dots (GOQDs) enables high-activity single-cell culture, ensuring normal secretion of biomarkers and high-throughput single-cell separation, providing sufficient statistical data for machine learning. At the same time, the antibody barcode chip with self-assembled GOQDs performs multi-index, highly sensitive, and quantitative detection of secreted biomarkers, in which each cell culture chamber covers a whole barcode array. Importantly, by combining the K-means strategy with machine learning, thousands of single tumor cell secretion data are analyzed, enabling tumor cell classification with a recognition accuracy of 95.0%. In addition, further profiling of the grouping results reveals the unique secretion characteristics of subgroups. This work provides an intelligent platform for high-throughput living single-cell multiple secretion biomarker profiling, which has broad implications for cancer investigation and biomedical research., (© 2022 Wiley-VCH GmbH.)

Cell mechanical forces play fundamental roles in regulating cellular responses to environmental stimulations. The shortcomings of conventional methods, including force resolution and cellular throughput, make them less accessible to mechanical heterogeneity at the single-cell level. Here, a DNA tensioner platform is introduced with high throughput (>10 000 cells per chip) and pN-level resolution. A microfluidic-based cell array is trapped on "hairpin-structured" DNA tensioners that enable transformation of the mechanical information of living cells into fluorescence signals. By using the platform, one can identify enhanced mechanical forces of drug-resistant cells as compared to their drug-sensitive counterparts, and mechanical differences between metastatic tumor cells in pleural effusion and nonmetastatic histiocytes. Further genetic analysis traces two genes, VEGFA and MINK1, that may play deterministic roles in regulating mechanical heterogeneities. In view of the ubiquity of cells' mechanical forces in the extracellular microenvironment (ECM), this platform shows wide potential to establish links of cellular mechanical heterogeneity to genetic heterogeneity., (© 2022 Wiley-VCH GmbH.)

Ultrathin, lightweight, flexible, and conformable interactive displays that transduce external stimuli into human-readable signals are essential for emerging applications, such as wearable electronics, human-machine interfaces, and soft robots. Herein, a biomolecule-interactive flexible light emitting capacitor (LEC) display (BIO-LEC) capable of dynamic and quantitative visualization of biomolecules through naked-eye detectable electroluminescence (EL) emission is reported. BIO-LEC comprises a coplanar LEC light source at the bottom, and a designed microfluidic chip as sampling compartment at the top. The quantitative measurement feature of BIO-LEC is achieved by introducing the top liquid electrode, which possesses a unique long dielectric realization time, in the microfluidic chip. BIO-LEC is novel for the following reasons, 1) simple stimuli response principle based on correlating EL intensity to dielectric properties of the top liquid electrode; 2) simple test conditions whereby no labeling is required in the analyte solution to optically detect biomolecules; 3) effective sampling method through the design of an integrated microfluidic chip for hosting the top liquid electrode, ensuring good reproducibility and preventing contamination; 4) sensitive detection limit for heparin concentrations at clinically relevant levels, and 5) high compliance with industrial manufacturing standards., (© 2021 Wiley-VCH GmbH.)

We herein develop a concentration gradient generator (CGG) on a microfluidic chip for diluting different nanoparticles. Specifically designed compact disk (CD)-shaped microchannels in the CGG module could thoroughly mix the flowing solutions and generate a linear concentration gradient of nanoparticles without aggregation. We combine the CGG with a single-cell trapper array (SCA) on microfluidics to evaluate the concentration-dependent bioeffects of the nanoparticles. The precise control of the spatiotemporal generation of nanoparticle concentration on the CGG module and the single-cell-level monitoring of the cell behaviors on the SCA module by a high-content system in real time, render the CGG-SCA system a highly precise platform, which can exclude the average effect of cell population and reflect the response of individual cells to the gradient concentrations accurately. In addition, the CGG-SCA system provides an automated platform for high-throughput screening of nanomedicines with high precision and low sample consumption., (© 2021 Wiley-VCH GmbH.)

Neurological disorders such as Alzheimer's disease, stroke, and brain cancers are difficult to treat with current drugs as their delivery efficacy to the brain is severely hampered by the presence of the blood-brain barrier (BBB). Drug delivery systems have been extensively explored in recent decades aiming to circumvent this barrier. In particular, polymeric nanoparticles have shown enormous potentials owing to their unique properties, such as high tunability, ease of synthesis, and control over drug release profile. However, careful analysis of their performance in effective drug transport across the BBB should be performed using clinically relevant testing models. In this review, polymeric nanoparticle systems for drug delivery to the central nervous system are discussed with an emphasis on the effects of particle size, shape, and surface modifications on BBB penetration. Moreover, the authors critically analyze the current in vitro and in vivo models used to evaluate BBB penetration efficacy, including the latest developments in the BBB-on-a-chip models. Finally, the challenges and future perspectives for the development of polymeric nanoparticles to combat neurological disorders are discussed., Competing Interests: The authors declare no conflict of interest., (© 2021 The Authors. Advanced Science published by Wiley‐VCH GmbH.)

The integration of microfluidics with biomedical research is confronted with considerable limitations due to its body materials. With high content of water, hydrogels own superior biocompatibility and degradability. Can hydrogels become another material choice for the construction of microfluidic chips, particularly biofluidics? The present review aims to systematically establish the concept of hydrogel-based microfluidic chips (HMCs) and address three main concerns: i) why choosing hydrogels? ii) how to fabricate HMCs?, and iii) in which fields to apply HMCs? It is envisioned that hydrogels may be used increasingly as substitute for traditional materials and gradually act as the body material for microfluidic chips. The modifications of conventional process are highlighted to overcome issues arising from the incompatibility between the construction methods and hydrogel materials. Specifically targeting at the "soft and wet" hydrogels, an efficient flowchart of "i) high resolution template printing; ii) damage-free demolding; iii) twice-crosslinking bonding" is proposed. Accordingly, a broader microfluidic chip concept is proposed in terms of form and function. Potential biomedical applications of HMCs are discussed. This review also highlights the challenges arising from the material replacement, as well as the future directions of the proposed concept. Finally, the authors' viewpoints and perspectives for this emerging field are discussed., (© 2020 Wiley-VCH GmbH.)

In the present study, cylindrical and laterally elongated pillar array columns were investigated for use in capillary electrochromatography. Minimal theoretical plate heights of H = 1.90 and 1.46 μm (in absence of sidewall effect) were obtained for coumarin C440 under unretained conditions for cylindrical and rectangular (laterally elongated, aspect ratio 4) pillar array columns, respectively. By comparing dispersion at the entire channel width to that at the central zone only, it appears that sidewall related dispersion significantly contributes to overall dispersion. A 40% reduction of the plate height was observed by taking into account only the central channel zone. A kinetic plot analysis was performed to evaluate the potential of the studied geometries by considering a maximum operating voltage of 20 kV as limiting parameter. It was demonstrated that rectangular radially elongated pillars produce a higher efficiency than cylindrical pillars and other microfabricated column structures for microchip capillary electrochromatography previously studied., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Minimal residual disease (MRD) offers a highly independent prognostic factor for leukemia patients. However, challenges confronting conventional MRD assays are high invasiveness, as well as limited detection sensitivity and clinical applicability. Inspired by the self-adaptive skeleton and multiple suckers or tendrils of climbing plants, a biomimetic Multivalent Aptamer Nanoclimber (MANC)-functionalized microfluidic chip (MANC-Chip) is reported for minimally invasive, highly sensitive and clinically applicable MRD detection in the peripheral blood of T-cell acute lymphoblastic leukemia patients. The MANCs are synthesized by a simple co-polymerization reaction. Due to their flexible structure and cooperative multivalent effect, MANCs dramatically enhance the binding affinity of aptamers targeting leukemia cells. A deterministic lateral displacement-patterned microfluidic chip is designed to further increase the collision probability between MANCs and leukemia cells. Benefiting from the synergistic effect of multivalent binding and enhanced collision, a high capture efficiency of 92.2% for leukemia cells is achieved. Moreover, the captured leukemia cells can be released with high efficiency of 88.9% and high viability of 93.8% via nuclease treatment prior to downstream analysis. Overall, the excellent features of MANC-Chip make it very useful for precise detection of MRD and better understanding of leukemia., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Screens of cancer stem cells (CSCs)-specific agents present significant challenges to conventional cell assays due to the difficulty in preparing CSCs ready for drug testing. To overcome this limitation, developed is a microfluidic single-cell assay for screening breast cancer stem cell-specific agents. This assay takes advantage of the single-cell clone-forming capability of CSCs, which can be specifically inhibited by CSC-targeting agents. The single-cell assay is performed on a microfluidic chip with an array of 3840 cell-capturing units; the single-cell arrays are easily formed by flowing a cell suspension into the microchip. Achieved is a single cell-capture rate of ≈60% thus allowing more than 2000 single cells to be analyzed in a single test. Over long-term suspension culture, only a minority of cells survive and form tumorspheres. The clone-formation rate of MCF-7, MDA-MB-231, and T47D cells is 1.67%, 5.78%, and 5.24%, respectively. The clone-forming inhibition assay is conducted by exposing the single-cell arrays to a set of anticancer agents. The CSC-targeting agents show complete inhibition of single-cell clone formation while the nontargeting ones show incomplete inhibition effects. The resulting microfluidic single-cell assay with the potential to screen CSC-specific agents with high efficiency provides new tools for individualized tumor therapy., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

As an interface between the blood flow and vessel wall, endothelial cells (ECs) are exposed to hemodynamic forces, and the biochemical molecules released from ECs-blood flow interaction are important determinants of vascular homeostasis. Versatile microfluidic chips have been designed to simulate the biological and physiological parameters of the human vascular system, but in situ and real-time monitoring of the mechanical force-triggered signals during vascular mechanotransduction still remains a significant challenge. Here, such challenge is fulfilled for the first time, by preparation of a flexible and stretchable electrochemical sensor and its incorporation into a microfluidic vascular chip. This allows simulating of in vivo physiological and biomechanical parameters of blood vessels, and simultaneously monitoring the mechanically induced biochemical signals in real time. Specifically, the cyclic circumferential stretch that is actually exerted on endothelium but is hard to reproduce in vitro is successfully recapitulated, and nitric oxide signals under normal blood pressure, as well as reactive oxygen species signals under hypertensive states, are well documented. Here, the first integration of a flexible electrochemical sensor into a microfluidic chip is reported, therefore paving a way to evaluate in vitro organs by built-in flexible sensors., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Exosomes are secreted by most cell types and circulate in body fluids. Recent studies have revealed that exosomes play a significant role in intercellular communication and are closely associated with the pathogenesis of disease. Therefore, exosomes are considered promising biomarkers for disease diagnosis. However, exosomes are always mixed with other components of body fluids. Consequently, separation methods for exosomes that allow high-purity and high-throughput separation with a high recovery rate and detection techniques for exosomes that are rapid, highly sensitive, highly specific, and have a low detection limit are indispensable for diagnostic applications. For decades, many exosome separation and detection techniques have been developed to achieve the aforementioned goals. However, in most cases, these two techniques are performed separately, which increases operation complexity, time consumption, and cost. The emergence of microfluidics offers a promising way to integrate exosome separation and detection functions into a single chip. Herein, an overview of conventional and microfluidics-based techniques for exosome separation and detection is presented. Moreover, the advantages and drawbacks of these techniques are compared., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Microfluidic chip electrophoresis has been widely employed for separation of various biochemical species owing to its advantages of low sample consumption, low cost, fast analysis, high throughput, and integration capability. In this article, we reviewed the development of four different modes of microfluidics-based electrophoresis technologies including capillary electrophoresis, gel electrophoresis, dielectrophoresis, and field (electric) flow fractionation. Coupling detection schemes on microfluidic electrophoresis platform were also reviewed such as optical, electrochemical, and mass spectrometry method. We further discussed the innovative applications of microfluidic electrophoresis for biomacromolecules (nucleic acids and proteins), biochemical small molecules (amino acids, metabolites, ions, etc.), and bioparticles (cells and pathogens) analysis. The future direction of microfluidic chip electrophoresis was predicted., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The fate of stem cells at the single cell level with limited communication with other cells is still unknown due to the lack of an efficient tool for highly accurate molecular detection. Moreover, the conditional sensitivity of biological experiments requires a sufficient number of parallel experiments to support a conclusion. In this work, a microfluidic single cell chip is designed for use with a protein chip to investigate the effect of hydroxyapatite (HAp) on the osteogenic differentiation of human adipose-derived stem cells (hADSCs) in situ at the single cell level. By successfully detecting secretory proteins in situ, it is found that the HAp nanorods enhance osteogenic differentiation at the single cell level. In the chip, the single cell seeding approach confirms the osteogenic differentiation of the hADSCs, which endocytoses HAp, by reducing the influence of the factors secreted by neighboring differentiating cells. Most importantly, more than 7000 microchambers provide a sufficient number of parallel experiments for statistical analysis, which ensure a high level of repeatability of the HAp nanorod-induced osteogenic differentiation. The microfluidic chip comprising single cell culture microchambers with in situ detection capability is a promising tool for research on cell behavior or cell fate at the single cell level., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Experimental setups to produce and to monitor model membranes have been successfully used for decades and brought invaluable insights into many areas of biology. However, they all have limitations that prevent the full in vitro mimicking and monitoring of most biological processes. Here, a suspended physiological bilayer-forming chip is designed from 3D-printing techniques. This chip can be simultaneously integrated to a confocal microscope and a path-clamp amplifier. It is composed of poly(dimethylsiloxane) and consists of a ≈100 µm hole, where the horizontal planar bilayer is formed, connecting two open crossed-channels, which allows for altering of each lipid monolayer separately. The bilayer, formed by the zipping of two lipid leaflets, is free-standing, horizontal, stable, fluid, solvent-free, and flat with the 14 types of physiologically relevant lipids, and the bilayer formation process is highly reproducible. Because of the two channels, asymmetric bilayers can be formed by making the two lipid leaflets of different composition. Furthermore, proteins, such as transmembrane, peripheral, and pore-forming proteins, can be added to the bilayer in controlled orientation and keep their native mobility and activity. These features allow in vitro recapitulation of membrane process close to physiological conditions., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydrogel structures equipped with internal microchannels offer more in vivo-relevant models for construction of tissues and organs in vitro. However, currently used microfabrication methods of constructing microfluidic devices are not suitable for the handling of hydrogel. This study presents a novel method of fabricating hydrogel-based microfluidic chips by combining the casting and bonding processes. A twice cross-linking strategy is designed to obtain a bonding interface that has the same strength with the hydrogel bulk, which can be applied to arbitrary combinations of hydrogels. It is convenient to achieve the construction of hydrogel structures with channels in branched, spiral, serpentine, and multilayer forms. The experimental results show that the combination of gelatin and gelatin methacrylate (GelMA) owns the best biocompatibility and can promote cell functionalization. Based on these, a vessel-on-a-chip system with vascular function in both physiological and pathological situations is established, providing a promising model for further investigations such as vascularization, vascular inflammation, tissue engineering, and drug development. Taken together, a facile and cytocompatible approach is developed for engineering a user-defined hydrogel-based chip that can be potentially useful in developing vascularized tissue or organ models., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Single-cell biology provides insights into some of the most fundamental processes in biology and promotes the understanding of life's mysteries. As the technologies to study single-cells expand, they will require sophisticated analytical tools to make sense of various behaviors and components of single-cells as well as their relations in the adherent tissue culture. In this paper, we revealed cell heterogeneity and uncovered the connections between cell adhesion strength and cell viability at single-cell resolution by extracting single adherent cells of interest from a standard tissue culture by using a microfluidic chip-based live single-cell extractor (LSCE). We believe that this method will provide a valuable new tool for single-cell biology., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Recently, a new observation method for monitoring of pH gradients in microfluidic free-flow electrophoresis has emerged. It is based on the use of chip-integrated fluorescent or luminescent micro sensor layers. These are able to monitor pH gradients in miniaturized separations in real time and spatially resolved; this is particularly useful in isoelectric focusing. Here these multifunctional microdevices that feature continuous separation, monitoring, and in some instances other functionalities, are reviewed. The employed microfabrication procedures to produce these devices are discussed and the different pH sensor matrices that were integrated and their applications in the separation of different types of biomolecules. The procedures for obtaining spatially resolved information about the separated molecules and the pH at the same time and different detection modalities to achieve this such as deep UV fluorescence as well as time-resolved referenced pH sensing and the integration of a precolumn labeling step into these platforms are also highlighted., (© 2017 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.)

The arterial microenvironment plays a vital role in the pathology of atherosclerosis (AS). However, the interplay between the arterial microenvironment and atherogenesis remains unclear, partially due to the gap between cell culture and animal experiments. Addressing this problem, the present study reports a microfluidic AS model reconstituting early-stage AS. Physiological or AS-prone hemodynamic conditions are recapitulated on the model. The on-chip model recaptures the atherogenic responses of endothelial cells (ECs) in ways that the Petri dish could not. Significant cytotoxicity of a clinical anti-atherosclerotic drug probucol is discovered on the model, which does not appear on Petri dish but is supported by previous clinical evidence. Moreover, the anti-AS efficiency of platinum-nanoparticles (Pt-NPs) on the model shows excellent consistency with animal experiments. The early-stage AS model shows an excellent connection between Petri dish and animal experiments and highlights its promising role in bridging fundamental AS research, drug screening, and clinical trials., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A catalytic polymer multilayer shell motor has been developed, which effects fast motion-based separation of charged organics in water. The shell motors are fabricated by sputtering platinum onto the exposed surface of silica templates embedded in Parafilm, followed by layer-by-layer assembly of polyelectrolyte multilayers to the templates. The catalytic shell motors display high bubble propulsion with speeds of up to 260 μm s(-1) (13 body lengths per second). Moreover, the polyelectrolyte multilayers assembled at high pH (pH>9.0) adsorb approximately 89% of dye molecules from water, owing to the electrostatic interaction between the positively charged polymers and the anionic dye molecules, and subsequently release them at neutral pH in a microfluidic device. The efficient propulsion coupled with the effective adsorption behavior of the catalytic shell motors in a microfluidic device results in accelerated separation of organics in water and thus holds considerable promise for water analysis., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A surface enhanced Raman scattering (SERS)-assisted 3D barcode chip has been developed for high-throughput biosensing. The 3D barcode is realized through joint 2D spatial encoding with the Raman spectroscopic encoding, which stores the SERS fingerprint information in the format of a 2D array. Here, the concept of SERS-assisted 3D barcode is demonstrated through multiplex immunoassay, where simultaneous detection of multiple targets in different samples has been achieved using a microfluidic platform. First, multiple proteins in different samples are spatially separated using a microfluidic patterned antibody barcode substrate, forming a 2D hybridization array. Then the SERS probes are used to identify and quantify the proteins. As different SERS probes are labeled with different Raman reporters, they could be employed as "SERS tags" to incorporate spectroscopic information into the 3D barcode. In this 3D barcode, the 2D spatial information helps to differentiate the samples and targets while the SERS information allows quantitative multiplex detection. It is found that the SERS-assisted 3D barcode chip can not only accomplish one-step multiplex detection within 30 min but also achieve an ultrasensitivity down to 10 fg mL(-1) (≈70 aM), which is expected to provide a promising tool for high-throughput biomedical applications., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)