Integrated lab-on-chip biosensing systems based on magnetic particle actuation--a comprehensive review

Combined Funnel, Concentrator, and Particle Valve Functional Element for Magnetophoretic Bead Transport Based on Engineered Magnetic Domain Patterns

Controlled actuation of superparamagnetic beads (SPBs) within a microfluidic environment using tailored dynamic magnetic field landscapes (MFLs) is a potent approach for the realization of point-of-care diagnostics within Lab-on-a-chip (LOC) systems. Making use of an engineered magnetic domain pattern as the MFL source, a functional LOC-element with combined magnetophoretic "funnel", concentrator, and "valve" functions for micron-sized SPBs is presented. A parallel-stripe domain pattern design with periodically decreasing/increasing stripe lengths is fabricated in a topographically flat continuous exchange biased (EB) thin film system by ion bombardment induced magnetic patterning (IBMP). It is demonstrated that, upon application of external magnetic field pulses, a fully reversible concentration of SPBs at the domain pattern's focal point occurs. In addition, it is shown that this functionality may be used as an SPB "funnel", allowing only a maximum number of particles to pass through the focal point. Adjusting the pulse time length, the focal point can be clogged up for incoming SPBs, resembling an on/off switchable particle "valve". The observations are supported by quantitative theoretical force considerations.

Magnetic nanoparticles fabricated/integrated with microfluidics for biological applications: A review

Nanostructured materials have gained significant attention in recent years for their potential in biological applications, such as cell and biomolecular sorting, as well as early detection of metastatic cancer. Among these materials, magnetic nanoparticles (MNPs) stand out for their easy functionalization, high specific surface area, chemical stability, and superparamagnetic properties. However, conventional fabrication methods can lead to inconsistencies in MNPs' characteristics and performance, highlighting the need for a cost-effective, controllable, and reproducible synthesis approach. In this review, we will discuss the utilization of microfluidic technology as a cutting-edge strategy for the continuous and regulated synthesis of MNPs. This approach has proven effective in producing MNPs with a superior biomedical performance by offering precise control over particle size, shape, and surface properties. We will examine the latest research findings on developing and integrating MNPs synthesized through continuous microfluidic processes for a wide range of biological applications. By providing an overview of the current state of the field, this review aims to showcase the advantages of microfluidics in the fabrication and integration of MNPs, emphasizing their potential to revolutionize diagnostic and therapeutic methods within the realm of biotechnology.

On-Particle Hyperbranched Rolling Circle Amplification-Scaffolded Magnetic Nanoactuator Assembly for Ferromagnetic Resonance Detection of MicroRNA

Inspired by natural molecular machines, scientists are devoted to designing nanomachines that can navigate in aqueous solutions, sense their microenvironment, actuate, and respond. Among different strategies, magnetically driven nanoactuators can easily be operated remotely in liquids and thus are valuable in biosensing. Here we report a magnetic nanoactuator swarm with rotating-magnetic-field-controlled conformational changes for reaction acceleration and target quantification. By grafting nucleic acid amplification primers, magnetic nanoparticle (MNP) actuators can assemble and be fixed with a flexible DNA scaffold generated by surface-localized hyperbranched rolling circle amplification in response to the presence of a target microRNA, osa-miR156. Net magnetic anisotropy changes of the system induced by the MNP assembly can be measured by ferromagnetic resonance spectroscopy as shifts in the resonance field. With a total assay time of ca. 120 min, the proposed biosensor offers a limit of detection of 6 fM with a dynamic detection range spanning 5 orders of magnitude. The specificity of the system is validated by testing different microRNAs and salmon sperm DNA. Endogenous microRNAs extracted from Oryza sativa leaves are tested with both quantitative reverse transcription-PCR and our approach, showing comparable performances with a Pearson correlation coefficient >0.9 (n = 20).

Regulating Biomolecular Surface Interactions Using Tunable Acoustic Streaming

Diffusion limitations and nonspecific surface absorption are great challenges for developing micro-/nanoscale affinity biosensors. There are very limited approaches that can solve these issues at the same time. Here, an acoustic streaming approach enabled by a gigahertz (GHz) resonator is presented to promote mass transfer of analytes through the jet mode and biofouling removal through the shear mode, which can be switched by tuning the deviation angle, α, between the resonator and the sensor. Simulations show that the jet mode (α ≤ 0) drives the analytes in the fluid toward the sensing surface, overcomes the diffusion limitation, and enhances the binding; while the shear mode (0 < α < π/4) provides a scouring action to remove the biofouling from the sensor. Experimental studies were performed by integrating this GHz resonator with optoelectronic sensing systems, where a 34-fold enhancement for the initial binding rate was obtained. Featuring high efficiency, controllability, and versatility, we believe that this GHz acoustic streaming approach holds promise for many kinds of biosensing systems as well as lab-on-chip systems.

Improving Pathways to Care for Patients at High Psychosis Risk in Switzerland: PsyYoung Study Protocol

AIMS

Psychotic disorders are one of the main causes of chronic disability in young people. An at-risk mental state (ARMS) is represented by subclinical symptoms that precede the first episode of psychosis (FEP). The PsyYoung project aims to optimize the detection of an ARMS while reducing unnecessary psychiatric treatments. It investigates the effects of service changes on the referrals and outcomes of young people with ARMS or a FEP.

METHODS

Six psychiatric outpatient clinics in three cantons (Basel-Stadt, Vaud, and Geneva) participated in the project. They passed through an implementation phase including service changes and the adaptation of a standardized stepped care model for diagnosis and assessment, in addition to measures for increasing the awareness, networking and training of local professionals.

PRELIMINARY RESULTS

All participating cantons had entered the implementation phase. By March 2023, there were 619 referrals to participating sites. A total of 163 patients (37% FEP and 31% ARMS) and 15 close relatives had participated in individual longitudinal assessments, and 26 patients participated in qualitative interviews.

CONCLUSION

This national collaborative project addresses the issue of early intervention for emerging psychoses, and creates spaces for fruitful reflections and collaboration in Switzerland. The ultimate aim of PsyYoung is to harmonize clinical practices in early intervention of psychosis on a national level.

Topological Metamaterials

The topological properties of an object, associated with an integer called the topological invariant, are global features that cannot change continuously but only through abrupt variations, hence granting them intrinsic robustness. Engineered metamaterials (MMs) can be tailored to support highly nontrivial topological properties of their band structure, relative to their electronic, electromagnetic, acoustic and mechanical response, representing one of the major breakthroughs in physics over the past decade. Here, we review the foundations and the latest advances of topological photonic and phononic MMs, whose nontrivial wave interactions have become of great interest to a broad range of science disciplines, such as classical and quantum chemistry. We first introduce the basic concepts, including the notion of topological charge and geometric phase. We then discuss the topology of natural electronic materials, before reviewing their photonic/phononic topological MM analogues, including 2D topological MMs with and without time-reversal symmetry, Floquet topological insulators, 3D, higher-order, non-Hermitian and nonlinear topological MMs. We also discuss the topological aspects of scattering anomalies, chemical reactions and polaritons. This work aims at connecting the recent advances of topological concepts throughout a broad range of scientific areas and it highlights opportunities offered by topological MMs for the chemistry community and beyond.

Electrochemical magneto-immunoassay for detection of zika virus antibody in human serum

Zika virus (ZIKV) is a flavivirus transmitted by infected Aedes genus mosquitoes. An infected person may be asymptomatic or present symptoms such as fever, arthralgia, and in pregnancy it may lead to neurological disorders in the fetus, such as microcephaly. Based on the high dissemination potential of ZIVK and its similar antigen composition to other arboviruses, new approaches for selective virus detection are urgently needed. This work reports the development of an electrochemical immunoassay for detection of anti-ZIKV antibodies, using magnetic beads functionalized with recombinant protein derived from the non-structural protein 1 (ΔNS1-ZIKV) and anti-IgG antibodies labeled with horseradish peroxidase (HRP) enzyme. The magneto-immunoassay uses disposable microfluidic devices for detection of anti-ZIKV in serum samples. A linear response was obtained for a wide concentration range from 0.01 to 9.80 × 10⁵ pg mL^-1 (r² = 0.982), with a limit of detection of 0.48 pg mL^-1. The proposed immunoassay proved to be highly efficient for the detection of anti-ZIKV antibodies in serum, offering promising perspectives for the development of fast, simple, and affordable point-of-care diagnosis devices for ZIKV.

Magnetic Non-Spherical Particles Inducing Vortices in Microchannel for Effective Mixing

Mixing in microfluidic channels is dominated by diffusion owing to the absence of chaotic flow. However, high-efficiency microscale mixing over short distances is desired for the development of lab-on-chip systems. Here, enhanced mixing in microchannels achieved using magnetic nonspherical particles (MNSPs), is reported. Benefiting from the nonspherical shape of the MNSPs, secondary vortices exhibiting cyclical characteristics appear in microchannels when the MNSPs rotate under an external magnetic field. Increasing the rotation rate enlarges the secondary vortices, expanding the mixing zone and enhancing the mixing, resulting in a mixing efficiency exceeding 0.9 at Re of 0.069-0.69. Complementary micro-particle image velocimetry (µPIV) for flow field analysis clarifies the mixing mechanism. In addition, a chaotic vortex area is generated in the presence of two MNSPs, which shortens the distance required for achieving an appropriate mixing efficiency. This study demonstrates the potential of employing MNSPs as efficient mixers in lab-on-chip devices.

Design of Raman reporter-embedded magnetic/plasmonic hybrid nanostirrers for reliable microfluidic SERS biosensors

Magnetic-based microfluidic SERS biosensors hold great potential in various biological analyses due to their integrated advantages including easy manipulation, miniaturization and ultrasensitivity. However, it remains challenging to collect reliable SERS nanoprobe signals for quantitative analysis due to the irregular aggregation of magnetic carriers in a microfluidic chamber. Here, magnetic/plasmonic hybrid nanostirrers embedded with a Raman reporter are developed as capture carriers to improve the reliability of microfluidic SERS biosensors. Experimental results revealed that SERS signals from magnetic hybrid nanostirrers could serve as microenvironment beacons of their irregular aggregation, and a signal filtering method was proposed through exploring the relationship between the intensity range of beacons and the signal reproducibility of SERS nanoprobes using interleukin 6 as a model target analyte. Using the signal filtering method, reliable SERS nanoprobe signals with high reproducibility could be picked out from similar microenvironments according to their beacon intensity, and then the influence of irregular aggregation of magnetic carriers on the SERS nanoprobe could be eliminated. The filtered SERS nanoprobe signals also exhibited excellent repeatability from independent tests, which lay a solid foundation for a reliable working curve and subsequent accurate bioassay. This study provides a simple but promising route for reliable microfluidic SERS biosensors, which will further promote their practical application in biological analysis.

Versatile magnetic configuration for the control and manipulation of superparamagnetic nanoparticles

The control and manipulation of superparamagnetic nanoparticles (SP-MNP) is a significant challenge and has become increasingly important in various fields, especially in biomedical research. Yet, most of applications rely on relatively large nanoparticles, 50 nm or higher, mainly due to the fact that the magnetic control of smaller MNPs is often hampered by the thermally induced Brownian motion. Here we present a magnetic device able to manipulate remotely in microfluidic environment SP-MNPs smaller than 10 nm. The device is based on a specifically tailored configuration of movable permanent magnets. The experiments performed in 500 µm capillary have shown the ability to concentrate the SP-MNPs into regions characterized by different shapes and sizes ranging from 100 to 200 µm. The results are explained by straightforward calculations and comparison between magnetic and thermal energies. We provide then a comprehensive description of the magnetic field intensity and its spatial distribution for the confinement and motion of magnetic nanoparticles for a wide range of sizes. We believe this description could be used to establish accurate and quantitative magnetic protocols not only for biomedical applications, but also for environment, food, security, and other areas.

Applications of magnetic and electromagnetic forces in micro-analytical systems

Novel applications of magnetic fields in analytical chemistry have become a remarkable trend in the last two decades. Various magnetic forces have been employed for the migration, orientation, manipulation, and trapping of microparticles, and new analytical platforms for separating and detecting molecules have been proposed. Magnetic materials such as functional magnetic nanoparticles, magnetic nanocomposites, and specially designed magnetic solids and liquids have also been developed for analytical purposes. Numerous attractive applications of magnetic and electromagnetic forces on magnetic and non-magnetic materials have been studied, but fundamental studies to understand the working principles of magnetic forces have been challenging. These studies will form a new field of magneto-analytical science, which should be developed as an interdisciplinary field. In this review, essential pioneering works and recent attractive developments are presented.

A modular microfluidic device that uses magnetically actuatable microposts for enhanced magnetic bead-based workflows

Magnetic beads have been widely and successfully used for target enrichment in life science assays. There exists a large variety of commercially available magnetic beads functionalized for specific target capture, as well as options that enable simple surface modifications for custom applications. While magnetic beads are ideal for use in the macrofluidic context of typical laboratory workflows, their performance drops in microfluidic contexts, such as consumables for point-of-care diagnostics. A primary cause is the diffusion-limited analyte transport in these low Reynolds number environments. A new method, BeadPak, uses magnetically actuatable microposts to enhance analyte transport, improving yield of the desired targets. Critical parameters were defined for the operation of this technology and its performance characterized in canonical life-science assays. BeadPak achieved up to 1000× faster capture than a microfluidic chamber relying on diffusion alone, enabled a significant specimen concentration via volume reduction, and demonstrated compatibility with a range of biological specimens. The results shown in this work can be extended to other systems that utilize magnetic beads for target capture, concentration, and/or purification.

Development of a Simple Fabrication Method for Magnetic Micro Stir Bars and Induction of Rotational Motion in Chlamydomonas reinhardtii

A magnetic micro stirrer bar (MMSB) is used in the mixing operation of microfluidic devices. We have established a low-cost and easy method to make MMSBs using magnetic (neodymium magnets, magnet sheets) or non-magnetic powders (SUS304) as materials. We demonstrated three kinds of MMSB have respective advantages. To confirm the practical use of this MMSB, a cell suspension of the motile unicellular green alga Chlamydomonas reinhardtii was stirred in microwells. As a result, the number of rotating cells increased with only one of the two flagella mechanically removed by the shear force of the rotating bar, which facilitates the kinetic analysis of the flagellar motion of the cell. The rotational motion of the monoflagellate cell was modeled as translational (orbital) + spinning motion of a sphere in a viscous fluid and the driving force per flagellum was confirmed to be consistent with previous literature. Since the present method does not use genetic manipulations or chemicals to remove a flagellum, it is possible to obtain cells in a more naturally viable state quickly and easily than before. However, since the components eluted from the powder material harm the health of cells, it was suggested that MMSB coated with resin for long-term use would be suitable for more diverse applications.

A self-contained acoustofluidic platform for biomarker detection

Self-contained microfluidic platforms with on-chip integration of flow control units, microreactors, (bio)sensors, etc. are ideal systems for point-of-care (POC) testing. However, current approaches such as micropumps and microvalves, increase the cost and the control system, and it is rather difficult to integrate into a single chip. Herein, we demonstrated a versatile acoustofluidic platform actuated by a Lamb wave resonator (LWR) array, in which pumping, mixing, fluidic switching, and particle trapping are all achieved on a single chip. The high-speed microscale acoustic streaming triggered by the LWR in the confined microchannel can be utilized to realize a flow resistor and switch. Variable unidirectional pumping was realized by regulating the relative position of the LWR in various custom-designed microfluidic structures and adoption of different geometric parameters for the microchannel. In addition, to realize quantitative biomarker detection, the on-chip flow resistor, micropump, micromixer and particle trapper were also integrated with a CMOS photo sensor and electronic driver circuit, resulting in an automated handheld microfluidic system with no moving parts. Finally, the acoustofluidic platform was tested for prostate-specific antigen (PSA) sensing, which demonstrates the biocompatibility and applied potency of this proposed self-contained system in POC biomedical applications.

Emerging trends in the nanomedicine applications of functionalized magnetic nanoparticles as novel therapies for acute and chronic diseases

High-quality point-of-care is critical for timely decision of disease diagnosis and healthcare management. In this regard, biosensors have revolutionized the field of rapid testing and screening, however, are confounded by several technical challenges including material cost, half-life, stability, site-specific targeting, analytes specificity, and detection sensitivity that affect the overall diagnostic potential and therapeutic profile. Despite their advances in point-of-care testing, very few classical biosensors have proven effective and commercially viable in situations of healthcare emergency including the recent COVID-19 pandemic. To overcome these challenges functionalized magnetic nanoparticles (MNPs) have emerged as key players in advancing the biomedical and healthcare sector with promising applications during the ongoing healthcare crises. This critical review focus on understanding recent developments in theranostic applications of functionalized magnetic nanoparticles (MNPs). Given the profound global economic and health burden, we discuss the therapeutic impact of functionalized MNPs in acute and chronic diseases like small RNA therapeutics, vascular diseases, neurological disorders, and cancer, as well as for COVID-19 testing. Lastly, we culminate with a futuristic perspective on the scope of this field and provide an insight into the emerging opportunities whose impact is anticipated to disrupt the healthcare industry.

A handheld 3D-printed microchip for simple integration of the H2O2-producing enzymatic reactions with subsequent chemiluminescence detection: Application for sugars

Herein, a novel lab-on-a-chip (LoC) device fabricated by 3D printing based on H₂O₂-producing enzymatic reactions with sensitive chemiluminescence (CL) detection was developed to measure different sugars, including glucose, fructose, sucrose, and maltose, in honey, juice, and rice flour samples. The pumpless microchip included two main parts, separated by new cone-shape blocking valves; part A for sample introduction and subsequent enzymatic reaction, besides the CL reagent (luminol) container, and part B for detection. The specific enzyme(s) were embedded into the pores of the zinc zeolite-imidazole framework (ZIF-8) to improve their storage stability. By opening the valves, H₂O₂ produced by enzymatic reaction and luminol could flow through the designed channels into the detection zone on part B, where a 2D cobalt-imidazole framework was embedded to improve the luminol-H₂O₂ CL emission. The obtained signal was proportional to the considered sugar concentration, with the detection limits range of 20-268 µM.

Optomagnetic biosensors: Volumetric sensing based on magnetic actuation-induced optical modulations

In comparison to alternative nanomaterials, magnetic micron/nano-sized particles show unique advantages, e.g., easy manipulation, stable signal, and high contrast. By applying magnetic actuation, magnetic particles exert forces on target objects for highly selective operation even in non-purified samples. We herein describe a subgroup of magnetic biosensors, namely optomagnetic biosensors, which employ alternating magnetic fields to generate periodic movements of magnetic labels. The optical modulation induced by the dynamics of magnetic labels is then analyzed by photodetectors, providing information of, e.g., hydrodynamic size changes of the magnetic labels. Optomagnetic sensing mechanisms can suppress the noise (by performing lock-in detection), accelerate the reaction (by magnetic force-enhanced molecular collision), and facilitate homogeneous/volumetric detection. Moreover, optomagnetic sensing can be performed using a low magnetic field (<10 mT) without sophisticated light sources or pickup coils, further enhancing its applicability for point-of-care tests. This review concentrates on optomagnetic biosensing techniques of different concepts classified by the magnetic actuation strategy, i.e., magnetic field-enhanced agglutination, rotating magnetic field-based particle rotation, and oscillating magnetic field-induced Brownian relaxation. Optomagnetic sensing principles applied with different actuation strategies are introduced as well. For each representative optomagnetic biosensor, a simple immunoassay strategy-based application is introduced (if possible) for methodological comparison. Thereafter, challenges and perspectives are discussed, including minimization of nonspecific binding, on-chip integration, and multiplex detection, all of which are key requirements in point-of-care diagnostics.

Active Opto-Magnetic Biosensing with Silicon Microring Resonators

Integrated optical biosensors are gaining increasing attention for their exploitation in lab-on-chip platforms. The standard detection method is based on the measurement of the shift of some optical quantity induced by the immobilization of target molecules at the surface of an integrated optical element upon biomolecular recognition. However, this requires the acquisition of said quantity over the whole hybridization process, which can take hours, during which any external perturbation (e.g., temperature and mechanical instability) can seriously affect the measurement and contribute to a sizeable percentage of invalid tests. Here, we present a different assay concept, named Opto-Magnetic biosensing, allowing us to optically measure off-line (i.e., post hybridization) tiny variations of the effective refractive index seen by microring resonators upon immobilization of magnetic nanoparticles labelling target molecules. Bound magnetic nanoparticles are driven in oscillation by an external AC magnetic field and the corresponding modulation of the microring transfer function, due to the effective refractive index dependence on the position of the particles above the ring, is recorded using a lock-in technique. For a model system of DNA biomolecular recognition we reached a lowest detected concentration on the order of 10 pm, and data analysis shows an expected effective refractive index variation limit of detection of 7.5×10-9 RIU, in a measurement time of just a few seconds.

Using small-angle scattering to guide functional magnetic nanoparticle design

Magnetic nanoparticles offer unique potential for various technological, biomedical, or environmental applications thanks to the size-, shape- and material-dependent tunability of their magnetic properties. To optimize particles for a specific application, it is crucial to interrelate their performance with their structural and magnetic properties. This review presents the advantages of small-angle X-ray and neutron scattering techniques for achieving a detailed multiscale characterization of magnetic nanoparticles and their ensembles in a mesoscopic size range from 1 to a few hundred nanometers with nanometer resolution. Both X-rays and neutrons allow the ensemble-averaged determination of structural properties, such as particle morphology or particle arrangement in multilayers and 3D assemblies. Additionally, the magnetic scattering contributions enable retrieving the internal magnetization profile of the nanoparticles as well as the inter-particle moment correlations caused by interactions within dense assemblies. Most measurements are used to determine the time-averaged ensemble properties, in addition advanced small-angle scattering techniques exist that allow accessing particle and spin dynamics on various timescales. In this review, we focus on conventional small-angle X-ray and neutron scattering (SAXS and SANS), X-ray and neutron reflectometry, gracing-incidence SAXS and SANS, X-ray resonant magnetic scattering, and neutron spin-echo spectroscopy techniques. For each technique, we provide a general overview, present the latest scientific results, and discuss its strengths as well as sample requirements. Finally, we give our perspectives on how future small-angle scattering experiments, especially in combination with micromagnetic simulations, could help to optimize the performance of magnetic nanoparticles for specific applications.

Lab-on-a-Chip Devices for Point-of-Care Medical Diagnostics

The recent coronavirus (COVID-19) pandemic has underscored the need to move from traditional lab-centralized diagnostics to point-of-care (PoC) settings. Lab-on-a-chip (LoC) platforms facilitate the translation to PoC settings via the miniaturization, portability, integration, and automation of multiple assay functions onto a single chip. For this purpose, paper-based assays and microfluidic platforms are currently being extensively studied, and much focus is being directed towards simplifying their design while simultaneously improving multiplexing and automation capabilities. Signal amplification strategies are being applied to improve the performance of assays with respect to both sensitivity and selectivity, while smartphones are being integrated to expand the analytical power of the technology and promote its accessibility. In this chapter, we review the main technologies in the field of LoC platforms for PoC medical diagnostics and survey recent approaches for improving these assays.

Pipette-Tip-Enabled Digital Nucleic Acid Analyzer for COVID-19 Testing with Isothermal Amplification

Herein, a pipette-tip-enabled digital nucleic acid analyzer for high-performance COVID-19 testing is demonstrated. This is achieved by digital loop-mediated isothermal amplification (digital LAMP or dLAMP) using common laboratory equipment and materials. It is shown that simply fixing a glass capillary inside conventional pipette tips enables the generation of monodisperse, water-in-oil microdroplets with benchtop centrifugation. It is shown that using LAMP, the ORF1a/b gene, a standard test region for COVID-19 screening, can be amplified without a thermal cycler. The amplification allows counting of fluorescent microdroplets so that Poisson analysis can be performed to allow quantification with a limit of detection that is 1 order of magnitude better than those of nondigital techniques and comparable to those of commercial dLAMP platforms. It is envisioned that this work will inspire studies on ultrasensitive digital nucleic acid analyzers demanding both sensitivity and accessibility, which is pivotal to their large-scale applications.

Research on magnetic bead motion characteristics based on magnetic beads preset technology

In order to improve the detection efficiency and accuracy of microfluidic chip, a magnetic beads preset technology were designed by using double permanent magnets as external magnetic field and the motion characteristics of preset magnetic beads were studied. The control principle of magnetic beads preset technology was introduced in detail, and the control structure was designed. The coupled field characteristics for magnetic beads in microchannels were analyzed, and the motion models of magnetic beads were established based on the magnetic beads preset technology, including capture motion and mixing motion. The relationship between the magnetic field force and the flow velocity for capturing magnetic bead, and the mixing time under the influence of flow field and magnetic field were derived. The magnetic beads preset technology effect was verified by experiments and numerical simulations were developed to analyze the influence of aspect ratio of permanent magnet on magnetic field. The study showed that the accuracy and efficiency of the magnetic bead control in the microchannel could be better realized by the magnetic beads preset technology. The derivation of the magnetic bead motion model can understand the motion characteristics of the magnetic bead more clearly, facilitate accurate control of the magnetic bead, and improve the success rate of the microfluidic detection.

Ultrasonic Particle Manipulation in Glass Capillaries: A Concise Review

Ultrasonic particle manipulation (UPM), a non-contact and label-free method that uses ultrasonic waves to manipulate micro- or nano-scale particles, has recently gained significant attention in the microfluidics community. Moreover, glass is optically transparent and has dimensional stability, distinct acoustic impedance to water and a high acoustic quality factor, making it an excellent material for constructing chambers for ultrasonic resonators. Over the past several decades, glass capillaries are increasingly designed for a variety of UPMs, e.g., patterning, focusing, trapping and transporting of micron or submicron particles. Herein, we review established and emerging glass capillary-transducer devices, describing their underlying mechanisms of operation, with special emphasis on the application of glass capillaries with fluid channels of various cross-sections (i.e., rectangular, square and circular) on UPM. We believe that this review will provide a superior guidance for the design of glass capillary-based UPM devices for acoustic tweezers-based research.

Enhanced Microfluidic Sample Homogeneity and Improved Antibody-Based Assay Kinetics Due to Magnetic Mixing

Recent global events have distinctly demonstrated the need for fast diagnostic analysis of targets in a liquid sample. However, microfluidic lab-on-a-chip devices for point-of-care diagnostics can suffer from slow analysis due to poor mixing. Here, we experimentally explore the mixing effect within a microfluidic chamber, as obtained from superparamagnetic beads exposed to an out-of-plane (vertical) rotating magnetic field. Various magnetic protocols are explored, and the level of sample homogeneity is measured by determining the mixing efficiency index. In particular, we introduce a method to induce effective mixing in a microfluidic chamber by the actuation of the same beads to perform global swarming behavior, a collective motion of a large number of individual entities often seen in nature. The microparticle swarming induces high fluid velocities in initially stagnant fluids, and it can be externally controlled. The method is pilot-tested using a point-of-care test featuring a bioluminescent assay for the detection of antibodies. The mixing by the magnetic beads leads to increased assay kinetics, which indeed reduces the time to sensor readout substantially. Magnetic microparticle swarming is expected to be beneficial for a wide variety of point-of-care devices, where fast homogeneity of reagents does play a role.

Application of Microfluidics in Immunoassay: Recent Advancements

In recent years, point-of-care testing has played an important role in immunoassay, biochemical analysis, and molecular diagnosis, especially in low-resource settings. Among various point-of-care-testing platforms, microfluidic chips have many outstanding advantages. Microfluidic chip applies the technology of miniaturizing conventional laboratory which enables the whole biochemical process including reagent loading, reaction, separation, and detection on the microchip. As a result, microfluidic platform has become a hotspot of research in the fields of food safety, health care, and environmental monitoring in the past few decades. Here, the state-of-the-art application of microfluidics in immunoassay in the past decade will be reviewed. According to different driving forces of fluid, microfluidic platform is divided into two parts: passive manipulation and active manipulation. In passive manipulation, we focus on the capillary-driven microfluidics, while in active manipulation, we introduce pressure microfluidics, centrifugal microfluidics, electric microfluidics, optofluidics, magnetic microfluidics, and digital microfluidics. Additionally, within the introduction of each platform, innovation of the methods used and their corresponding performance improvement will be discussed. Ultimately, the shortcomings of different platforms and approaches for improvement will be proposed.

Mixing during Trapping Enabled a Continuous-Flow Microfluidic Smartphone Immunoassay Using Acoustic Streaming

Smartphone-enabled microfluidic chemiluminescence immunoassay is a promising portable system for point-of-care (POC) biosensing applications. However, due to the rather faint emitted light in such a limited sample volume, it is still difficult to reach the clinically accepted range when the smartphone serves as a standalone detector. Besides, the multiple separation and washing steps during sample preparation hinder the immunoassay's applications for POC usage. Herein, we proposed a novel acoustic streaming tweezers-enabled microfluidic immunoassay, where the probe particles' purification, reaction, and sensing were simply achieved on the same chip at continuous-flow conditions. The dedicatedly designed high-speed microscale vortexes not only enable dynamic trapping and washing of the probe particles on-demand but also enhance the capture efficiency of the heterogeneous particle-based immunoassay through active mixing during trapping. The enriched probe particles and enhanced biomarker capture capability increase the local chemiluminescent light intensity and enable direct capture of the immunobinding signal by a regular smartphone camera. The system was tested for prostate-specific antigen (PSA) sensing both in buffer and serum, where a limit of detection of 0.2 ng/mL and a large dynamic response range from 0.3 to 10 ng/mL using only 10 μL of sample were achieved in a total assay time of less than 15 min. With the advantages of on-chip integration of sample preparation and detection and high sensing performance, the developed POC platform could be applied for many on-site diagnosis applications.

Biosensors and Bioanalytical Devices based on Magnetic Particles: A Review

Magnetic particles play an important role in current technology, and this field of technology extends to a broader progression. The term magnetic particles typically cover the paramagnetic particles and super-paramagnetic particles. Various materials like iron oxide are common, but other materials are available as well; a survey of such materials has been included in this work. They can serve for technological purposes like separation and isolation of chemical products or toxic waste, their use in the diagnosis of pathologies, drug delivery and other similar applications. In this review, biosensors, bioanalytical devices and bioassays, have been discussed. Materials for magnetic particles preparation, methods of assay, biosensors and bioassays working in stationary as well as flow-through arrangements are described here. A survey of actual literature has been provided as well.

Nonspecific Binding-Fundamental Concepts and Consequences for Biosensing Applications

Nature achieves differentiation of specific and nonspecific binding in molecular interactions through precise control of biomolecules in space and time. Artificial systems such as biosensors that rely on distinguishing specific molecular binding events in a sea of nonspecific interactions have struggled to overcome this issue. Despite the numerous technological advancements in biosensor technologies, nonspecific binding has remained a critical bottleneck due to the lack of a fundamental understanding of the phenomenon. To date, the identity, cause, and influence of nonspecific binding remain topics of debate within the scientific community. In this review, we discuss the evolution of the concept of nonspecific binding over the past five decades based upon the thermodynamic, intermolecular, and structural perspectives to provide classification frameworks for biomolecular interactions. Further, we introduce various theoretical models that predict the expected behavior of biosensors in physiologically relevant environments to calculate the theoretical detection limit and to optimize sensor performance. We conclude by discussing existing practical approaches to tackle the nonspecific binding challenge in vitro for biosensing platforms and how we can both address and harness nonspecific interactions for in vivo systems.

Particle actuation by rotating magnetic fields in microchannels: a numerical study

Magnetic particles confined in microchannels can be actuated to perform translation motion using a rotating magnetic field, but their actuation in such a situation is not yet well understood. Here, the actuation of a ferromagnetic particle confined in square microchannels is studied using immersed-boundary lattice Boltzmann simulations. In wide channels, when a sphere is positioned close to a side wall but away from channel corners, it experiences a modest hydrodynamic actuation force parallel to the channel walls. This force decreases as the sphere is shifted toward the bottom wall but the opposite trend is found when the channel is narrow. When the sphere is positioned midway between the top and bottom channel walls, the actuation force decreases as the channel width decreases and can reverse its direction. These phenomena are elucidated by studying the flow and pressure fields in the channel-particle system and by analyzing the viscous and pressure components of the hydrodynamic force acting on different parts of the sphere.

Design of micromagnetic arrays for on-chip separation of superparamagnetic bead aggregates and detection of a model protein and double-stranded DNA analytes

Magnetically actuated lab-on-a-chip (LOC) technologies have enabled rapid, highly efficient separation of specific biomarkers and cells from complex biological samples. Nonlinear magnetophoresis (NLM) is a technique that uses a microfabricated magnet array (MMA) and a time varying external magnetic field to precisely control the transport of superparamagnetic (SPM) beads on the surface of a chip based on their size and magnetization. We analyze the transport and separation behavior of SPM monomers and dimers on four MMA geometries, i.e., circular, triangular, square and rectangular shaped micromagnets, across a range of external magnetic field rotation frequencies. The measured critical frequency of the SPM beads on an MMA, i.e., the velocity for which the hydrodynamic drag on a bead exceeds the magnetic force, is closely related to the local magnetic flux density landscape on a micromagnet in the presence of an external magnetic field. A set of design criteria has been established for the optimization of MMAs for NLM separation, with particular focus on the shape of the micromagnets forming the array. The square MMA was used to detect a model protein biomarker and gene fragment based on a magnetic bead assembly (MBA) assay. This assay uses ligand functionalized SPM beads to capture and directly detect an analyte through the formation of SPM bead aggregates. These beads aggregates were detected through NLM separation and microscopic analysis resulting in a highly sensitive assay that did not use carrier fluid.

An integrated actuating and sensing system for light-addressable potentiometric sensor (LAPS) and light-actuated AC electroosmosis (LACE) operation

To develop a lab on a chip (LOC) integrated with both sensor and actuator functions, a novel two-in-one system based on optical-driven manipulation and sensing in a microfluidics setup based on a hydrogenated amorphous silicon (a-Si:H) layer on an indium tin oxide/glass is first realized. A high-intensity discharge xenon lamp functioned as the light source, a chopper functioned as the modulated illumination for a certain frequency, and a self-designed optical path projected on the digital micromirror device controlled by the digital light processing module was established as the illumination input signal with the ability of dynamic movement of projected patterns. For light-addressable potentiometric sensor (LAPS) operation, alternating current (AC)-modulated illumination with a frequency of 800 Hz can be generated by the rotation speed of the chopper for photocurrent vs bias voltage characterization. The pH sensitivity, drift coefficient, and hysteresis width of the Si₃N₄ LAPS are 52.8 mV/pH, -3.2 mV/h, and 10.5 mV, respectively, which are comparable to the results from the conventional setup. With an identical two-in-one system, direct current illumination without chopper rotation and an AC bias voltage can be provided to an a-Si:H chip with a manipulation speed of 20 μm/s for magnetic beads with a diameter of 1 μm. The collection of magnetic beads by this light-actuated AC electroosmosis (LACE) operation at a frequency of 10 kHz can be easily realized. A fully customized design of an illumination path with less decay can be suggested to obtain a high efficiency of manipulation and a high signal-to-noise ratio of sensing. With this proposed setup, a potential LOC system based on LACE and LAPS is verified with the integration of a sensor and an actuator in a microfluidics setup for future point-of-care testing applications.

Detection of pathogenic bacteria by magneto-immunoassays: a review

Magnetic particle-based immunoassays are widely used in microbiology-related assays for both microbial capture, separation, analysis, and detection. Besides facilitating sample operation, the implementation of micro-to-nanometer scale magnetic beads as a solid support potentially shortens the incubation time (for magnetic immuno capture) from several hours to less than an hour. Analytical technologies based on magnetic beads offer a rapid, effective and inexpensive way to separate and concentrate the target analytes prior to detection. Magneto-immuno separation uses magnetic particles coated with specific antibodies to capture target microorganisms, bear the corresponding antigens, and subsequently separate them from the sample matrix in a magnetic field. The method has been proven effective in separating various types of pathogenic bacteria from environmental water samples and in eliminating background interferences. Magnetic particles are often used to capture target cells (pathogenic bacteria) from samples. In most commercially available assays, the actual identification and quantitation of the captured cells is then performed by classical microbiological assays. This review highlights the most sensitive analytic methods (i.e., long-range surface plasmon resonance and electrochemical impedance spectroscopy) to detect magnetically tagged bacteria in conjunction with magnetic actuation.

Baleen-Mimicking Virtual Filters for Rapid Detection of Pathogenic Bacteria in Water Using Magnetic Nanoparticle Chains and a Halbach Ring

We have developed a virtual filter that quickly and efficiently captures and detects pathogenic bacteria in large amounts of water. The virtual filter comprised magnetic nanoparticle chains (MNCs) obtained by cross-linking alginate-coated magnetic nanoparticles (MNPs). When the MNC solution in a disposable plastic tube was exposed to an external magnetic field, the MNCs were aligned along the magnetic field lines, forming a filter similar to a whale's baleen filtering system. A Halbach ring that increased the magnetic field inside the ring was used as the source of an external magnetic field. The Halbach ring produced a more uniform and denser alignment of MNCs than any other ring array. To demonstrate the performance of the virtual filter comprising MNCs, Escherichia coli (E. coli) O157-spiked water was injected into the virtual filter comprising polyethyleneimine-coated MNCs, and the concentration of E. coli O157 captured by electrostatic interaction was determined using qPCR analysis. The bacterial capture efficiency using MNCs was 90% at a flow rate of 5 mL/min, and the detection limit after 10 min of preconcentration of bacteria was 10 cfu/mL, which is 100 times lower than that obtained using qPCR alone.

Comparison of magnetic bead surface functionalities for the immunopurification of growth hormone-releasing hormones prior to liquid chromatography-high resolution mass spectrometry

Growth hormone-releasing hormone and its analogues sermorelin, tesamorelin and CJC-1295 are included in the prohibited list of the World Antidoping Agency. These target peptides are found at very low concentrations in urine (at the pg/mL level). For this reason, hyphenated enrichment and purification steps prior to mass spectrometric detection are required. Among different strategies, immunopurification based on magnetic beads is an excellent alternative, as it offers improved selectivity when the immunoreactivity and orientation of the antibody are optimum and non-specific adsorption is minimized. However, choosing the magnetic bead surface functionalities that provide the best recoveries is not so straightforward. In this work, we have evaluated the suitability of magnetic beads with different supports, binding capacities and affinity chemistries prior analysis of human urine samples by liquid chromatography coupled to high resolution mass spectrometry using a Quadrupole-Orbitrap instrument. After optimization of the immunopurification protocol with the magnetic beads that provided better recoveries, the method was fully validated and found to be adequate considering the parameters specificity, intra- and inter-day precision (lower than 15 and 25%, respectively), matrix effect, limit of detection (0.2 ng/mL) and limit of identification (0.5 ng/mL).

A Prominent Cell Manipulation Technique in BioMEMS: Dielectrophoresis

BioMEMS, the biological and biomedical applications of micro-electro-mechanical systems (MEMS), has attracted considerable attention in recent years and has found widespread applications in disease detection, advanced diagnosis, therapy, drug delivery, implantable devices, and tissue engineering. One of the most essential and leading goals of the BioMEMS and biosensor technologies is to develop point-of-care (POC) testing systems to perform rapid prognostic or diagnostic tests at a patient site with high accuracy. Manipulation of particles in the analyte of interest is a vital task for POC and biosensor platforms. Dielectrophoresis (DEP), the induced movement of particles in a non-uniform electrical field due to polarization effects, is an accurate, fast, low-cost, and marker-free manipulation technique. It has been indicated as a promising method to characterize, isolate, transport, and trap various particles. The aim of this review is to provide fundamental theory and principles of DEP technique, to explain its importance for the BioMEMS and biosensor fields with detailed references to readers, and to identify and exemplify the application areas in biosensors and POC devices. Finally, the challenges faced in DEP-based systems and the future prospects are discussed.

Combined Force-Torque Spectroscopy of Proteins by Means of Multiscale Molecular Simulation

Assessing the structural properties of large proteins is important to gain an understanding of their function in, e.g., biological systems or biomedical applications. We propose a method to examine the mechanical properties of proteins subject to applied forces by means of multiscale simulation. Both stretching and torsional forces are considered, and these may be applied independently of each other. As a proof of principle, we apply torsional forces to a coarse-grained continuum model of the antibody protein immunoglobulin G using fluctuating finite element analysis and use it to identify the area of strongest deformation. This region is essential to the torsional properties of the molecule as a whole because it represents the softest, most deformable domain. Zooming in, this part of the molecule is subjected to torques and stretching forces using molecular dynamics simulations on an atomistically resolved level to investigate its torsional properties. We calculate the torsional resistance as a function of the rotation of the domain while subjecting it to various stretching forces. From this, we assess how the measured twist-torque profiles develop with increasing stretching force and show that they exhibit torsion stiffening, in qualitative agreement with experimental findings. We argue that combining the twist-torque profiles for various stretching forces effectively results in a combined force-torque spectroscopy analysis, which may serve as a mechanical signature for a biological macromolecule.

Advances in Electrochemical Aptasensors Based on Carbon Nanomaterials

Carbon nanomaterials offer unique opportunities for the assembling of electrochemical aptasensors due to their high electroconductivity, redox activity, compatibility with biochemical receptors and broad possibilities of functionalization and combination with other auxiliary reagents. In this review, the progress in the development of electrochemical aptasensors based on carbon nanomaterials in 2016–2020 is considered with particular emphasis on the role of carbon materials in aptamer immobilization and signal generation. The synthesis and properties of carbon nanotubes, graphene materials, carbon nitride, carbon black particles and fullerene are described and their implementation in the electrochemical biosensors are summarized. Examples of electrochemical aptasensors are classified in accordance with the content of the surface layer and signal measurement mode. In conclusion, the drawbacks and future prospects of carbon nanomaterials’ application in electrochemical aptasensors are briefly discussed.

Static and dynamic behavior of magnetic particles at fluid interfaces

This perspective work reviews the current status of research on magnetic particles at fluid interfaces. The article gives both a unified overview of recent experimental advances and theoretical studies centered on very different phenomena that share a common characteristic: they involve adsorbed magnetic particles that range in size from a few nanometers to several millimeters. Because of their capability of being remotely piloted through controllable external fields, magnetic particles have proven essential as building blocks in the design of new techniques, smart materials and micromachines, with new tunable properties and prospective applications in engineering and biotechnology. Once adsorbed at a fluid-fluid interfase, in a process that can be facilitated via the application of magnetic field gradients, these particles often result sorely confined to two dimensions (2D). In this configuration, inter-particle forces directed along the perpendicular to the interface are typically very small compared to the surface forces. Hence, the confinement and symmetry breaking introduced by the presence of the surface play an important role on the response of the system to the application of an external field. In monolayers of particles where the magnetic is predominant interaction, the states reached are strongly determined by the mode and orientation of the applied field, which promote different patterns and processes. Furthermore, they can reproduce some of the dynamic assemblies displayed in bulk or form new ones, that take advantage of the interfacial phenomena or of the symmetry breaking introduce by the confining boundary. Magnetic colloids are also widely used for unraveling the guiding principles of 2D dynamic self-assembly, in designs devised for producing interface transport, as tiny probes for assessing interfacial rheological properties, neglecting the bulk and inertia contributions, as well as actuated stabilizing agents in foams and emulsions.

Convection-driven microfabricated hydrogels for rapid biosensing

A microscale biosensing platform using rehydration-mediated swelling of bio-functionalized hydrogel structures and rapid target analyte capture is described. Induced convective flow mitigates diffusion limited incubation times, enabling model assays to be completed in under three minutes. Assay design parameters have been evaluated, revealing fabrication criteria required to tune detection sensitivity.

Optical detection of the magnetophoretic transport of superparamagnetic beads on a micromagnetic array

Micromagnetic arrays (MMAs) have proven to be powerful tools for controlling the transport and separation of bioanalytes, i.e., they allow bioanalyte-superparamagnetic (SPM) bead complexes of specific size and magnetization to be moved in a synchronized manner that is precisely controlled with the orientation of an external magnetic field. This article presents a laser-photodetector system for the simple detection of individual SPM beads moving on a specific region of an MMA. This system detects the SPM beads through the change in intensity of reflective light as they move from the highly reflective micromagnetics to the supporting substrate. We demonstrate that this opti-MMA system allowed the size, number, and magnetic and optical properties of the SPM beads to be rapidly determined for regions > 49 µm² in size. The response of the opti-MMA system was characterized in several optical configurations to develop a theoretical description of its sensitivity and dynamic range. The speed, low-cost, and sensitivity of this system promises to allow MMAs to be readily applied in in vitro diagnostics and biosensing.

Magnetic particles for integrated nucleic acid purification, amplification and detection without pipetting

Nucleic acid amplification based detection plays an important role in food safety, environmental monitoring and clinical diagnosis. However, traditional nucleic acid detection process involves transferring liquid from one tube to another by pipetting. It requires trained persons, equipped labs and consumes lots of time. The ideal nucleic acid detection is integrated, closed, simplified and automated. Magnetic particles actuated by magnetic fields can efficiently adsorb nucleic acids and promote integrated nucleic acid assays without pipetting driven by pumps and centrifuges. We will comprehensively review magnetic particles assisted integrated system for nucleic acid detection and hope it can inspire further related study.

Passive micropumping in microfluidics for point-of-care testing

Suitable micropumping methods for flow control represent a major technical hurdle in the development of microfluidic systems for point-of-care testing (POCT). Passive micropumping for point-of-care microfluidic systems provides a promising solution to such challenges, in particular, passive micropumping based on capillary force and air transfer based on the air solubility and air permeability of specific materials. There have been numerous developments and applications of micropumping techniques that are relevant to the use in POCT. Compared with active pumping methods such as syringe pumps or pressure pumps, where the flow rate can be well-tuned independent of the design of the microfluidic devices or the property of the liquids, most passive micropumping methods still suffer flow-control problems. For example, the flow rate may be set once the device has been made, and the properties of liquids may affect the flow rate. However, the advantages of passive micropumping, which include simplicity, ease of use, and low cost, make it the best choice for POCT. Here, we present a systematic review of different types of passive micropumping that are suitable for POCT, alongside existing applications based on passive micropumping. Future trends in passive micropumping are also discussed.

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

The development of magnetic field sensors for biomedical applications primarily focuses on equivalent magnetic noise reduction or overall design improvement in order to make them smaller and cheaper while keeping the required values of a limit of detection. One of the cutting-edge topics today is the use of magnetic field sensors for applications such as magnetocardiography, magnetotomography, magnetomyography, magnetoneurography, or their application in point-of-care devices. This introductory review focuses on modern magnetic field sensors suitable for biomedicine applications from a physical point of view and provides an overview of recent studies in this field. Types of magnetic field sensors include direct current superconducting quantum interference devices, search coil, fluxgate, magnetoelectric, giant magneto-impedance, anisotropic/giant/tunneling magnetoresistance, optically pumped, cavity optomechanical, Hall effect, magnetoelastic, spin wave interferometry, and those based on the behavior of nitrogen-vacancy centers in the atomic lattice of diamond.

Direct identification of the herpes simplex virus UL27 gene through single particle manipulation and optical detection using a micromagnetic array

Magnetophoretic lab on a chip technologies are rapidly evolving into integrated systems for the identification of biomarkers and cells with ultra-high sensitivity. We demonstrate the highly efficient detection of the Human herpes simplex virus type 1 (HSV) UL27 gene through the programmed assembly of superparamagnetic (SPM) nanoparticles based on oligonucleotide hybridization. The state of assembly of the SPM nanoparticles was determined by optical signature of the synchronized motion on the beads on a micromagnetic array (MMA). This technique has been used to identify <200 copies of the HSV UL27 gene without amplification in less than 20 minutes. The MAA can also be used to separate gene-SPM bead aggregates from millions of unreacted SPM beads based on nonlinear magnetophoresis (NLM). The MMA-optical detection system promises to enable highly sensitive, nucleic acid analysis to be performed without amplification and with the consumption of minimal amounts of reagent.

Performance Validation of a Planar Hall Resistance Biosensor through Beta-Amyloid Biomarker

Magnetic sensors have great potential for biomedical applications, particularly, detection of magnetically-labeled biomolecules and cells. On the basis of the advantage of the planar Hall effect sensor, which consists of improved thermal stability as compared with other magnetic sensors, we have designed a portable biosensor platform that can detect magnetic labels without applying any external magnetic field. The trilayer sensor, with a composition of Ta (5 nm)/NiFe (10 nm)/Cu (x = 0 nm~1.2 nm)/IrMn (10 nm)/Ta (5 nm), was deposited on a silicon wafer using photolithography and a sputtering system, where the optimized sensor sensitivity was 6 μV/(Oe∙mA). The detection of the magnetic label was done by comparing the signals obtained in first harmonic AC mode (1f mode) using an external magnetic field and in the second harmonic AC mode (2f mode) with a self-field generated by current passing through the sensor. In addition, a technique for the β-amyloid biomarker-based antibody-antigen sandwich model was demonstrated for the detection of a series of concentrations of magnetic labels using the self-field mode method, where the signal-to-noise ratio (SNR) was high. The generated self-field was enough to detect an immobilized magnetic tag without an additional external magnetic field. Hence, it could be possible to reduce the device size to use the point-of-care testing using a portable circuit system.

Design and Fabrication of a PDMS-Based Manual Micro-Valve System for Microfluidic Applications

In this study, a manual micro-valve system (dimension: w × h: 1000 × 50 μm with 8-integrated channel valves was designed for controlling up to 8 different flows of agents (including magnetic nanoparticle flow) injected into the mixture zone of the microfluidics. The working parts of the micro-valve and microfluidic channel were fabricated from Poly(dimethyl siloxane) materials. The aperture of each channel valve was manually manipulated by a screw and a support kit (made of Plexiglas® materials). This valve system was connected to a microfluidic device with two important modules: a multi-liquid mixing component and a micro-reactor (~5 μL of volume). The study on controlling liquid flows proved that this valve system was effective for the experiments on the flow mixing and delivering the reactants into the micro-reaction chamber in order. The results are the first step for the fabrication of liquid flow controllers in integrated microfluidic systems towards biological analysis applications.

Lab-on-a-Chip Devices for Point-of-Care Medical Diagnostics

The recent coronavirus (COVID-19) pandemic has underscored the need to move from traditional lab-centralized diagnostics to point-of-care (PoC) settings. Lab-on-a-chip (LoC) platforms facilitate the translation to PoC settings via the miniaturization, portability, integration, and automation of multiple assay functions onto a single chip. For this purpose, paper-based assays and microfluidic platforms are currently being extensively studied, and much focus is being directed towards simplifying their design while simultaneously improving multiplexing and automation capabilities. Signal amplification strategies are being applied to improve the performance of assays with respect to both sensitivity and selectivity, while smartphones are being integrated to expand the analytical power of the technology and promote its accessibility. In this chapter, we review the main technologies in the field of LoC platforms for PoC medical diagnostics and survey recent approaches for improving these assays.