An automated and portable microfluidic chemiluminescence immunoassay for quantitative detection of biomarkers

A programmable microfluidic platform to monitor calcium dynamics in microglia during inflammation

Neuroinflammation is characterized by the elevation of cytokines and adenosine triphosphate (ATP), which in turn activates microglia. These immunoregulatory molecules typically form gradients in vivo, which significantly influence microglial behaviors such as increasing calcium signaling, migration, phagocytosis, and cytokine secretion. Quantifying microglial calcium signaling in the context of inflammation holds the potential for developing precise therapeutic strategies for neurological diseases. However, the current calcium imaging systems are technically challenging to operate, necessitate large volumes of expensive reagents and cells, and model immunoregulatory molecules as uniform concentrations, failing to accurately replicate the in vivo microenvironment. In this study, we introduce a novel calcium monitoring micro-total analysis system (CAM-μTAS) designed to quantify calcium dynamics in microglia (BV2 cells) within defined cytokine gradients. Leveraging programmable pneumatically actuated lifting gate microvalve arrays and a Quake valve, CAM-μTAS delivers cytokine gradients to microglia, mimicking neuroinflammation. Our device automates sample handling and cell culture, enabling rapid media changes in just 1.5 s, thus streamlining the experimental workflow. By analyzing BV2 calcium transient latency to peak, we demonstrate location-dependent microglial activation patterns based on cytokine and ATP gradients, offering insights contrasting those of non-gradient-based perfusion systems. By harnessing advancements in microsystem technology to quantify calcium dynamics, we can construct simplified human models of neurological disorders, unravel the intricate mechanisms of cell-cell signaling, and conduct robust evaluations of novel therapeutics.

A review of SERS coupled microfluidic platforms: From configurations to applications

Microfluidic systems have attracted considerable attention due to their low reagent consumption, short analysis time, and ease of integration in comparison to conventional methods, but still suffer from shortcomings in sensitivity and selectivity. Surface enhanced Raman scattering (SERS) offers several advantages in the detection of compounds, including label-free detection at the single-molecule level, and the narrow Raman peak width for multiplexing. Combining microfluidics with SERS is a viable way to improve their detection sensitivity. Researchers have recently developed several SERS coupled microfluidic platforms with substantial potential for biomolecular detection, cellular and bacterial analysis, and hazardous substance detection. We review the current development of SERS coupled microfluidic platforms, illustrate their detection principles and construction, and summarize the latest applications in biology, environmental protection and food safety. In addition, we innovatively summarize the current status of SERS coupled multi-mode microfluidic platforms with other detection technologies. Finally, we discuss the challenges and countermeasures during the development of SERS coupled microfluidic platforms, as well as predict the future development trend of SERS coupled microfluidic platforms.

Recent developments and future perspectives of microfluidics and smart technologies in wearable devices

Wearable devices are gaining popularity in the fields of health monitoring, diagnosis, and drug delivery. Recent advances in wearable technology have enabled real-time analysis of biofluids such as sweat, interstitial fluid, tears, saliva, wound fluid, and urine. The integration of microfluidics and emerging smart technologies, such as artificial intelligence (AI), machine learning (ML), and Internet of Things (IoT), into wearable devices offers great potential for accurate and non-invasive monitoring and diagnosis. This paper provides an overview of current trends and developments in microfluidics and smart technologies in wearable devices for analyzing body fluids. The paper discusses common microfluidic technologies in wearable devices and the challenges associated with analyzing each type of biofluid. The paper emphasizes the importance of combining smart technologies with microfluidics in wearable devices, and how they can aid diagnosis and therapy. Finally, the paper covers recent applications, trends, and future developments in the context of intelligent microfluidic wearable devices.

Metal-enhanced fluorescence biosensor integrated in capillary flow-driven microfluidic cartridge for highly sensitive immunoassays

Point-of-care testing (POCT) for low-concentration protein biomarkers remains challenging due to limitations in biosensor sensitivity and platform integration. This study addresses this gap by presenting a novel approach that integrates a metal-enhanced fluorescence (MEF) biosensor within a capillary flow-driven microfluidic cartridge (CFMC) for the ultrasensitive detection of the Parkinson's disease biomarker, aminoacyl-tRNA synthetase complex interacting multi-functional protein 2 (AIMP-2). Crucial point to this approach is the orientation-controlled immobilization of capture antibody on a nanodimple-structured MEF substrate within the CFMC. This strategy significantly enhances fluorescence signals without quenching, enabling accurate quantification of low-concentration AIMP-2 using a simple digital fluorescence microscope with a light-emitting diode excitation source and a digital camera. The resulting platform exhibits exceptional sensitivity, achieving a limit of detection in the pg/mL range for AIMP-2 in human serum. Additionally, the CFMC design incorporates a capillary-driven passive sample transport mechanism, eliminating the need for external pumps and further simplifying the detection process. Overall, this work demonstrates the successful integration of MEF biosensing with capillary microfluidics for point-of-care applications.

Efficient Electrochemiluminescence Sensing in Microfluidic Biosensors: A Review

Microfluidic devices are capable of handling 10-9 L to 10-18 L of fluids by incorporating tiny channels with dimensions of ten to hundreds of micrometers, and they can be fabricated using a wide range of materials including glass, silicon, polymers, paper, and cloth for tailored sensing applications. Microfluidic biosensors integrated with detection methods such as electrochemiluminescence (ECL) can be used for the diagnosis and prognosis of diseases. Coupled with ECL, these tandem devices are capable of sensing biomarkers at nanomolar to picomolar concentrations, reproducibly. Measurement at this low level of concentration makes microfluidic electrochemiluminescence (MF-ECL) devices ideal for biomarker detection in the context of early warning systems for diseases such as myocardial infarction, cancer, and others. However, the technology relies on the nature and inherent characteristics of an efficient luminophore. The luminophore typically undergoes a redox process to generate excited species which emit energy in the form of light upon relaxation to lower energy states. Therefore, in biosensor design the efficiency of the luminophore is critical. This review is focused on the integration of microfluidic devices with biosensors and using electrochemiluminescence as a detection method. We highlight the dual role of carbon quantum dots as a luminophore and co-reactant in electrochemiluminescence analysis, drawing on their unique properties that include large specific surface area, easy functionalization, and unique luminescent properties.

A portable automated chip for simultaneous rapid point-of-care testing of multiple β-agonists

Abusive use of β-agonists as feed additives for animals and medication is detrimental to human health and food safety. Conventional assays are restricted to a single type of β-agonists detection and cannot match the multiplexing features to perform automated, high throughput, and rapid quantitative analysis in real samples. In this research, we develop a portable automated chip system (PACS) with highly integrated automated devices in conjunction with portable microfluidic chips to provide simultaneous point-of-care testing of multiple β-agonists in the field, simplifying complex manual methods, shortening assay times, and improving sensitivity. Specifically, silicon film is used as reaction substrates for immobilizing the conjugates of β-agonists to increase the sensitivity of the assay result. Then, the PACS with a chemiluminescence imaging detector is established for automatic high-throughput and sensitive detection of Clenbuterol, Ractopamine, and Salbutamol based on the indirect immunoassay. Newly developed chip with high mixing performance can improve the sensitivity of target determination. Multiplex assays were carried out using the developed system for Clenbuterol, Ractopamine, and Salbutamol with a limit of detection of 54 pg mL-1,59 pg mL-1, and 93 pg mL-1, respectively. Except for sample preparation and coating, the detection in the PACS takes less than 47 min. A satisfactory sample recovery (86.33%-108.12%) was obtained, validating the reliability and practical applicability of this PACS. Meanwhile, the PACS enables sensitive and rapid detection of multiple β-agonists in farms or markets where lacking advanced laboratory facilities.

Extending the Shelf-Life of Immunoassay-Based Microfluidic Chips through Freeze-Drying Sublimation Techniques

Point-of-care testing (POCT) platforms utilizing immunoassay-based microfluidic chips offer a robust and specific method for detecting target antibodies, demonstrating a wide range of applications in various medical and research settings. Despite their versatility and specificity, the adoption of these immunoassay chips in POCT has been limited by their short shelf-life in liquid environments, attributed to the degradation of immobilized antibodies. This technical limitation presents a barrier, particularly for resource-limited settings where long-term storage and functionality are critical. To address this challenge, we introduce a novel freeze-dry sublimation process aimed at extending the shelf-life of these microfluidic chips without compromising their functional integrity. This study elaborates on the mechanisms by which freeze-drying preserves the bioactivity of the immobilized antibodies, thereby maintaining the chip's performance over an extended period. Our findings reveal significant shelf-life extension, making it possible for these POCT platforms to be more widely adopted and practically applied, especially in settings with limited resources. This research paves the way for more accessible, long-lasting, and effective POCT solutions, breaking down previous barriers to adoption and application.

Artificial intelligence-driven electrochemical immunosensing biochips in multi-component detection

Electrochemical Immunosensing (EI) combines electrochemical analysis and immunology principles and is characterized by its simplicity, rapid detection, high sensitivity, and specificity. EI has become an important approach in various fields, such as clinical diagnosis, disease prevention and treatment, environmental monitoring, and food safety. However, EI multi-component detection still faces two major bottlenecks: first, the lack of cost-effective and portable detection platforms; second, the difficulty in eliminating batch differences and accurately decoupling signals from multiple analytes. With the gradual maturation of biochip technology, high-throughput analysis and portable detection utilizing the advantages of miniaturized chips, high sensitivity, and low cost have become possible. Meanwhile, Artificial Intelligence (AI) enables accurate decoupling of signals and enhances the sensitivity and specificity of multi-component detection. We believe that by evaluating and analyzing the characteristics, benefits, and linkages of EI, biochip, and AI technologies, we may considerably accelerate the development of EI multi-component detection. Therefore, we propose three specific prospects: first, AI can enhance and optimize the performance of the EI biochips, addressing the issue of multi-component detection for portable platforms. Second, the AI-enhanced EI biochips can be widely applied in home care, medical healthcare, and other areas. Third, the cross-fusion and innovation of EI, biochip, and AI technologies will effectively solve key bottlenecks in biochip detection, promoting interdisciplinary development. However, challenges may arise from AI algorithms that are difficult to explain and limited data access. Nevertheless, we believe that with technological advances and further research, there will be more methods and technologies to overcome these challenges.

A handheld plug-and-play microfluidic liquid handling automation platform for immunoassays

Lab-on-a-chip technologies and microfluidics have pushed miniaturized liquid handling to unprecedented precision, integration, and automation, which improved the reaction efficiency of immunoassays. However, most microfluidic immunoassay systems still require bulky infrastructures, such as external pressure sources, pneumatic systems, and complex manual tubing and interface connections. Such requirements prevent plug-and-play operation at the point-of-care (POC) settings. Here we present a fully automated handheld general microfluidic liquid handling automation platform with a plug-and-play 'clamshell-style' cartridge socket, a miniature electro-pneumatic controller, and injection-moldable plastic cartridges. The system achieved multi-reagent switching, metering, and timing control on the valveless cartridge using electro-pneumatic pressure control. As a demonstration, a SARS-CoV-2 spike antibody sandwich fluorescent immunoassay (FIA) liquid handling was performed on an acrylic cartridge without human intervention after sample introduction. A fluorescence microscope was used to analyze the result. The assay showed a limit of detection at 31.1 ng/mL, comparable to some previously reported enzyme-linked immunosorbent assays (ELISA). In addition to automated liquid handling on the cartridge, the system can operate as a 6-port pressure source for external microfluidic chips. A rechargeable battery with a 12 V 3000 mAh capacity can power the system for 42 h. The footprint of the system is 16.5 × 10.5 × 7 cm, and the weight is 801 g, including the battery. The system can find many other POC and research applications requiring complex liquid manipulation, such as molecular diagnostics, cell analysis, and on-demand biomanufacturing.

Toward Rapid and Accurate Molecular Diagnostics at Home

The global outbreaks of infectious diseases have significantly driven an imperative demand for rapid and accurate molecular diagnostics. Nucleic acid amplification tests (NAATs) feature high sensitivity and high specificity; however, the labor-intensive sample preparation and nucleic acid amplification steps remain challenging in order to carry out rapid and precision molecular diagnostics at home. This review discusses the advances and challenges of automatic solutions of sample preparation integrated with on-chip nucleic acid amplification for effective and accurate molecular diagnostics at home. The sample preparation methods of whole blood, urine, saliva/nasal swab, and stool on chip are examined. Then, the repurposable integrated sample preparation on a chip using various biological samples is investigated. Finally, the on-chip NAATs that can be integrated with automated sample preparation are evaluated. The user-friendly approaches with combined sample preparation and NAATs can be the game changers for next-generation rapid and precision home diagnostics.

Optical Detection of Cancer Cells Using Lab-on-a-Chip

The global need for accurate and efficient cancer cell detection in biomedicine and clinical diagnosis has driven extensive research and technological development in the field. Precision, high-throughput, non-invasive separation, detection, and classification of individual cells are critical requirements for successful technology. Lab-on-a-chip devices offer enormous potential for solving biological and medical problems and have become a priority research area for microanalysis and manipulating cells. This paper reviews recent developments in the detection of cancer cells using the microfluidics-based lab-on-a-chip method, focusing on describing and explaining techniques that use optical phenomena and a plethora of probes for sensing, amplification, and immobilization. The paper describes how optics are applied in each experimental method, highlighting their advantages and disadvantages. The discussion includes a summary of current challenges and prospects for cancer diagnosis.

Review of electrochemical and optical biosensors for testosterone measurement

Testosterone is an anabolic steroid and a major sex hormone in males. It plays vital roles, including developing the testis, penis, and prostate, increasing muscle and bone, and sperm production. In both men and women, testosterone levels should be in normal ranges. Besides, testosterone and its analogs are major global contributors to doping in sport. Due to the importance of testosterone testing, novel, accurate biosensors have been developed. This review summarizes the various methods for testosterone measurement. Also, recent optical and electrochemical approaches for the detection of testosterone and its analogs have been discussed.

Dual Direct Z-Scheme Heterojunction with Stable Electron Supply to a Au/PANI Photocathode for Ultrasensitive Photoelectrochemical and Electrochromic Visualization Detection of Ofloxacin in a Microfluidic Sensing Platform

A novel dual-mode microfluidic analytical device integrating self-powered photoelectrochemical (PEC) sensing with electrochromic visualization analysis was developed for ultrasensitive ofloxacin (OFL) detection. First, an advanced dual direct Z-scheme BiVO₄@Ni-ZnIn₂S₄/Bi₂S₃ (BVZIS) heterojunction was designed as a photoanode matrix to steadily provide electrons. The dual Z-scheme structure formed in photoactive BVZIS composites greatly accelerated the migration of electrons. In addition, the doping of Ni in ZnIn₂S₄ markedly enhanced the optical absorption and promoted the separation of the photocarrier. Second, electrochromic material polyaniline-modified Au (Au/PANI) was first electrodeposited on the photocathode for immobilizing aptamers and realizing visualized readout. On the one hand, Au/PANI with excellent conductivity could receive electrons from the photoanode without external energy supply. On the other hand, PANI would be rapidly reduced by the received electrons and change its color from blue to green obviously. With the increase in OFL, the increased steric hindrance resulted in the significant decline in the PEC signal and RGBgreen value. Third, wide linear ranges of PEC (0.05 pg/mL to 150 ng/mL) and electrochromic technique (0.1 pg/mL to 100 ng/mL) as well as low detection limits of PEC (18 fg/mL) and electrochromic (30 fg/mL) sensors could achieve the ultrasensitive detection of OFL in milk and river water.

Microfluidic on-chip valve and pump for applications in immunoassays

On-chip valves can simplify a microfluidic chip and make it easy to operate. However, most on-chip valves already reported still need complicated manufacture and sophisticated supporting devices. In this work, we present a straightforward on-chip valve, which can be serially connected, to form an on-chip pump. The liquid can horizontally flow one way by the regular deformations of flexure strips in the two valves at both sides of the chamber under pressure changes in microchannels generated by repeated vertical movements of linear actuators. The volume of this system including the chip and the supporting device is 0.65 cubic decimeters, which is much smaller than that of reported systems with a volume of at least 12 cubic decimeters, and the weight of this system is only 0.56 kg, making it possible for point-of-care testing. We carry out an immunoassay of folic acid on chip, and the results show satisfactory reproducibility with acceptable coefficients of variation. We determine 163 clinical human serum samples for folic acid. Furthermore, we detect transferrin, cobalamin and folic acid simultaneously on one chip with both sandwich and competitive binding immunoassay methods. We anticipate that this on-chip valve and pump can be applied in immunoassays and other biosensing applications.

Recent advancements in nucleic acid detection with microfluidic chip for molecular diagnostics

The coronavirus disease 2019 (COVID-19) has extensively promoted the application of nucleic acid testing technology in the field of clinical testing. The most widely used polymerase chain reaction (PCR)-based nucleic acid testing technology has problems such as complex operation, high requirements of personnel and laboratories, and contamination. The highly miniaturized microfluidic chip provides an essential tool for integrating the complex nucleic acid detection process. Various microfluidic chips have been developed for the rapid detection of nucleic acid, such as amplification-free microfluidics in combination with clustered regularly interspaced short palindromic repeats (CRISPR). In this review, we first summarized the routine process of nucleic acid testing, including sample processing and nucleic acid detection. Then the typical microfluidic chip technologies and new research advances are summarized. We also discuss the main problems of nucleic acid detection and the future developing trend of the microfluidic chip.

Portable general microfluidic device with complex electric field regulation functions for electrokinetic experiments

Electrokinetic sample manipulation is a key step for many kinds of microfluidic chips to achieve various functions, such as particle focusing and separation, fluid pumping and material synthesis. But these microfluidic experiments usually rely on large-scale signal generators for power supply, microscopes for imaging and other instruments for analysis, which hampers the portable process of microfluidic technology. Inspired by this situation, we herein designed a portable general microfluidic device (PGMD) with complex electric field regulation functions, which can accurately regulate static or continuous fluid samples. Through the graphical user interface (GUI) and modular design, the PGMD can generate multiple different electrical signals, and the micro-flow of fluid can be pumped through the built-in micropump, which can meet the requirements of most microfluidic experiments. Photos or videos of the microfluidic chip captured by the built-in microscope are received and displayed by a smartphone. We carried out a variety of microfluidic experiments such as induced-charge electroosmosis (ICEO), particle beam exit switching, thermal buoyancy flow and dielectrophoresis (DEP) on the PGMD. In addition, the PGMD can perform rapid microalgae concentration estimation in an outdoor environment, which can be used to guide microalgae cultivation, further demonstrating the development potential of this device in the field of microbial applications. Numerous results show that the PGMD has a high degree of integration and strong reliability, which expands the application of microfluidic electrokinetic experiments and provides technical support for the integration and portability of microfluidic experimental devices.

Designable microfluidic ladder networks from backstepping microflow analysis for mass production of monodisperse microdroplets

Controllable mass production of monodisperse droplets plays a key role in numerous fields ranging from scientific research to industrial application. Microfluidic ladder networks show great potential in mass production of monodisperse droplets, but their design with uniform microflow distribution remains challenging due to the lack of a rational design strategy. Here an effective design strategy based on backstepping microflow analysis (BMA) is proposed for the rational development of microfluidic ladder networks for mass production of controllable monodisperse microdroplets. The performance of our BMA rule for rational microfluidic ladder network design is demonstrated by using an existing analogism-derived rule that is widely used for the design of microfluidic ladder networks as the control group. The microfluidic ladder network designed by the BMA rule shows a more uniform flow distribution in each branch microchannel than that designed by the existing rule, as confirmed by single-phase flow simulation. Meanwhile, the microfluidic ladder network designed by the BMA rule allows mass production of droplets with higher size monodispersity in a wider window of flow rates and mass production of polymeric microspheres from such highly monodisperse droplet templates. The proposed BMA rule provides new insights into the microflow distribution behaviors in microfluidic ladder networks based on backstepping microflow analysis and provides a rational guideline for the efficient development of microfluidic ladder networks with uniform flow distribution for mass production of highly monodisperse droplets. Moreover, the BMA method provides a general analysis strategy for microfluidic networks with parallel multiple microchannels for rational scale-up.

Dual-CRISPR/Cas12a-Assisted RT-RAA for Ultrasensitive SARS-CoV-2 Detection on Automated Centrifugal Microfluidics

The clustered regularly interspaced short palindromic repeats (CRISPR)-based nucleic acid detection can be combined with recombinase-aided amplification (RAA) to enable rapid, accurate, and early detection of SARS-CoV-2. Current CRISPR-based approaches to detecting viral nucleic acid typically require immense manual operations to transfer RPA amplicons for CRISPR detection or suffer from compromised sensitivity by mixing the competing RPA amplification and CRISPR detection. Here, we develop dual-CRISPR/Cas12a-assisted RT-RAA assay and a ″sample-to-answer″ centrifugal microfluidic platform that can automatically detect 1 copy/μL of the SARS-CoV-2 within 30 min. This chip separates the amplification (RAA) from detection (CRISPR), such that sensitivity is maximized and the time consumption is decreased by a factor of 3. For the 26 positive and 8 negative clinical SARS-CoV-2 samples, this automated centrifugal microfluidics achieved 100% accuracy compared to the gold-standard RT-PCR technique. This point-of-care test, with the advantages of being one-step, automated, rapid, and sensitive, will have a significant potential for clinical diagnosis and disease prevention.

Automated Centrifugal Microfluidic Chip Integrating Pretreatment and Molecular Diagnosis for Hepatitis B Virus Genotyping from Whole Blood

Point-of-care (POC) testing for nucleic acid that combines pretreatment and molecular diagnosis is crucial in analyzing complex samples such as those encountered in clinical diagnosis. Herein, we developed a centrifugal microfluidic platform, which can achieve a series of functions including separating serum and adsorbing, washing, eluting, and detecting DNA. We combined multiple signal enhancement systems including recombinase polymerase amplification (RPA), T7 transcription technology, and clustered regularly interspaced short palindromic repeat (CRISPR) technology to yield an ultrabright signal, which can avoid false-negative results. As an application, hepatitis B virus (HBV), a virus that causes global public health problems, was successfully detected and genotyped from whole blood on the automated centrifugal microfluidic platform. Compared to the traditional diagnosis process, the POC platform largely decreased the consumption of time from 3 to 1 h and the consumption of professional labor from three persons to only one. The automated centrifugal microfluidic platform integrated pretreatment and molecular diagnosis will play an essential role in clinical detection.

Active droplet-array microfluidics-based chemiluminescence immunoassay for point-of-care detection of procalcitonin

The application of conventional chemiluminescence immunoassay (CLIA) in resource-limited settings is limited due to the large apparatus footprint, cumbersome operation and maintenance process, and high consumption of reagents. To address this issue, we developed an active droplet-array (ADA) microfluidics-based CLIA system, which consists of a compact microchip analyzer and microfluidic chips with preloaded reagents. The microfluidic chip contains microslit-connected microchambers, in which all the required reagents were preloaded in water-in-oil droplets. The microfluidic chip analyzer can manipulate five microfluidic chips in parallel in a single run. By interacting the microchip with magnetic, thermal, optical mechanisms programmatically, the entire workflow of CLIA can be accomplished in an automated manner. With the proposed CLIA, the detection of procalcitonin (PCT) can be completed in 12 min, with a limit of detection (LOD) of 0.044 ng mL^-1 and a detection range from 0.044 to 100 ng mL^-1. We found a good linear correlation between the microfluidic CLIA and the conventional electrochemiluminescence immunoassay (R²=0.98).The microfluidic CLIA has significant advantages over the conventional ELISA in detection sensitivity, dynamic range, instrument size and turnaround time, and can provide more consistent and reliable results than the lateral flow immunoassays. The compact microfluidic system can perform automated and parallelized CLIA in a short turnaround time, and thus well suited to Point-of-Care detection of disease biomarkers.

Protein and mRNA Quantification in Small Samples of Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes in 96-Well Microplates

We describe a method for protein quantification and for mRNA quantification in small sample quantities of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Demonstrated here is how the capillary-based protein detection system Wes™ by ProteinSimple and the Power SYBR™ Green Cells-to-CT™ Kit by Invitrogen can be applied to individual samples in a 96-well microplate format and thus made compatible with high-throughput (HT) cardiomyocyte assays. As an example of the usage, we illustrate that Cx43 protein and GJA1 mRNA levels in hiPSC-CMs are enhanced when the optogenetic actuator, channelrodopsin-2 (ChR2), is genetically expressed in them. Instructions are presented for cell culture and lysate preparations from hiPSC-CMs, along with optimized parameter settings and experimental protocol steps. Strategies to optimize primary antibody concentrations as well as ways for signal normalization are discussed, i.e., antibody multiplexing and total protein assay. The sensitivity of both the Wes and Cells-to-CT kit enables protein and mRNA quantification in a HT format, which is important when dealing with precious small samples. In addition to being able to handle small cardiomyocyte samples, these streamlined and semi-automated processes enable quick mechanistic analysis.

Integrated microfluidic system for isolating exosome and analyzing protein marker PD-L1

Exosomes are lipid-bilayered nanovesicles secreted by cells to mediate intercellular communication. Various kinds of biomolecules involved in exosomes offer non-invasive approaches for detecting or monitoring disease and developing targeted therapeutics. Here, we present an integrated microfluidic exosome isolation and detection system (EXID system) to analyze the abundance of the exosomal PD-L1 protein marker, which is a transmembrane protein expressed by tumors to suppress immune activation of T cells. By incorporating exosome isolation and biomarker labelling and quantification within a single microfluidic chip, our system reduced the total analysis time below 2 h. Using the EXID system, 7 categories of cell lines including cancer cell lines and control samples were profiled, where significant differences in the fluorescence intensity were observed with the limit of detection (LOD) down to 10.76 per microliter. Such noticeable variations in PD-L1 abundance among cancer cell lines highlighted the need of personalized treatments. Furthermore, 16 clinical samples from 7 post-treated cancer patients, 3 prior-treatment patients and 6 healthy controls, are tested, among which differences in sensitivity toward immune response were subsistent. Because the abundance of PD-L1 reflects the sensibility for immune response, our results provide useful guides to design immunotherapy strategies for different types of tumors.

Integration and Quantitative Visualization of 3,3',5,5'-Tetramethylbenzidine-Probed Enzyme-Linked Immunosorbent Assay-like Signals in a Photothermal Bar-Chart Microfluidic Chip for Multiplexed Immunosensing

The photothermal effect shows significant promise for various biomedical applications but is rarely exploited for microfluidic lab-on-a-chip bioassays. Herein, a photothermal bar-chart microfluidic immunosensing chip, with the integration of the conventional 3,3',5,5'-tetramethylbenzidine (TMB)-probed enzyme-linked immunosorbent assay (ELISA)-like system, was developed based on exploiting the photothermal pumping technique for visual bar-chart microfluidic immunosensing. Both the sandwich ELISA-like system and the photothermal pumping protocol were integrated into a single photothermal bar-chart chip. On-chip immunocaptured iron oxide nanoparticles catalyzed the oxidation of the chromogenic substrate, TMB, to produce a sensitive photothermal and chromogenic dual-functional probe, oxidized TMB. As the result of heat generation and the subsequent production of elevating vapor pressure in the sealed microfluidic environment, the on-chip near-infrared laser-driven photothermal effect of the probe served as a dose-dependent pumping force to drive the multiplexed quantitative display of the immunosensing signals as visual dye bar charts. Prostate-specific antigen as a model analyte was tested at a limit of detection of 1.9 ng·mL^-1, lower than the clinical diagnostic threshold of prostate cancer. This work presents a new perspective for microfluidic integration and multiplexed quantitative bar-chart visualization of the conventional TMB-probed ELISA signals possibly by means of an affordable handheld laser pointer in a lab-on-a-chip format.

Point-of-Care Testing for Multiple Cardiac Markers Based on a Snail-Shaped Microfluidic Chip

Existing methods for detecting cardiac markers are difficult to be applied in point-of-care testing (POCT) due to complex operation, long time consumption, and low sensitivity. Here, we report a snail-shaped microfluidic chip (SMC) for the multiplex detection of cTnI, CK-MB, and Myo with high sensitivity and a short detection time. The SMC consists of a sandwich structure: a channel layer with a mixer and reaction zone, a reaction layer coated with capture antibodies, and a base layer. The opening or closing of the microchannels is realized by controlling the downward movement of the press-type mechanical valve. The chemiluminescence method was used as a signal readout, and the experimental conditions were optimized. SMC could detect cTnI, CK-MB, and Myo at concentrations as low as 1.02, 1.37, and 4.15. The SMC will be a promising platform for a simultaneous determination of multianalytes and shows a potential application in POCT.

A quantum dot microspheres-based highly specific and sensitive three-dimensional microarray for multiplexed detection of inflammatory factors

The development trend ofin vitrodiagnostics is to obtain various biological information from a sample at extremely low concentration and volume, which has promoted its progress in accurate and sensitive multiplexed detection. Here, we developed a single color quantum dot (QD) based three-dimensional (3D) structure matrix microarray and conducted the detection of two inflammatory factors (C-reactive protein (CRP) and serum amyloid A (SAA)) by a self-built fluorescence detection system. This strategy increased detection sensitivity by immobilizing the antibody specifically on the 3D substrate because it captured more than about 7 times of 'effective' antibodies compared to the two-dimensional (2D) plane. Compared to the dual QDs-2D fluorescence-linked immunosorbent assay, the limit of detection (LOD) of 3D microarray based on QDs modified with amphiphilic polymers has been further improved to 0.11 ng ml^-1for SAA assay and to 0.16 ng ml^-1for CRP assay, respectively. By using QD microspheres (SiO₂@QDs@SiO₂-COOH, containing approximately 200-300 hydrophobic QDs on per SiO₂sphere) as fluorescent labels, the LOD for CRP and SAA of 3D microarray reached as high as 15 pg ml^-1and 86 pg ml^-1, and the sensitivity was further improved by 28-fold and 425-fold, respectively. Because of its excellent performance, this QD microspheres-based 3D microarray has great application potential for highly sensitive and multiplexed quantitative detection of other biomarkers, small molecules, and antibiotic residues in biomedicine and food safety.

Toward Development of a Label-Free Detection Technique for Microfluidic Fluorometric Peptide-Based Biosensor Systems

The problems of chronic or noncommunicable diseases (NCD) that now kill around 40 million people each year require multiparametric combinatorial diagnostics for the selection of effective treatment tactics. This could be implemented using the biosensor principle based on peptide aptamers for spatial recognition of corresponding protein markers of diseases in biological fluids. In this paper, a low-cost label-free principle of biomarker detection using a biosensor system based on fluorometric registration of the target proteins bound to peptide aptamers was investigated. The main detection principle considered includes the re-emission of the natural fluorescence of selectively bound protein markers into a longer-wavelength radiation easily detectable by common charge-coupled devices (CCD) using a specific luminophore. Implementation of this type of detection system demands the reduction of all types of stray light and background fluorescence of construction materials and aptamers. The latter was achieved by careful selection of materials and design of peptide aptamers with substituted aromatic amino acid residues and considering troponin T, troponin I, and bovine serum albumin as an example. The peptide aptamers for troponin T were designed in silico using the «Protein 3D» (SPB ETU, St. Petersburg, Russia) software. The luminophore was selected from the line of ZnS-based solid-state compounds. The test microfluidic system was arranged as a flow through a massive of four working chambers for immobilization of peptide aptamers, coupled with the optical detection system, based on thick film technology. The planar optical setup of the biosensor registration system was arranged as an excitation-emission cascade including 280 nm ultraviolet (UV) light-emitting diode (LED), polypropylene (PP) UV transparent film, proteins layer, glass filter, luminophore layer, and CCD sensor. A laboratory sample has been created.

A Portable Microfluidic System for Point-of-Care Detection of Multiple Protein Biomarkers

Protein biomarkers are indicators of many diseases and are commonly used for disease diagnosis and prognosis prediction in the clinic. The urgent need for point-of-care (POC) detection of protein biomarkers has promoted the development of automated and fully sealed immunoassay platforms. In this study, a portable microfluidic system was established for the POC detection of multiple protein biomarkers by combining a protein microarray for a multiplex immunoassay and a microfluidic cassette for reagent storage and liquid manipulation. The entire procedure for the immunoassay was automatically conducted, which included the antibody–antigen reaction, washing and detection. Alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA) and carcinoma antigen 125 (CA125) were simultaneously detected in this system within 40 min with limits of detection of 0.303 ng/mL, 1.870 ng/mL, and 18.617 U/mL, respectively. Five clinical samples were collected and tested, and the results show good correlations compared to those measured by the commercial instrument in the hospital. The immunoassay cassette system can function as a versatile platform for the rapid and sensitive multiplexed detection of biomarkers; therefore, it has great potential for POC diagnostics.

Applications of microcapillary films in bioanalytical techniques

Microcapillary film (MCF) is an extruded plastic film with an array of parallel microcapillaries (30-500 μm) and it has wide potential applications in bioanalytical techniques as a microfluidic platform. With different surface modification strategies, an MCF combines the advantages of its structure and modified chemical properties to realize various bioanalytical functions. In this review, we begin by introducing the manufacturing process of MCFs, common materials used to produce MCFs, surface treatment approaches of inner surfaces, and a signal detection and readout system of the MCF platform. Then, we summarize some typical applications of MCFs, particularly in protein chromatography, Escherichia coli detection for urinary tract infections, prostate-specific antigen detection for prostate cancer and multiplex immunoassays. Finally, future perspectives of MCFs in bioanalytical techniques are discussed.

3D printed smart silk wearable sensors

Wearable sensors play a key role in point-of-care testing (POCT) for their flexible and integration capability for sensitive physiological and biochemical sensing. Here, we present a multifunction wearable silk patch with both electronic channels and microchannels by utilizing matrix-assisted sacrificial 3D printing methods. Owing to the unique properties of a composite silk film (polyvinyl alcohol (PVA) and silk fibroin (SF)), the wearable sensors possess excellent tensile properties, self-healing ability and biocompatibility. Multi-layer channel (microfluidics and microcircuit)-integrated silk wearable sensors were then fabricated for simultaneous sensitive sensing of human cancer markers (carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP)) and motion monitoring. These features of the silk wearable sensors indicate their potential value for sensitive sensing, which will enable them to find broader applications in many fields in POCT, artificial skin and organ-on-a-chip systems.

Siphon-Controlled Automation on a Lab-on-a-Disc Using Event-Triggered Dissolvable Film Valves

Within microfluidic technologies, the centrifugal microfluidic “Lab-on-a-Disc” (LoaD) platform offers great potential for use at the PoC and in low-resource settings due to its robustness and the ability to port and miniaturize ‘wet bench’ laboratory protocols. We present the combination of ‘event-triggered dissolvable film valves’ with a centrifugo-pneumatic siphon structure to enable control and timing, through changes in disc spin-speed, of the release and incubations of eight samples/reagents/wash buffers. Based on these microfluidic techniques, we integrated and automated a chemiluminescent immunoassay for detection of the CVD risk factor marker C-reactive protein displaying a limit of detection (LOD) of 44.87 ng mL⁻¹ and limit of quantitation (LoQ) of 135.87 ng mL⁻¹.

Rapid highly sensitive general protein quantification through on-chip chemiluminescence

Protein detection and quantification is a routinely performed procedure in research laboratories, predominantly executed either by spectroscopy-based measurements, such as NanoDrop, or by colorimetric assays. The detection limits of such assays, however, are limited to μ M concentrations. To establish an approach that achieves general protein detection at an enhanced sensitivity and without necessitating the requirement for signal amplification steps or a multicomponent detection system, here, we established a chemiluminescence-based protein detection assay. Our assay specifically targeted primary amines in proteins, which permitted characterization of any protein sample and, moreover, its latent nature eliminated the requirement for washing steps providing a simple route to implementation. Additionally, the use of a chemiluminescence-based readout ensured that the assay could be operated in an excitation source-free manner, which did not only permit an enhanced sensitivity due to a reduced background signal but also allowed for the use of a very simple optical setup comprising only an objective and a detection element. Using this assay, we demonstrated quantitative protein detection over a concentration range of five orders of magnitude and down to a high sensitivity of 10 pg mL - 1 , corresponding to pM concentrations. The capability of the platform presented here to achieve a high detection sensitivity without the requirement for a multistep operation or a multicomponent optical system sets the basis for a simple yet universal and sensitive protein detection strategy.

A flux-adaptable pump-free microfluidics-based self-contained platform for multiplex cancer biomarker detection

Microfluidics drives technological advancement in point-of-care (POC) bioanalytical diagnostics towards portability, fast response and low cost. In most microfluidic bioanalytical applications, flowing antigen/antibody reacts with immobilized antibody/antigen at a constant flux; it is difficult to reach a compromise to simultaneously realize sufficient time for the antigen-antibody interaction and short time for the entire assay. Here, we present a pump-free microfluidic chip, in which flow is self-initialized by capillary pumping and continued by imbibition of a filter paper. Microfluidic units in teardrop shape ensure that flow passes through the reaction areas at a reduced flux to facilitate the association between antigen and antibody and speeds up after the reaction areas. By spotting different antibodies into the reaction area, four types of biomarkers can be measured simultaneously in one microfluidic chip. Moreover, a small-sized instrument was developed for chemiluminescence detection and signal analysis. The system was validated by testing four biomarkers of colorectal cancer using plasma samples from patients. The assay took about 20 minutes. The limit of detection is 0.89 ng mL^-1, 1.72 ng mL^-1, 3.62 U mL^-1 and 1.05 U mL^-1 for the assays of carcinoembryonic antigen, alpha-fetoprotein, carbohydrate antigen 125 and carbohydrate antigen 19-9, respectively. This flux-adaptable and self-contained microfluidic platform is expected to be useful in various POC disease-monitoring applications.

Recent Trends in Nanomaterial-Based Biosensors for Point-of-Care Testing

In recent years, nanomaterials of different shape, size, and composition have been prepared and characterized, such as gold and silver nanoparticles, quantum dots, mesoporous silica nanoparticles, carbon nanomaterials, and hybrid nanocomposites. Because of their unique physical and chemical properties, these nanomaterials are increasingly used in point-of-care testing (POCT) to improve analytical performance and simplify detection process. They are used either as carriers for immobilizing biorecognition elements, or as labels for signal generation, transduction and amplification. In this commentary, we highlight recent POCT technologies that employ nanotechnology for the analysis of disease biomarkers, including small-molecule metabolites, enzymes, proteins, nucleic acids, cancer cells, and pathogens. Recent advances in lateral flow tests, printable electrochemical biosensors, and microfluidics-based devices are summarized. Existing challenges and future directions are also discussed.

Multiplexed tri-mode visual outputs of immunoassay signals on a clip-magazine-assembled photothermal biosensing disk

The photothermal biosensing principle is of increasing interest for point-of-care detection, but has rarely been applied in portable analytical devices in a lab-on-a-chip format. Herein, a photothermally responsive poly (methyl methacrylate) (PMMA)/paper hybrid disk (PT-Disk) was developed as a novel photothermal immunoassay device with the integration of a clip-magazine-assembled photothermal biosensing strategy. The PT-Disk consisted of a dissociative thermoresponsive hydrogel-loaded clip unit where the sandwich-type immunoreaction with an iron oxide-to-Prussian blue nanoparticle (PB NP) conversion took place and a magazine bearer for the rotational clip assembly and visual signal outputs. Upon laser irradiation of the clip-magazine-assembled PT-Disk, on-chip photothermal effect of PB NPs triggered both dose-dependent temperature elevation and the subsequent release of dye solutions from the central clip unit to surrounding magazine-bearing paper channels as the result of phase transition of the hydrogels, realizing multiplexed thermal image- and distance-based visual quantitative signal outputs in combination with the preliminary colorimetric readout on the PT-Disk. Using the multiplexed tri-mode signal outputs, the PT-Disk can quantify prostate specific antigen with limits of detection of 1.4-2.8 ng mL^-1. This is the first attempt to apply the photothermal biosensing principle in portable PMMA/paper-based analytical devices, which offers not only versatile on-chip visual quantitative signal outputs, but also the implementation of the photothermal biosensing principle in a lab-on-a-chip format.

Washing-free centrifugal microchip fluorescence immunoassay for rapid and point-of-care detection of protein

Simplifying the procedure of immunoassay is still a challenge due to problems such as multiple washing processes, complicated chemical modification and expensive cost. In this study, we developed a portable centrifugal microchip fluorescence immunoassay for washing-free, rapid, quantitative and point-of-care (POC) detection of protein. The designed microchip was fabricated by polycarbonate and assembled by double-sided adhesive tape using injecting molding with high scalability and low cost. The centrifugal strategy is capable of washing-out the bio-fluid and improving signal-to-noise ratio. Matrix nano-spotting method was employed to facilitate satisfactory immunological binding sites with the advantage of high capture efficiency and reproducibility. The proposed approach was capable of sensitively detecting procalcitonin (PCT) with a wide dynamic ranging from 0.10 ng/mL to 70.00 ng/mL within 10 min. Furthermore, this novel integrated diagnostic tool was successfully applied to detect PCT in 101 clinical samples with good consistency with Roche's method, indicating its attractive practical application capability. With favorable simplicity, rapidity, low cost and excellent analytical performance, our method holds great promise for POC diagnostics of proteins.

Towards practical sample preparation in point-of-care testing: user-friendly microfluidic devices

Microfluidic technologies offer a number of advantages for sample preparation in point-of-care testing (POCT), but the requirement for complicated external pumping systems limits their wide use. To facilitate sample preparation in POCT, various methods have been developed to operate microfluidic devices without complicated external pumping systems. In this review, we introduce an overview of user-friendly microfluidic devices for practical sample preparation in POCT, including self- and hand-operated microfluidic devices. Self-operated microfluidic devices exploit capillary force, vacuum-driven pressure, or gas-generating chemical reactions to apply pressure into microchannels, and hand-operated microfluidic devices utilize human power sources using simple equipment, including a syringe, pipette, or simply by using finger actuation. Furthermore, this review provides future perspectives to realize user-friendly integrated microfluidic circuits for wider applications with the integration of simple microfluidic valves.

Integrated Single Microbead-Arrayed μ-Fluidic Platform for the Automated Detection of Multiplexed Biomarkers

An automated, single microbead-arrayed μ-fluidic immunoassay (AMIA) device is innovatively devised in this study, which enables the highly sensitive and simultaneous detection of multiplex biomarkers with fully automatic operations. The AMIA platform not only achieves automated assay processing and multiplexed target detection by integrating single microbead manipulation, sample loading, multistep washing, and immunoreaction on a microfluidic chip but also confers high sensitivity due to the highly efficient signal enriching effect on a single microbead by the use of only a routine sandwich immunoreaction. As such, as low as the pg/mL level of multiplexed protein biomarkers can be simultaneously determined in a quite small volume of serum (∼20 μL is enough), which can well meet the clinical demand for disease screening and prognosis. What is more, the detection results of several clinically important biomarkers in clinical samples with the AMIA platform exhibit excellent consistency with those obtained by using a standard clinical test. Thus, in virtue of the excellent features in terms of high sensitivity, multiplexing capability, generality, and high degree of automation, the AMIA provides a practical and user-friendly platform for assaying different biomarkers in clinical diagnostics and point-of-care testing.

Improving the limit of detection in portable luminescent assay readers through smart optical design

Critical biomarkers of disease are increasingly being detected by point-of-care assays. Chemiluminescence (CL) and electrochemiluminescence (ECL) are often used in such assays due to their convenience and that they do not require light sources or other components that could complicate or add cost to the system. Reports of these assays often include readers built on a cellphone platform or constructed from low-cost components. However, the impact the optical design has on the limit of detection (LOD) in these systems remains unexamined. Here, we report a theoretical rubric to evaluate different optical designs in terms of maximizing the use of photons emitted from a CL or ECL assay to improve the LOD. We demonstrate that the majority of cellphone designs reported in the literature are not optimized, in part due to misunderstandings of the optical tradeoffs in collection systems, and in part due to limitations imposed on the designs arising from the use of a mobile phone with a very small lens aperture. Based on the theoretical rubric, we design a new portable reader built using off-the-shelf condenser optics, and demonstrate a nearly 10× performance enhancement compared to prior reports on an ECL assays running on a portable chip.

Integrated microfluidic pumps and valves operated by finger actuation

Here, we report an integrated operation of microfluidic pumps and valves only by finger actuation. As the working principle of the finger-actuated microfluidic pumps includes deflection of the poly(dimethylsiloxane) (PDMS) membrane, the pneumatic valves for controlling the flow direction can be easily integrated with the pumps. Using a single button, the flow path can be determined and flow generation can be achieved. We also verified the integrated operation of finger-actuated pumps and valves by demonstrating nucleic acid purification.

Hierarchically structured microchip for point-of-care immunoassays with dynamic detection ranges

Point-of-care (POC) medical assays provide critical information to guide clinical therapy for a broad range of medical scenarios, such as resource-poor settings and specialty departments in hospitals. Even though many types of POC assays can be done in automated devices, these POC assays typically cannot well accommodate the multiplexed detection of biomarkers where a large dynamic range is needed. Here, we report a POC assay, which is both automated and suitable for detecting multiple biomarkers with dynamic detection ranges. We call it a dynamic multiplexed immunoassay (DMI). We control the concentrations of capture antibodies and the intensity of the readout signal to dynamically modulate the detection range of immunoassays (pg mL^-1 to μg mL^-1), leading to the multiplexed detection of C-reactive protein (CRP), procalcitonin (PCT), and interleukin 6 (IL-6) simultaneously in undiluted human serum samples. The POC assay allows the rapid and accurate detection of infection in patients.

An open-space microfluidic chip with fluid walls for online detection of VEGF via rolling circle amplification

We report an open-space microfluidic chip with fluid walls, integrating functions of cell culture and online detection of secreted proteins controlled by the interfacial tension value.

Despite traditional poly-dimethyl siloxane (PDMS) microfluidic devices having great potential in various biological studies, they are limited by sophisticated fabrication processes and low utilization. An easily controlled microfluidic platform with high efficiency and low cost is desperately required. In this work, we present an open-space microfluidic chip with fluid walls, integrating cell culture and online semi-quantitative detection of vascular endothelial growth factor (VEGF) via rolling circle amplification (RCA) reaction. In comparison with conventional co-culture detecting platforms, this method features the prominent advantages of saving reagents and time, a simplified chip fabrication process, and avoiding additional assistance for online detection with the help of an interfacial tension valve. On such a multi-functional microfluidic chip, cells (human umbilical vein endothelial cells and malignant glioma cells) could maintain regular growth and cell viability. VEGF could be detected with excellent specificity and good linearity in the range of 10–250 pg mL^–1. Meanwhile, VEGF secreted by malignant glioma cells was also detected online and obviously increased when cells were stimulated by deferoxamine (DFO) to mimic a hypoxic microenvironment. The designed biochip with fluid walls provides a new perspective for micro-total analysis and could be promisingly applied in future clinical diagnosis and drug analysis.

Rapid Isolation and Multiplexed Detection of Exosome Tumor Markers Via Queued Beads Combined with Quantum Dots in a Microarray

Tumor-derived exosomes are actively involved in cancer progression and metastasis and have emerged as a promising marker for cancer diagnosis in liquid biopsy. Because of their nanoscale size, complex biogenesis, and methodological limitations related to exosome isolation and detection, advancements in their analysis remain slow. Microfluidic technology offers a better analytic approach compared with conventional methods. Here, we developed a bead-based microarray for exosome isolation and multiplexed tumor marker detection. Using this method, exosomes are isolated by binding to antibodies on the bead surface, and tumor markers on the exosomes are detected through quantum dot (QD) probes. The beads are then uniformly trapped and queued among micropillars in the chip. This design benefits fluorescence observation by dispersing the signals into every single bead, thereby avoiding optical interference and enabling more accurate test results. We analyzed exosomes in the cell culture supernatant of lung cancer and endothelial cell lines, and different lung cancer markers labeled with three QD probes were used to conduct multiplexed detection of exosome surface protein markers. Lung cancer-derived samples showed much higher (~ sixfold-tenfold) fluorescence intensity than endothelial cell samples, and different types of lung cancer samples showed distinctive marker expression levels. Additionally, using the chip to detect clinical plasma samples from cancer patients showed good diagnostic power and revealed a well consistency with conventional tests for serological markers. These results provide insight into a promising method for exosome tumor marker detection and early-stage cancer diagnosis.