Active pneumatic control of centrifugal microfluidic flows for lab-on-a-chip applications

Microfluidic methods for the diagnosis of acute respiratory tract infections

Acute respiratory tract infections (ARTIs) are caused by sporadic or pandemic outbreaks of viral or bacterial pathogens, and continue to be a considerable socioeconomic burden for both developing and industrialized countries alike. Diagnostic methods and technologies serving as the cornerstone for disease management, epidemiological tracking, and public health interventions are evolving continuously to keep up with the demand for higher sensitivity, specificity and analytical throughput. Microfluidics is becoming a key technology in these developments as it allows for integrating, miniaturizing and automating bioanalytical assays at an unprecedented scale, reducing sample and reagent consumption and improving diagnostic performance in terms of sensitivity, throughput and response time. In this article, we describe relevant ARTIs-pneumonia, influenza, severe acute respiratory syndrome, and coronavirus disease 2019-along with their pathogenesis. We provide a summary of established methods for disease diagnosis, involving nucleic acid amplification techniques, antigen detection, serological testing as well as microbial culture. This is followed by a short introduction to microfluidics and how flow is governed at low volume and reduced scale using centrifugation, pneumatic pumping, electrowetting, capillary action, and propagation in porous media through wicking, for each of these principles impacts the design, functioning and performance of diagnostic tools in a particular way. We briefly cover commercial instruments that employ microfluidics for use in both laboratory and point-of-care settings. The main part of the article is dedicated to emerging methods deriving from the use of miniaturized, microfluidic systems for ARTI diagnosis. Finally, we share our thoughts on future perspectives and the challenges associated with validation, approval, and adaptation of microfluidic-based systems.

Sample-to-answer centrifugal microfluidic droplet PCR platform for quantitation of viral load

Droplet digital polymerase chain reaction (ddPCR) stands out as a highly sensitive diagnostic technique that is gaining traction in infectious disease diagnostics due to its ability to quantitate very low numbers of viral gene copies. By partitioning the sample into thousands of droplets, ddPCR enables precise and absolute quantification without relying on a standard curve. However, current ddPCR systems often exhibit relatively low levels of integration, and the analytical process remains dependent on elaborate workflows for up-front sample preparation. Here, we introduce a fully-integrated system seamlessly combining viral lysis, RNA extraction, emulsification, reverse transcription (RT) ddPCR, and fluorescence readout in a sample-to-answer format. The system comprises a disposable microfluidic cartridge housing buffers and reagents required for the assay, and a centrifugal platform that allows for pneumatic actuation of liquids during rotation, enabling automation of the workflow. Highly monodisperse droplets (∼50 μm in diameter) are produced using centrifugal step emulsification and automatically transferred to an integrated heating module for target amplification. The platform is equipped with a miniature fluorescence imaging system enabling on-chip read-out of droplets after RT-ddPCR. We demonstrate sample-to-answer detection of SARS-CoV-2 N and E genes, along with RNase P endogenous reference, using hydrolysis probes and multiplexed amplification within single droplets for concentrations as low as 0.1 copy per μL. We also tested 14 nasopharyngeal swab specimens from patients and were able to distinguish positive and negative SARS-CoV-2 samples with 100% accuracy, surpassing results obtained by conventional real-time amplification.

Reagent storage and delivery on integrated microfluidic chips for point-of-care diagnostics

Microfluidic-based point-of-care diagnostics offer several unique advantages over existing bioanalytical solutions, such as automation, miniaturisation, and integration of sensors to rapidly detect on-site specific biomarkers. It is important to highlight that a microfluidic POC system needs to perform a number of steps, including sample preparation, nucleic acid extraction, amplification, and detection. Each of these stages involves mixing and elution to go from sample to result. To address these complex sample preparation procedures, a vast number of different approaches have been developed to solve the problem of reagent storage and delivery. However, to date, no universal method has been proposed that can be applied as a working solution for all cases. Herein, both current self-contained (stored within the chip) and off-chip (stored in a separate device and brought together at the point of use) are reviewed, and their merits and limitations are discussed. This review focuses on reagent storage devices that could be integrated with microfluidic devices, discussing further issues or merits of these storage solutions in two different sections: direct on-chip storage and external storage with their application devices. Furthermore, the different microvalves and micropumps are considered to provide guidelines for designing appropriate integrated microfluidic point-of-care devices.

Automated sample preparation for electrospray ionization mass spectrometry based on CLOCK-controlled autonomous centrifugal microfluidics

We report a centrifugal microfluidic device that automatically performs sample preparation under steady-state rotation for clinical applications using mass spectrometry. The autonomous microfluidic device was designed for the control of liquid operation on centrifugal hydrokinetics (CLOCK) paradigm. The reported device was highly stable, with less than 7% variation with respect to the time of each unit operation (sample extraction, mixing, and supernatant extraction) in the preparation process. An agitation mechanism with bubbling was used to mix the sample and organic solvent in this device. We confirmed that the device effectively removed the protein aggregates from the sample, and the performance was comparable to those of conventional manual sample preparation procedures that use high-speed centrifugation. In addition, probe electrospray ionization mass spectrometry (PESI-MS) was performed to compare the device-treated and manually treated samples. The obtained PESI-MS spectra were analyzed by partial least squares discriminant analysis, and the preparation capability of the device was found to be equivalent to that of the conventional method.

Fast and on-site animal species identification in processed meat via centrifugal microfluidics and isothermal amplification

We present a novel centrifugal microfluidic approach to rapidly identify animal species in meat products. The workflow requires a centrifugal cartridge for DNA extraction and for preparation of a recombinant polymerase amplification (RPA) reaction, a programmable centrifuge for processing the cartridge and an isothermal reader to perform the RPA. Liquid reagents are pre-stored on the cartridge and the meat sample can be added directly without any pre-treatment. With this system, we are able to identify six different animal species in a single run within one hour. In pork salami containing horse, turkey, sheep, chicken and beef meat, it was possible to identify species levels as low as 0.01%. In beef salami and cooked pork sausages 0.1% of foreign meat could be detected. This novel workflow enables rapid and sensitive species identification in processed meat at the point of need.

Centrifugal microfluidic system for colorimetric sample-to-answer detection of viral pathogens

We describe a microfluidic system for conducting thermal lysis, polymerase chain reaction (PCR) amplification, hybridization, and colorimetric detection of foodborne viral organisms in a sample-to-answer format. The on-chip protocol entails 24 steps which are conducted by a centrifugal platform that allows for actuating liquids pneumatically during rotation and so facilitates automation of the workflow. The microfluidic cartridge is fabricated from transparent thermoplastic polymers and accommodates assay components along with an embedded micropillar array for detection and read-out. A panel of oligonucleotide primers and probes has been developed to perform PCR and hybridization assays that allows for identification of five different viruses, including pathogens such as norovirus and hepatitis A virus (HAV) in a multiplexed format using digoxigenin-labelled amplicons and immunoenzymatic conversion of a chromogenic substrate. Using endpoint detection, we demonstrate that the system can accurately and repetitively (n = 3) discriminate positive and negative signals for HAV at 350 genome copies per μL. As part of the characterization and optimization process, we show that the implementation of multiple (e.g., seven) micropillar arrays in a narrow fluidic pathway can lead to variation (up to 50% or more) in the distribution of colorimetric signal deriving from the assay. Numerical modeling of flow behaviour was used to substantiate these findings. The technology-by virtue of automation-can provide a pathway toward rapid detection of viral pathogens, shortening response time in food safety surveillance, compliance, and enforcement as well as outbreak investigations.

Low-High-Low Rotationally Pulse-Actuated Serial Dissolvable Film Valves Applied to Solid Phase Extraction and LAMP Isothermal Amplification for Plant Pathogen Detection on a Lab-on-a-Disc

The ability of the centrifugal Lab-on-a-Disc (LoaD) platform to closely mimic the "on bench" liquid handling steps (laboratory unit operations (LUOs)) such as metering, mixing, and aliquoting supports on-disc automation of bioassay without the need for extensive biological optimization. Thus, well-established bioassays, normally conducted manually using pipettes or using liquid handling robots, can be relatively easily automated in self-contained microfluidic chips suitable for use in point-of-care or point-of-use settings. The LoaD's ease of automation is largely dependent on valves that can control liquid movement on the rotating disc. The optimum valving strategy for a true low-cost and portable device is rotationally actuated valves, which are actuated by changes in the disc spin-speed. However, due to tolerances in disc manufacturing and variations in reagent properties, most of these valving technologies have inherent variation in their actuation spin-speed. Most valves are actuated through stepped increases in disc spin-speed until the motor reaches its maximum speed (rarely more than 6000 rpm). These manufacturing tolerances combined with this "analogue" mechanism of valve actuation limits the number of LUOs that can be placed on-disc. In this work, we present a novel valving mechanism called low-high-low serial dissolvable film (DF) valves. In these valves, a DF membrane is placed in a dead-end pneumatic chamber. Below an actuation spin-speed, the trapped air prevents liquid wetting and dissolving the membrane. Above this spin-speed, the liquid will enter and wet the DF and open the valve. However, as DFs take ∼40 s to dissolve, the membrane can be wetted, and the disc spin-speed reduced before the film opens. Thus, by placing valves in a series, we can govern on which "digital pulse" in spin-speeding a reagent is released; a reservoir with one serial valve will open on the first pulse, a reservoir with two serial valves on the second, and so on. This "digital" flow control mechanism allows the automation of complex assays with high reliability. In this work, we first describe the operation of the valves, outline the theoretical basis for their operation, and support this analysis with an experiment. Next, we demonstrate how these valves can be used to automate the solid-phase extraction of DNA on on-disc LAMP amplification for applications in plant pathogen detection. The disc was successfully used to extract and detect, from a sample lysed off-disc, DNA indicating the presence of thermally inactivated Clavibacter michiganensis ssp. michiganensis (Cmm), a bacterial pathogen on tomato leaf samples.

Automated centrifugal microfluidic system for the preparation of adaptor-ligated sequencing libraries

The intensive workload associated with the preparation of high-quality DNA libraries remains a key obstacle toward widespread deployment of sequencing technologies in remote and resource-limited areas. We describe the development of single-use microfluidic devices driven by an advanced pneumatic centrifugal microfluidic platform, the PowerBlade, to automate the preparation of Illumina-compatible libraries based on adaptor ligation methodology. The developed on-chip workflow includes enzymatic DNA fragmentation coupled to end-repair, adaptor ligation, first DNA cleanup, PCR amplification, and second DNA cleanup. This complex workflow was successfully integrated into simple thermoplastic microfluidic devices that are amenable to mass production with injection molding. The system was validated by preparing, on chip, libraries from a mixture of genomic DNA extracted from three common foodborne pathogens (Listeria monocytogenes, Escherichia coli and Salmonella enterica serovar Typhimurium) and comparing them with libraries made via a manual procedure. The two types of libraries were found to exhibit similar quality control metrics (including genome coverage, assembly, and relative abundances) and led to nearly uniform coverage independent of GC content. This microfluidic technology offers a time-saving and cost-effective alternative to manual procedures and robotic-based automation, making it suitable for deployment in remote environments where technical expertise and resources might be scarce. Specifically, it facilitates field practices that involve mid- to low-throughput sequencing, such as tasks related to foodborne pathogen detection, characterization, and microbial profiling.

Method to fabricate round cross-sectional channel using thermal expansion of air for passive flow regulators

We present a novel method for fabricating round cross-sectional channels for autoregulatory pressure regulators. The application of previously reported methods in multilayered soft lithography using three-dimensional printed molds is challenging. Herein, we used a thermal expansion technique to create round cross-sectional channels in replica layers using air in the cavity space of a master mold. The width and height of the round channel in the replica could be adjusted in the range of 80-300 and 3-57 µm, respectively, by varying the precuring time of the replica in the gel state and adjusting the cavity size of the master mold. We successfully fabricated a pressure regulator with a round cross-sectional channel, achieving a constant output pressure at a low threshold input pressure. Our device exhibited superior performance, with a constant output pressure at a threshold input pressure of less than 77%, compared to a device with a rectangular cross-sectional channel. Our method has significant potential for application in the fabrication of integrated microfluidic systems with round cross-sectional channels.

Digital process control of multi-step assays on centrifugal platforms using high-low-high rotational-pulse triggered valving

Due to their capability for comprehensive sample-to-answer automation, the interest in centrifugal microfluidic systems has greatly increased in industry and academia over the last quarter century. The main applications of these "Lab-on-a-Disc" (LoaD) platforms are in decentralised bioanalytical point-of-use / point-of-care testing. Due to the unidirectional and omnipresent nature of the centrifugal force, advanced flow control is key to coordinate multi-step / multi-reagent assay formats on the LoaD. Formerly, flow control was often achieved by capillary burst valves which require gradual increments of the spin speed of the system-innate spindle motor. Recent advanced introduced a flow control scheme called 'rotational pulse actuated valves'. In these valves the sequence of valve actuation is determined by the architecture of the disc while actuation is triggered by freely programmable upward spike (i.e. Low-High-Low (LHL)) in the rotational frequency. This paradigm shift from conventional 'analogue' burst valves to 'digital' pulsing significantly increases the number of sequential while also improving the overall robustness of flow control. In this work, we expand on these LHL valves by introducing High-Low-High (HLH) pulse-actuated (PA) valving which are actuated by 'downward' spike in the disc spin-rate. These HLH valves are particularly useful for high spin-rate operations such as centrifugation of blood. We introduce two different HLH architectures and then combine the most promising with LHL valves to implement the time-dependent liquid handling protocol underlying a common liver function test panel.

Acoustic Atomization-Induced Pumping Based on a Vibrating Sharp-Tip Capillary

Pumping is an essential component in many microfluidic applications. Developing simple, small-footprint, and flexible pumping methods is of great importance to achieve truly lab-on-a-chip systems. Here, we report a novel acoustic pump based on the atomization effect induced by a vibrating sharp-tip capillary. As the liquid is atomized by the vibrating capillary, negative pressure is generated to drive the movement of fluid without the need to fabricate special microstructures or use special channel materials. We studied the influence of the frequency, input power, internal diameter (ID) of the capillary tip, and liquid viscosity on the pumping flow rate. By adjusting the ID of the capillary from 30 µm to 80 µm and the power input from 1 V_pp to 5 V_pp, a flow rate range of 3 to 520 µL/min can be achieved. We also demonstrated the simultaneous operation of two pumps to generate parallel flow with a tunable flow rate ratio. Finally, the capability of performing complex pumping sequences was demonstrated by performing a bead-based ELISA in a 3D-printed microdevice.

Effect of air bubbling on electroless Pd plating for the practical application of hydrogen selective membranes

In this study, an air bubbling electroless plating (ELP) method was newly developed for the production of Pd composite membranes. The air bubble ELP alleviated the concentration polarization of Pd ions, making it possible to achieve a plating yield of 99.9% in 1 h and form very fine Pd grains with a uniform layer of ∼4.7 μm. A membrane with a diameter of 25.4 mm and a length of 450 mm was produced by the air bubbling ELP, achieving a hydrogen permeation flux of 4.0 × 10-1 mol m-2 s-1 and selectivity of ∼10 000 at 723 K with a pressure difference of 100 kPa. To confirm the reproducibility, six membranes were produced by the same method and assembled in a membrane reactor module to produce high-purity hydrogen by ammonia decomposition. Hydrogen permeation flux and selectivity of the six membranes at 723 K with a pressure difference of 100 kPa were 3.6 × 10-1 mol m-2 s-1 and ∼8900, respectively. An ammonia decomposition test with an ammonia feed rate of 12 000 mL min-1 showed that the membrane reactor produced hydrogen with >99.999% purity and a production rate of 1.01 Nm3 h-1 at 748 K with a retentate stream gauge pressure of 150 kPa and a permeation stream vacuum of -10 kPa. The ammonia decomposition tests confirmed that the newly developed air bubbling ELP method affords several advantages, such as rapid production, high ELP efficiency, reproducibility, and practical applicability.

Modular design of centrifugal microfluidic system and its application in nucleic acid screening

Modular integration of functional components on the chip and increasement in control accuracy through real-time alteration in the force direction of droplets is an effective way to optimize centrifugal microfluidic systems and realize passive components, compact modules, and high-throughput control. Conventional centrifugal microfluidic chips are mainly driven and controlled by centrifugal force and Euler force. The control valves are easily affected by machining precision, making the control unstable. In this study, a novel centrifugal microfluidic system is introduced to improve the freedom and accuracy of chip control while facilitating the design and addition of passive functional components. Furthermore, we modularize the centrifugal microfluidic chip to greatly shorten the period of design and optimization cycle and achieve chip reusability and multi-threaded control. Finally, to verify the feasibility of the modular centrifugal microfluidic chip applied to high-throughput nucleic acid screening, we test the nucleic acid purification and detection colorimetric reactions based on the modular centrifugal microfluidic chip. Among them, Chelex-100 is used to realize the purification of nucleic acid in cell lysate, and the purified solution can realize amplification in the PCR instrument, and the nucleic acid detection results are consistent with the off-chip kit by experimental testing. The system has great flexibility and stability under the acceptable purity of nucleic acid, which indicates that the platform has great potential for large-scale rapid screening applications.

Plant pathogen detection on a lab-on-a-disc using solid-phase extraction and isothermal nucleic acid amplification enabled by digital pulse-actuated dissolvable film valves

By virtue of its ruggedness, portability, rapid processing times, and ease-of-use, academic and commercial interest in centrifugal microfluidic systems has soared over the last decade. A key advantage of the LoaD platform is the ability to automate laboratory unit operations (LUOs) (mixing, metering, washing etc.) to support direct translation of 'on-bench' assays to 'on-chip'. Additionally, the LoaD requires just a low-cost spindle motor rather than specialized and expensive microfluidic pumps. Furthermore, when flow control (valves) is implemented through purely rotational changes in this same spindle motor (rather than using additional support instrumentation), the LoaD offers the potential to be a truly portable, low-cost and accessible platform. Current rotationally controlled valves are typically opened by sequentially increasing the disc spin-rate to a specific opening frequency. However, due lack of manufacturing fidelity these specific opening frequencies are better described as spin frequency 'bands'. With low-cost motors typically having a maximum spin-rate of 6000 rpm (100 Hz), using this 'analogue' approach places a limitation on the number of valves, which can be serially actuated thus limiting the number of LUOs that can be automated. In this work, a novel flow control scheme is presented where the sequence of valve actuation is determined by architecture of the disc while its timing is governed by freely programmable 'digital' pulses in its spin profile. This paradigm shift to 'digital' flow control enables automation of multi-step assays with high reliability, with full temporal control, and with the number of LUOs theoretically only limited by available space on the disc. We first describe the operational principle of these valves followed by a demonstration of the capability of these valves to automate complex assays by screening tomato leaf samples against plant pathogens. Reagents and lysed sample are loaded on-disc and then, in a fully autonomous fashion using only spindle-motor control, the complete assay is automated. Amplification and fluorescent acquisition take place on a custom spin-stand enabling the generation of real-time LAMP amplification curves using custom software. To prevent environmental contamination, the entire discs are sealed from atmosphere following loading with internal venting channels permitting easy movement of liquids about the disc. The disc was successfully used to detect the presence of thermally inactivated Clavibacter michiganensis. Michiganensis (CMM) bacterial pathogen on tomato leaf samples.

Technical and engineering considerations for designing therapeutics and delivery systems

The newly-emerged pathological conditions and increased rates of drug resistance necessitate application of the state-of-the-art technologies for accelerated discovery of the therapeutic candidates and obtaining comprehensive knowledge about their targets, action mechanisms, and interactions within the body including those between the receptors and drugs. Using the physics- and chemistry-based modern techniques for theranostic purposes, preparing smart carriers, local delivery of genes or drugs, and enhancing pharmaceutical bioavailability could be of great value against the hard-to-treat diseases and growing drug resistance. Besides the artificial intelligence- and quantum-based techniques, crystal engineering capable of designing new molecules with appropriate characteristics, improving the stability and bioavailability of poorly soluble drugs, and efficient carrier development could play a crucial role in manufacturing efficient pharmaceuticals and reducing the adverse events. In this context, identifying the structures and behaviors of crystals and predicting their characteristics are of great value. Electron diffraction by accelerated analysis of the chemicals and sensitivity to charge alterations, electromechanical tools for controlled delivery of therapeutics, mechatronics via fabrication of multi-functional smart products including the organ-on-chip devices for healthcare applications, and optomechatronics by overcoming the limitations of conventional biomedical techniques could address the unmet biomedical requirements and facilitate development of more effective theranostics with improved outcomes.

Automated sample-to-answer centrifugal microfluidic system for rapid molecular diagnostics of SARS-CoV-2

Testing for SARS-CoV-2 is one of the most important assets in COVID-19 management and mitigation. At the onset of the pandemic, SARS-CoV-2 testing was uniquely performed in central laboratories using RT-qPCR. RT-qPCR relies on trained personnel operating complex instrumentation, while time-to-result can be lengthy (e.g., 24 to 72 h). Now, two years into the pandemic, with the surge in cases driven by the highly transmissible Omicron variant, COVID-19 testing capabilities have been stretched to their limit worldwide. Rapid antigen tests are playing an increasingly important role in quelling outbreaks by expanding testing capacity outside the realm of clinical laboratories. These tests can be deployed in settings where repeat and rapid testing is essential, but they often come at the expense of limited accuracy and sensitivity. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) provides a number of advantages to SARS-CoV-2 testing in standard laboratories and at the point-of-need. In contrast to RT-qPCR, RT-LAMP is performed at a constant temperature, which circumvents the need for thermal cycling and translates into a shorter analysis time (e.g., <1 h). In addition, RT-LAMP is compatible with colorimetric detection, facilitating visualization and read-out. However, even with these benefits, RT-LAMP is not yet clinically deployed at its full capacity. Lack of automation and integration of sample preparation, such as RNA extraction, limits the sensitivity and specificity of the method. Furthermore, the need for cold storage of reagents complicates its use at the point of need. The developments presented in this work address these limitations: We describe a fully automated SARS-CoV-2 detection method using RT-LAMP, which also includes up-front lysis and extraction of viral RNA, performed on a centrifugal platform with active pneumatic pumping, a disposable, all-polymer-based microfluidic cartridge and lyophilized reagents. We demonstrate that the limit of detection of the RT-LAMP assay itself is 0.2 copies per μL using N and E genes as target sequences. When combined with integrated RNA extraction, the assay sensitivity is 0.5 copies per μL, which is highly competitive to RT-qPCR. We tested the automated assay using 12 clinical swab specimens from patients and were able to distinguish positive and negative samples for SARS-CoV-2 within 60 min, thereby obtaining 100% agreement with RT-qPCR results.

A film-lever actuated switch technology for multifunctional, on-demand, and robust manipulation of liquids

A lab-on-a-chip system with Point-of-Care testing capability offers rapid and accurate diagnostic potential and is useful in resource-limited settings where biomedical equipment and skilled professionals are not readily available. However, a Point-of-Care testing system that simultaneously possesses all required features of multifunctional dispensing, on-demand release, robust operations, and capability for long-term reagent storage is still a major challenge. Here, we describe a film-lever actuated switch technology that can manipulate liquids in any direction, provide accurate and proportional release response to the applied pneumatic pressure, as well as sustain robustness during abrupt movements and vibrations. Based on the technology, we also describe development of a polymerase chain reaction system that integrates reagent introduction, mixing and reaction functions all in one process, which accomplishes “sample-in-answer-out” performance for all clinical nasal samples from 18 patients with Influenza and 18 individual controls, in good concordance of fluorescence intensity with standard polymerase chain reaction (Pearson coefficients > 0.9). The proposed platform promises robust automation of biomedical analysis, and thus can accelerate the commercialization of a range of Point-of-Care testing devices.

Point-of-care testing offers rapid and accurate diagnostic potential being quite useful in resource-limited settings. Here, authors demonstrate a film-lever actuated switch technology for microfluidic manipulation enabling multifunctional dispensing, on-demand release, robust operation, and long-term storage.

Elastic membrane enabled inward pumping for liquid manipulation on a centrifugal microfluidic platform

Nowadays, centrifugal microfluidic platforms are finding wider acceptance for implementing point-of-care assays due to the simplicity of the controls, the versatility of the fluidic operations, and the ability to create a self-enclosed system, thus minimizing the risk of contamination for either the sample or surroundings. Despite these advantages, one of the inherent weaknesses of CD microfluidics is that all the sequential fluidic chambers and channels must be positioned radially since the centrifugal force acts from the center of the disk outward. Implementation of schemes where the liquid can be rerouted from the disk periphery to the disk center would significantly increase the utility of CD platforms and increase the rational utilization of the real estate on the disk. The present study outlines a novel utilization of elastic membranes covering fluidic chambers to implement inward pumping whereby the fluid is returned from the disk periphery to the center of the disk. When the disk revolves at an angular velocity of 3600 rpm, liquid enters the chamber covered by the elastic membrane. This membrane is deflected upward by liquid, storing energy like a compressed spring. When the angular velocity of the disk is reduced to 180 rpm and thus the centrifugal force is diminished, the elastic membrane pushes the liquid from the chamber inward, closer to the center of the disk. There are two channels leading from the elastic membrane-covered reservoir-one channel has a higher fluidic resistance and the other (wider) has a lower fluidic resistance. The geometry of these two channels determines the fluidic path inward (toward the center of the disk). Most of the liquid travels through the recirculating channel with lower resistance. We demonstrated an inward pumping efficiency in the range of 78%-89%. Elastic membrane-driven inward pumping was demonstrated for the application of enhanced fluid mixing. Additionally, to demonstrate the utility of the proposed pumping mechanism for multi-step assays on the disk, we implemented and tested a disk design that combines plasma separation and inward pumping.

On-the-Fly Phase Transition and Density Changes of Aqueous Two-Phase Systems on a Centrifugal Microfluidic Platform

This paper describes on-the-fly physical property changes of aqueous two-phase systems (ATPS) in microfluidic devices. The properties and phases of the ATPS are modulated on-demand by using a centrifugal microfluidic device filled with poly(ethylene glycol) (PEG) and dextran (DEX) solutions. By use of the centrifugal force and active pneumatic controls provided by a centrifugal microfluidic platform (CMP), PEG-DEX mixtures are manipulated and processed inside simple thermoplastic microfluidic devices. First, we experimentally demonstrate an on-chip ATPS transition from two phases to a single phase and vice versa by dynamically changing the concentration of the solution to bring ATPS across the binodal curve. We also demonstrate a density modulation scheme by introducing an ATPS solution mixed with sodium diatrizoate hydrate, which allows to increase the liquid density. By adding precisely metered volumes of water, we spontaneously change the density of the solution on the CMP and show that density marker microbeads fall into the solution according to their corresponding densities. The measured densities of ATPS show a good agreement with densities of microbeads and analytical plots. The results presented in this paper highlight the tremendous potential of CMPs for performing complex on-chip processing of ATPS. We anticipate that this method will be useful in applications such as microparticle-based plasma protein analysis and blood cell fractionation.

Systematic review of centrifugal valving based on digital twin modeling towards highly integrated lab-on-a-disc systems

Current, application-driven trends towards larger-scale integration (LSI) of microfluidic systems for comprehensive assay automation and multiplexing pose significant technological and economical challenges to developers. By virtue of their intrinsic capability for powerful sample preparation, centrifugal systems have attracted significant interest in academia and business since the early 1990s. This review models common, rotationally controlled valving schemes at the heart of such "Lab-on-a-Disc" (LoaD) platforms to predict critical spin rates and reliability of flow control which mainly depend on geometries, location and liquid volumes to be processed, and their experimental tolerances. In absence of larger-scale manufacturing facilities during product development, the method presented here facilitates efficient simulation tools for virtual prototyping and characterization and algorithmic design optimization according to key performance metrics. This virtual in silico approach thus significantly accelerates, de-risks and lowers costs along the critical advancement from idea, layout, fluidic testing, bioanalytical validation, and scale-up to commercial mass manufacture.

An automated centrifugal microfluidic assay for whole blood fractionation and isolation of multiple cell populations using an aqueous two-phase system

Fractionating whole blood and separating its constituent components one from another is an essential step in many clinical applications. Currently blood sample handling and fractionation processes remain a predominantly manual task that require well-trained operators to produce reliable and reproducible results. Herein, we demonstrate an advanced on-chip whole human blood fractionation and cell isolation process combining (i) an aqueous two-phase system (ATPS) to create complex separation layers with (ii) a centrifugal microfluidic platform (PowerBlade) with active pneumatic pumping to control and automate the assay. We use a polyethylene glycol (PEG) and dextran (DEX) mixture as the two-phase density gradient media and our automated centrifugal microfluidic platform to fractionate blood samples. Different densities of precisely tuned PEG-DEX solutions were tested to match each of the cell types typically targeted during blood fractionation applications. By employing specially designed microfluidic devices, we demonstrate the automation of the following steps: loading of a whole blood sample on-chip, layering of the blood on the ATPS solution, blood fractionation, precise radial repositioning of the fractionated layers, and finally extraction of multiple, selected fractionated components. Fractionation of up to six distinct layers is shown: platelet-rich plasma, buffy coat, PEG, DEX with neutrophils, red blood cells (RBCs) and high density gradient media (HDGM). Furthermore, through controlled dispensing of HDGM to the fractionation chamber, we show that each of the fractionated layers can be repositioned radially, on-the-fly, without disturbing the interfaces, allowing precise transfer of target fractions and cell types into external vials via a chip-to-world interface. Cell counting analysis and cell viability studies showed equivalence to traditional, manual methods. An overall cell viability greater than 90% of extracted cells demonstrates that the proposed approach is suitable for cell isolation applications. This proof-of-principle demonstration highlights the utility of the proposed system for automated whole blood fractionation and isolation for blood cell applications. We anticipate that the proposed approach will be a useful tool for many clinical applications such as standard cell isolation procedures and other bioanalytical assays (e.g., circulating tumor cells, and cell and gene therapy).

Secure Air Traffic Control at the Hub of Multiplexing on the Centrifugo-Pneumatic Lab-on-a-Disc Platform

Fluidic larger-scale integration (LSI) resides at the heart of comprehensive sample-to-answer automation and parallelization of assay panels for frequent and ubiquitous bioanalytical testing in decentralized point-of-use/point-of-care settings. This paper develops a novel "digital twin" strategy with an emphasis on rotational, centrifugo-pneumatic flow control. The underlying model systematically connects retention rates of rotationally actuated valves as a key element of LSI to experimental input parameters; for the first time, the concept of band widths in frequency space as the decisive quantity characterizing operational robustness is introduced, a set of quantitative performance metrics guiding algorithmic optimization of disc layouts is defined, and the engineering principles of advanced, logical flow control and timing are elucidated. Overall, the digital twin enables efficient design for automating multiplexed bioassay protocols on such "Lab-on-a-Disc" (LoaD) systems featuring high packing density, reliability, configurability, modularity, and manufacturability to eventually minimize cost, time, and risk of development and production.

Mixing characteristics of a bubble mixing microfluidic chip for genomic DNA extraction based on magnetophoresis: CFD simulation and experiment

Mixing a small amount of magnetic beads and regents with large volume samples evenly in microcavities of a microfluidic chip is always the key step for the application of microfluidic technology in the field of magnetophoresis analysis. This article proposes a microfluidic chip for DNA extraction by magnetophoresis, which relies on bubble rising to generate turbulence and microvortices of various sizes to mix magnetic beads with samples uniformly. The construction and working principle of the microfluidic chip are introduced. CFD simulations are conducted when magnetic beads and samples are irritated by the generation of gas bubbles with the variation of supply pressures. The whole mixing process in the microfluidic chip is observed through a high-speed camera and a microfluidic system when the gas bubbles are generated continuously. The influence of supply pressure on the mixing characteristics of the microfluidic chip is investigated and discussed with both simulation and experiments. Compared with magnetic mixing, bubble mixing can avoid the magnetic beads gather phenomenon caused by magnetic forces and provide a rapid and high efficient solution to realize mixing small amount of regents in large volume samples in a certain order without complex moving structures and operations in a chip. Two applications of mixing with the proposed microfluidic chip are also carried out and discussed.

An Overview on Microfluidic Systems for Nucleic Acids Extraction from Human Raw Samples

Nucleic acid (NA) extraction is a basic step for genetic analysis, from scientific research to diagnostic and forensic applications. It aims at preparing samples for its application with biomolecular technologies such as isothermal and non-isothermal amplification, hybridization, electrophoresis, Sanger sequencing and next-generation sequencing. Multiple steps are involved in NA collection from raw samples, including cell separation from the rest of the specimen, cell lysis, NA isolation and release. Typically, this process needs molecular biology facilities, specialized instrumentation and labor-intensive operations. Microfluidic devices have been developed to analyze NA samples with high efficacy and sensitivity. In this context, the integration within the chip of the sample preparation phase is crucial to leverage the promise of portable, fast, user-friendly and economic point-of-care solutions. This review presents an overview of existing lab-on-a-chip (LOC) solutions designed to provide automated NA extraction from human raw biological fluids, such as whole blood, excreta (urine and feces), saliva. It mainly focuses on LOC implementation aspects, aiming to describe a detailed panorama of strategies implemented for different human raw sample preparations.

An Integrated Centrifugal Degassed PDMS-Based Microfluidic Device for Serial Dilution

We propose an integrated serial dilution generator utilizing centrifugal force with a degassed polydimethylsiloxane (PDMS) microfluidic device. Using gas-soluble PDMS as a centrifugal microfluidic device material, the sample can be dragged in any arbitrary direction using vacuum-driven force, as opposed to in a single direction, without adding further actuation components. The vacuum-driven force allows the device to avoid the formation of air bubbles and exhibit high tolerance in the surface condition. The device was then used for sample metering and sample transferring. In addition, centrifugal force was used for sample loading and sample mixing. In this study, a series of ten-fold serial dilutions ranging from 100 to 10-4 with about 8 μL in each chamber was achieved, while the serial dilution ratio and chamber volume could easily be altered by changing the geometrical designs of the device. As a proof of concept of our hybrid approach with the centrifugal and vacuum-driven forces, ten-fold serial dilutions of a cDNA (complementary DNA) sample were prepared using the device. Then, the diluted samples were collected by fine needles and subject to a quantitative polymerase chain reaction (qPCR), and the results were found to be in good agreement with those for samples prepared by manual pipetting.

A microfluidic circuit consisting of individualized components with a 3D slope valve for automation of sequential liquid control

A microfluidic circuit on a disk platform, also known as lab-on-a-disk, is an integrated system for automated high-throughput screening for biochemical analysis. The microfluidic circuit on a disk performs biochemical analysis through sequential processes such as filtration, separation, detection, and synthesis of reagents. Sequential processes in microfluidic circuits operate through the systematically linked components, which include channels, valves, and chambers. The microchannels should have micrometer-scale for precise micro-volume liquid control in the microfluidic circuit on a disk. However, it is difficult to also consider productivity in the traditional technology. In addition, as the channel length increases, much effort is required to construct the components of the microfluidic circuit in the limited space of the disk. 3D printing is drawing attention as a microfluidic channel fabrication technique in order to overcome the physical limitations of the traditional methods. A new concept of a 3D slope valve has been developed, which performs precise and sequential micro-volume liquid control through centrifugal and gravitational forces. Micro-volumes of liquids in a slope valve-equipped circuit are controlled over a wide range of angular velocities through the control of the valve geometry, types of liquid and volume. For sequential micro-volume of liquid control, three lines of assembled modules are connected to a microfluidic circuit. In the microfluidic circuit with slope valves, the detection of fluorescent dye tagged-VEGF is possible through sequential mixing and reaction processes. As a result, micro-volume liquid is successfully controlled with high accuracy using the 3D microfluidic circuit with a slope valve.

Biosensing on the Centrifugal Microfluidic Lab-on-a-Disc Platform

Lab-on-a-Disc (LoaD) biosensors are increasingly a promising solution for many biosensing applications. In the search for a perfect match between point-of-care (PoC) microfluidic devices and biosensors, the LoaD platform has the potential to be reliable, sensitive, low-cost, and easy-to-use. The present global pandemic draws attention to the importance of rapid sample-to-answer PoC devices for minimising manual intervention and sample manipulation, thus increasing the safety of the health professional while minimising the chances of sample contamination. A biosensor is defined by its ability to measure an analyte by converting a biological binding event to tangible analytical data. With evolving manufacturing processes for both LoaDs and biosensors, it is becoming more feasible to embed biosensors within the platform and/or to pair the microfluidic cartridges with low-cost detection systems. This review considers the basics of the centrifugal microfluidics and describes recent developments in common biosensing methods and novel technologies for fluidic control and automation. Finally, an overview of current devices on the market is provided. This review will guide scientists who want to initiate research in LoaD PoC devices as well as providing valuable reference material to researchers active in the field.

Buoyancy-driven step emulsification on pneumatic centrifugal microfluidic platforms

We present here a new method for controlling the droplet size in step emulsification processes on a centrifugal microfluidic platform, which, in addition to the centrifugal force, uses pneumatic actuation for fluid displacement. We highlight the importance of the interplay between buoyancy effects and the flow rate at the step junction, and provide a simple analytical model relating these two quantities to the size of the droplets. Numerical models as well as experiments with water-in-oil emulsions are performed in support of the proposed model.

Detection of renal biomarkers in chronic kidney disease using microfluidics: progress, challenges and opportunities

Chronic kidney disease (CKD) typically evolves over many years in a latent period without clinical signs, posing key challenges to detection at relatively early stages of the disease. Accurate and timely diagnosis of CKD enable effective management of the disease and may prevent further progression. However, long turn-around times of current testing methods combined with their relatively high cost due to the need for established laboratory infrastructure, specialized instrumentation and trained personnel are drawbacks for efficient assessment and monitoring of CKD, especially in underserved and resource-poor locations. Among the emerging clinical laboratory approaches, microfluidic technology has gained increasing attention over the last two decades due to the possibility of miniaturizing bioanalytical assays and instrumentation, thus potentially improving diagnostic performance. In this article, we review current developments related to the detection of CKD biomarkers using microfluidics. A general trend in this emerging area is the search for novel, sensitive biomarkers for early detection of CKD using technology that is improved by means of microfluidics. It is anticipated that these innovative approaches will be soon adopted and utilized in both clinical and point-of-care settings, leading to improvements in life quality of patients.

Centrifugal microfluidic lab-on-a-chip system with automated sample lysis, DNA amplification and microarray hybridization for identification of enterohemorrhagic Escherichia coli culture isolates

Automated workflow that starts with a colony isolate and ends with a fluorescence signal on a DNA microarray.

Siphon-Induced Droplet Break-Off for Enhanced Mixing on a Centrifugal Platform

We present a powerful and compact batch-mode mixing and dilution technique for centrifugal microfluidic platforms. Siphon structures are designed to discretize continuous flows into a sequence of droplets of volumes as low as 100 nL. Using a passive, self-regulating 4-step mechanism, discrete volumes of two fluids are alternatingly issued into a common intermediate chamber. At its base, a capillary valve acts as a fluidic shift register; a single droplet is held in place while two or more droplets merge and pass through the capillary stop. These merged droplets are advectively mixed as they pass through the capillary valve and into the receiving chamber. Mixing is demonstrated for various combinations of liquids such as aqueous solutions as well as saline solutions and human plasma. The mixing quality is assessed on a quantitative scale by using a colorimetric method based on the mixing of potassium thiocyanate and iron(III) chloride, and in the case of human plasma using a spectroscopic method. For instance, volumes of 5 µL have been mixed in less than 20 s. Single-step dilutions up to 1:5 of plasma in a standard phosphate buffer solution are also demonstrated. This work describes the preliminary development of the mixing method which has since been integrated into a commercially available microfluidic cartridge.

Efficient Development of Integrated Lab-On-A-Chip Systems Featuring Operational Robustness and Manufacturability

The majority of commercially oriented microfluidic technologies provide novel point-of-use solutions for laboratory automation with important areas in the context of the life sciences such as health care, biopharma, veterinary medicine and agrifood as well as for monitoring of the environment, infrastructures and industrial processes. Such systems are often composed of a modular setup exhibiting an instrument accommodating rather conventional actuation, detection and control units which interfaces with a fluidically integrated "Lab-on-a-Chip" device handling (bio-)sample(s) and reagents. As the complex network of tiny channels, chambers and surface-functionalised zones can typically not be properly cleaned and regenerated, these microfluidic chips are mostly devised as single-use disposables. The availability of cost-efficient materials and associated structuring, functionalisation and assembly schemes thus represents a key ingredient along the commercialisation pipeline and will be a first focus of this work. Furthermore, and owing to their innate variability, investigations on biosamples mostly require the acquisition of statistically relevant datasets. Consequently, intermediate numbers of consistently performing chips are already needed during application development; to mitigate the potential pitfalls of technology migration and to facilitate regulatory compliance of the end products, manufacture of such pilot series should widely follow larger-scale production schemes. To expedite and de-risk the development of commercially relevant microfluidic systems towards high Technology Readiness Levels (TRLs), we illustrate a streamlined, manufacturing-centric platform approach employing the paradigms of tolerance-forgiving Design-for-Manufacture (DfM) and Readiness for Scale-up (RfS) from prototyping to intermediate pilot series and eventual mass fabrication. Learning from mature industries, we further propose pursuing a platform approach incorporating aspects of standardisation in terms of specification, design rules and testing methods for materials, components, interfaces, and operational procedures; this coherent strategy will foster the emergence of dedicated commercial supply chains and also improve the economic viability of Lab-on-a-Chip systems often targeting smaller niche markets by synergistically bundling technology development.

Review on pneumatic operations in centrifugal microfluidics

Centrifugal microfluidics allows for miniaturization, automation and parallelization of laboratory workflows. The fact that centrifugal forces are always directed radially outwards has been considered a main drawback for the implementation of complex workflows leading to the requirement of additional actuation forces for pumping, valving and switching. In this work, we review and discuss the combination of centrifugal with pneumatic forces which enables transport of even complex liquids in any direction on centrifugal systems, provides actuation for valving and switching, offers alternatives for mixing and enables accurate and precise metering and aliquoting. In addition, pneumatics can be employed for timing to carry out any of the above listed unit operations in a sequential and cascaded manner. Firstly, different methods to generate pneumatic pressures are discussed. Then, unit operations and applications that employ pneumatics are reviewed. Finally, a tutorial section discusses two examples to provide insight into the design process. The first tutorial explains a comparatively simple implementation of a pneumatic siphon valve and provides a workflow to derive optimum design parameters. The second tutorial discusses cascaded pneumatic operations consisting of temperature change rate actuated valving and subsequent pneumatic pumping. In conclusion, combining pneumatic actuation with centrifugal microfluidics allows for the design of robust fluidic networks with simple fluidic structures that are implemented in a monolithic fashion. No coatings are required and the overall demands on manufacturing are comparatively low. We see the combination of centrifugal forces with pneumatic actuation as a key enabling technology to facilitate compact and robust automation of biochemical analysis.

Programmable hydraulic resistor for microfluidic chips using electrogate arrays

Flow rates play an important role in microfluidic devices because they affect the transport of chemicals and determine where and when (bio)chemical reactions occur in these devices. Flow rates can conveniently be determined using external peripherals in active microfluidics. However, setting specific flow rates in passive microfluidics is a significant challenge because they are encoded on a design and fabrication level, leaving little freedom to users for adjusting flow rates for specific applications. Here, we present a programmable hydraulic resistor where an array of "electrogates" routes an incoming liquid through a set of resistors to modulate flow rates in microfluidic chips post-fabrication. This approach combines a battery-powered peripheral device with passive capillary-driven microfluidic chips for advanced flow rate control and measurement. We specifically show a programmable hydraulic resistor composed of 7 parallel resistors and 14 electrogates. A peripheral and smartphone application allow a user to activate selected electrogates and resistors, providing 127 (27-1) flow resistance combinations with values spanning on a 500 fold range. The electrogates feature a capillary pinning site (i.e. trench across the flow path) to stop a solution and an electrode, which can be activated in a few ms using a 3 V bias to resume flow based on electrowetting. The hydraulic resistor and microfluidic chip shown here enable flow rates from ~0.09 nL.s-1 up to ~5.66 nL.s-1 with the resistor occupying a footprint of only 15.8 mm2 on a 1 × 2 cm2 microfluidic chip fabricated in silicon. We illustrate how a programmable hydraulic resistor can be used to set flow rate conditions for laminar co-flow of 2 liquids and the enzymatic conversion of a substrate by stationary enzymes (alkaline phosphatase) downstream of the programmable hydraulic resistor.

Automated serial dilutions for high-dynamic-range assays enabled by fill-level-coupled valving in centrifugal microfluidics

We introduce a new concept for centrifugal microfluidics that enables fully automated serial dilution generation without any additional means besides temperature control. The key feature is time-independent, serial valving of mixing chambers by fill-level-coupled temperature change rate (FLC-TCR) actuated valving. The automated dilution is realized under continuous rotation which enables reliable control of wetting liquids without the need for any additional fabrication steps such as hydrophobic coating. All fluidic features are implemented in a monolithic fashion and disks are manufactured by foil thermoforming for scalable manufacturing. The new valving concept is demonstrated to reliably prevent valving if the diluted sample is not added to the mixing chamber (n = 30) and ensure valving if the dilution stage is completed (n = 15). The accuracy and precision of automated serial dilutions are verified by on-disk generation of qPCR standard curve dilutions and compared with manually generated reference dilutions. In a first step, the 5-log-stage standard curves are evaluated in a commercial qPCR thermocycler revealing a linearity of R2 ≥ 99.92% for the proposed LabDisk method vs. R2 ≥ 99.67% in manual reference dilutions. In a second step, the disk automated serial dilutions are combined with on-disk qPCR thermocycling and readout, both inside a LabDisk player. A 4-log-stage linearity of R2 ≥ 99.81% and a sensitivity of one leukemia associated ETV6-RUNX1 mutant DNA copy in a background of 100 000 wild-type DNA copies are achieved.

Extraction of nucleic acids from blood: unveiling the potential of active pneumatic pumping in centrifugal microfluidics for integration and automation of sample preparation processes

This paper describes the development of an on-chip nucleic acid (NA) extraction assay from whole blood using a centrifugal microfluidic platform that allows for pneumatic actuation of liquids during rotation. The combination of pneumatic and centrifugal forces makes it possible to perform fluidic operations without the need for integrating active control elements on the microfluidic cartridge. The cartridge is fabricated from thermoplastic polymers (e.g., Zeonor 1060R) and features a simple design that is compatible with injection molding. In addition, the cartridge is interfaced with two external vials for off-chip storage of the blood sample and retrieval of the eluted NA solution, respectively. On-chip capture of NAs is performed using an embedded solid-phase extraction matrix composed of commercial glass microfiber filters (Whatman GF/D and GF/F). The yield of the automated, on-chip extraction protocol, determined by measuring absorbance at 260 nm, is comparable to some of the best manually operated kits (e.g., Qiagen QIAamp DNA Mini Kit) while providing low assay-to-assay variability due to the high level of control provided by the platform for each processing step. The A260/A280 and A260/A230 ratios of the absorbance spectra also reveal that protein contamination of the sample is negligible. The capability of the pneumatic platform to circulate air flux through the microfluidic conduit was used to dry leftover ethanol residues retained in the capture matrix during washing. This method, applied in combination with localized heating, proved effective for reducing ethanol contamination in eluted samples from ∼12% to 1% (v/v).

Label-free, spatially multiplexed SPR detection of immunoassays on a highly integrated centrifugal Lab-on-a-Disc platform

As a direct, label-free method, Surface Plasmon Resonance (SPR) detection significantly reduces the needs for liquid handling and reagent storage compared to common enzyme-linked immunosorbent assays (ELISAs), thus enabling comprehensive multiplexing of bioassays on microfluidic sample-to-answer systems. This paper describes a highly integrated centrifugal Lab-on-a-Disc (LoaD) platform for automating the full process chain extending between plasma extraction and subsequent aliquoting to five parallelized reaction channels for quantitative SPR detection by an inexpensive smartphone camera. The entire, multi-step / multi-reagent operation completes within less than 1 h. While the emphasis of this work is on the fluidic automation and parallelization by previously introduced, very robust event-triggered valving and buoyancy-driven centripetal pumping schemes, we successfully implement an immunoglobulin G (IgG) assay; by specific functionalization of the detection surfaces, the same disc layout can readily be customised for immunoassays panels from whole blood.

Wirelessly powered and remotely controlled valve-array for highly multiplexed analytical assay automation on a centrifugal microfluidic platform

In this paper we present a wirelessly powered array of 128 centrifugo-pneumatic valves that can be thermally actuated on demand during spinning. The valves can either be triggered by a predefined protocol, wireless signal transmission via Bluetooth, or in response to a sensor monitoring a parameter like the temperature, or homogeneity of the dispersion. Upon activation of a resistive heater, a low-melting membrane (Parafilm™) is removed to vent an entrapped gas pocket, thus letting the incoming liquid wet an intermediate dissolvable film and thereby open the valve. The proposed system allows up to 12 heaters to be activated in parallel, with a response time below 3 s, potentially resulting in 128 actuated valves in under 30 s. We demonstrate, with three examples of common and standard procedures, how the proposed technology could become a powerful tool for implementing diagnostic assays on Lab-on-a-Disc. First, we implement wireless actuation of 64 valves during rotation in a freely programmable sequence, or upon user input in real time. Then, we show a closed-loop centrifugal flow control sequence for which the state of mixing of reagents, evaluated from stroboscopically recorded images, triggers the opening of the valves. In our last experiment, valving and closed-loop control are used to facilitate centrifugal processing of whole blood.

Label-free extraction of extracellular vesicles using centrifugal microfluidics

Extracellular vesicles (EVs) play an important role as active messengers in intercellular communication and distant microenvironment modeling. Increasingly, these EVs are recognized as important biomarkers for clinical diagnostics. However, current isolation methods of EVs are time-consuming and ineffective due to the high diffusive characteristics of nanoparticles coupled with fluid flow instability. Here, we develop a microfluidic CEntrifugal Nanoparticles Separation and Extraction (µCENSE) platform for the rapid and label-free isolation of microvesicles. By utilizing centrifugal microhydrodynamics, we subject the nanosuspensions between 100 nm and 1000 nm to a unique fluid flow resulting in a zonal separation into different outlets for easy post-processing. Our centrifugal platform utilizes a gentle and efficient size-based separation without the requirements of syringe pump and other accessories. Based on our results, we report a high separation efficiency of 90% and an extraction purity of 85% within a single platform. Importantly, we demonstrate high EV extraction using a table top centrifuge within a short duration of eight minutes. The simple processes and the small volume requirement further enhance the utility of the platform. With this platform, it serves as a potential for liquid biopsy extraction and point-of-care diagnostics.

Temperature change rate actuated bubble mixing for homogeneous rehydration of dry pre-stored reagents in centrifugal microfluidics

In centrifugal microfluidics, dead volumes in valves downstream of mixing chambers can hardly be avoided. These dead volumes are excluded from mixing processes and hence cause a concentration gradient. Here we present a new bubble mixing concept which avoids such dead volumes. The mixing concept employs heating to create a temperature change rate (TCR) induced overpressure in the air volume downstream of mixing chambers. The main feature is an air vent with a high fluidic resistance, representing a low pass filter with respect to pressure changes. Fast temperature increase causes rapid pressure increase in downstream structures pushing the liquid from downstream channels into the mixing chamber. As air further penetrates into the mixing chamber, bubbles form, ascend due to buoyancy and mix the liquid. Slow temperature/pressure changes equilibrate through the high fluidic resistance air vent enabling sequential heating/cooling cycles to repeat the mixing process. After mixing, a complete transfer of the reaction volume into the downstream fluidic structure is possible by a rapid cooling step triggering TCR actuated valving. The new mixing concept is applied to rehydrate reagents for loop-mediated isothermal amplification (LAMP). After mixing, the reaction mix is aliquoted into several reaction chambers for geometric multiplexing. As a measure for mixing efficiency, the mean coefficient of variation (C[combining macron]V[combining macron], n = 4 LabDisks) of the time to positivity (t_p) of the LAMP reactions (n = 11 replicates per LabDisk) is taken. The C[combining macron]V[combining macron] of the t_p is reduced from 18.5% (when using standard shake mode mixing) to 3.3% (when applying TCR actuated bubble mixing). The bubble mixer has been implemented in a monolithic fashion without the need for any additional actuation besides rotation and temperature control, which are needed anyhow for the assay workflow.

Comprehensive Study of the Flow Control Strategy in a Wirelessly Charged Centrifugal Microfluidic Platform with Two Rotation Axes

Centrifugal microfluidics has been widely applied in the sample-in-answer-out systems for the analyses of nucleic acids, proteins, and small molecules. However, the inherent characteristic of unidirectional fluid propulsion limits the flexibility of these fluidic chips. Providing an extra degree of freedom to allow the unconstrained and reversible pumping of liquid is an effective strategy to address this limitation. In this study, a wirelessly charged centrifugal microfluidic platform with two rotation axes has been constructed and the flow control strategy in such platform with two degrees of freedom was comprehensively studied for the first time. Inductively coupled coils are installed on the platform to achieve wireless power transfer to the spinning stage. A micro servo motor is mounted on both sides of the stage to alter the orientation of the device around a secondary rotation axis on demand during stage rotation. The basic liquid operations on this platform, including directional transport of liquid, valving, metering, and mixing, are comprehensively studied and realized. Finally, a chip for the simultaneous determination of hexavalent chromium [Cr(VI)] and methanal in water samples is designed and tested based on the strategy presented in this paper, demonstrating the potential use of this platform for on-site environmental monitoring, food safety testing, and other life science applications.

Motor-assisted chip-in-a-tube (MACT): a new 2- and 3-dimensional centrifugal microfluidic platform for biomedical applications

Currently, centrifuge apparatus is primarily an end-point sample processing piece of equipment. The lack of real-time active control has imposed an inherent limitation such that many delicate sample processing steps requiring immediate and accurate intervention have never been possible. We report herein a motor-assisted chip-in-a-tube (MACT) platform in which a microfluidic chip placed inside a common centrifuge canister can be rotated through wireless control in order to manipulate the centrifugal force vector in a 3-dimensional (3D) manner. As a demonstration experiment, we have used our MACT prototype to perform the operation for two common biomedical procedures, namely human blood plasma separation and E. coli plasmid DNA extraction. This simple, yet highly effective and versatile approach may serve as a generic one-for-all platform for a wide range of common laboratory experiments and bioassay applications.

Ultra-rapid and low-cost fabrication of centrifugal microfluidic platforms with active mechanical valves

Fabrication of microfluidic discs with mechanical active valves by a cutter plotter.

The Effect of Moment of Inertia on the Liquids in Centrifugal Microfluidics

The flow of liquids in centrifugal microfluidics is unidirectional and dominated by centrifugal and Coriolis forces (i.e., effective only at T-junctions). Developing mechanisms and discovering efficient techniques to propel liquids in any direction other than the direction of the centrifugal force has been the subject of a large number of studies. The capillary force attained by specific surface treatments, pneumatic energy, active and passive flow reciprocation and Euler force have been previously introduced in order to manipulate the liquid flow and push it against the centrifugal force. Here, as a new method, the moment of inertia of the liquid inside a chamber in a centrifugal microfluidic platform is employed to manipulate the flow and propel the liquid passively towards the disc center. Furthermore, the effect of the moment of inertia on the liquid in a rectangular chamber is evaluated, both in theory and experiments, and the optimum geometry is defined. As an application of the introduced method, the moment of inertia of the liquid is used in order to mix two different dyed deionized (DI) waters; the mixing efficiency is evaluated and compared to similar mixing techniques. The results show the potential of the presented method for pumping liquids radially inward with relatively high flow rates (up to 23 mm³/s) and also efficient mixing in centrifugal microfluidic platforms.