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

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.

Microfluidic systems for infectious disease diagnostics

Microorganisms, encompassing both uni- and multicellular entities, exhibit remarkable diversity as omnipresent life forms in nature. They play a pivotal role by supplying essential components for sustaining biological processes across diverse ecosystems, including higher host organisms. The complex interactions within the human gut microbiota are crucial for metabolic functions, immune responses, and biochemical signalling, particularly through the gut-brain axis. Viruses also play important roles in biological processes, for example by increasing genetic diversity through horizontal gene transfer when replicating inside living cells. On the other hand, infection of the human body by microbiological agents may lead to severe physiological disorders and diseases. Infectious diseases pose a significant burden on global healthcare systems, characterized by substantial variations in the epidemiological landscape. Fast spreading antibiotic resistance or uncontrolled outbreaks of communicable diseases are major challenges at present. Furthermore, delivering field-proven point-of-care diagnostic tools to the most severely affected populations in low-resource settings is particularly important and challenging. New paradigms and technological approaches enabling rapid and informed disease management need to be implemented. In this respect, infectious disease diagnostics taking advantage of microfluidic systems combined with integrated biosensor-based pathogen detection offers a host of innovative and promising solutions. In this review, we aim to outline recent activities and progress in the development of microfluidic diagnostic tools. Our literature research mainly covers the last 5 years. We will follow a classification scheme based on the human body systems primarily involved at the clinical level or on specific pathogen transmission modes. Important diseases, such as tuberculosis and malaria, will be addressed more extensively.

Programmable fluidic networks on centrifugal microfluidic discs

BACKGROUND

Biomedical diagnostic and lab automation solutions built on the Lab-on-a-Disc (LoaD) platform has great potential due to their independence from specialised micro-pumps and their ease of integration, through direct pipetting, with manual or automated workflows. However, a challenge for all microfluidic chips is their cost of manufacture when each microfluidic disc must be customized for a specific application. In this paper, we present centrifugal discs with programmable fluidic networks.

RESULTS

Based on dissolvable film valves, we present two technologies. The first, based on recently introduced pulse-actuated dissolvable film valves, is a centrifugal disc which, depending on how it is loaded, is configured to perform either six sequential reagent releases through one reaction chamber or three sequential reagent releases through two reaction chambers. In the second approach, we use the previously introduced electronic Lab-on-a-Disc (eLoaD) wireless valve array, which can actuate up to 128 centrifugo-pneumatic dissolvable film valves in a pre-defined sequence. In this approach we present a disc which can deliver any one of 8 reagent washes to any one of four reaction chambers. We use identical discs to demonstrate the first four sequential washes through two reaction chambers and then two sequential washes through four reaction chambers.

SIGNIFICANCE

These programmable fluidic networks have the potential to allow a single disc architecture to be applied to multiple different assay types and so can offer a lower-cost and more integrated alternative to the standard combination of micro-titre plate and liquid handling robot. Indeed, it may even be possible to conduct multiple different assays concurrently. This can have the effect of reducing manufacturing costs and streamlining supply-chains and so results in a more accessible diagnostic platform.

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 solid phase DNA extraction on a lab-on-a-disc with two-degrees of freedom instrumentation

BACKGROUND

Lab-on-a-disc (LoaD) technology has emerged as a transformative approach for point-of-care diagnostics and high-throughput testing. The promise of integrating multiple laboratory functions onto a single integrated platform has significant implications for healthcare, especially in resource-limited settings. However, one of the primary challenges faced in the design and manufacture of LoaD devices is the integration of effective valving mechanisms. These valves are essential for fluid control and routing, but their intricacy often leads to complexities in design and increased vulnerability to failure. This emphasizes the need for improved designs and manufacturing processes without complex, integrated valving mechanisms. (96) RESULTS: We describe a fully automated biological workflow and reagent actuation on a LoaD device without an integrated valving system. The Two Degrees-of-Freedom (2DoF) custom centrifuge alters the centre of rotation, facilitating fluid flow direction changes on the microfluidic platform through a custom programmed interface. A novel 360-degree fluid manipulation approach via secondary planetary gear motion enabled sequential assay reagent actuation without embedded valve triggering, with the addition of infinite incubation times and efficient use of platform realty. The simplified LoaD platform uses clever design, with intermediate flow chambers to avoid cross contamination between reagent steps. Notably, the optimized LoaD platform demonstrated a two-fold DNA yield at higher HEK-293 cell concentrations compared to commercially available spin-column kits. This significantly simplified LoaD platform successfully automated a common, complex workflow without inhibiting DNA purification. (129) SIGNIFICANCE: This system exhibits the clever coupling of both 2DoF and centrifugal microfluidics to create an autonomous testing package capable of eradicating the need for complex valving systems to automate biological workflows on LoaDs. This automated system has outperformed commercially available DNA extraction kits for higher cell counts. The platform's elimination of valve requirements ensures unlimited sample incubation times and enhances reliability, making it a straightforward option for automated biological workflows, particularly in diagnostics. (73).

Sample-to-answer sensing technologies for nucleic acid preparation and detection in the field

Efficient sample preparation and accurate disease diagnosis under field conditions are of great importance for the early intervention of diseases in humans, animals, and plants. However, in-field preparation of high-quality nucleic acids from various specimens for downstream analyses, such as amplification and sequencing, is challenging. Thus, developing and adapting sample lysis and nucleic acid extraction protocols suitable for portable formats have drawn significant attention. Similarly, various nucleic acid amplification techniques and detection methods have also been explored. Combining these functions in an integrated platform has resulted in emergent sample-to-answer sensing systems that allow effective disease detection and analyses outside a laboratory. Such devices have a vast potential to improve healthcare in resource-limited settings, low-cost and distributed surveillance of diseases in food and agriculture industries, environmental monitoring, and defense against biological warfare and terrorism. This paper reviews recent advances in portable sample preparation technologies and facile detection methods that have been / or could be adopted into novel sample-to-answer devices. In addition, recent developments and challenges of commercial kits and devices targeting on-site diagnosis of various plant diseases are discussed.

Point-of-Care Devices for Viral Detection: COVID-19 Pandemic and Beyond

The pandemic of COVID-19 and its widespread transmission have made us realize the importance of early, quick diagnostic tests for facilitating effective cure and management. The primary obstacles encountered were accurately distinguishing COVID-19 from other illnesses including the flu, common cold, etc. While the polymerase chain reaction technique is a robust technique for the determination of SARS-CoV-2 in patients of COVID-19, there arises a high demand for affordable, quick, user-friendly, and precise point-of-care (POC) diagnostic in therapeutic settings. The necessity for available tests with rapid outcomes spurred the advancement of POC tests that are characterized by speed, automation, and high precision and accuracy. Paper-based POC devices have gained increasing interest in recent years because of rapid, low-cost detection without requiring external instruments. At present, microfluidic paper-based analysis devices have garnered public attention and accelerated the development of such POCT for efficient multistep assays. In the current review, our focus will be on the fabrication of detection modules for SARS-CoV-2. Here, we have included a discussion on various strategies for the detection of viral moieties. The compilation of these strategies would offer comprehensive insight into the detection of the causative agent preparedness for future pandemics. We also provide a descriptive outline for paper-based diagnostic platforms, involving the determination mechanisms, as well as a commercial kit for COVID-19 as well as their outlook.

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.

Extremely Precise Blood-Plasma Separation from Whole Blood on a Centrifugal Microfluidic Disk (Lab-on-a-Disk) Using Separator Gel

Due to the expansion of point-of-care devices, proposing a convenient and efficient method for blood-plasma separation would help with the use of point-of-care devices. Commercial microfluidic chips are only able to separate a limited amount of plasma, and the majority of these chips need an active valve system, which leads to increase manufacturing cost and complexity. In this research study, we designed a centrifugal microfluidic disk with a passive valve for ultra-accurate and efficient blood-plasma separation on a large scale (2-3 mL). The disk contained a separator gel, which, after applying the centrifugal force, separated the plasma and red blood cells. The passive valve worked based on the inertial force and was able to transfer more than 90% of the separated plasma to the next chamber. The results demonstrated that the separated plasma was 99.992% pure. This study compared the efficiency of the disk containing separating gel with the common lab-on-a-disk design for plasma separation. A comparison of the results showed that although the common lab-on-a-disk design could separate almost pure plasma as the disk contained separator gel, it could only transfer 60% of plasma to the next chamber.

Microfluidics-Based POCT for SARS-CoV-2 Diagnostics

A microfluidic chip is a tiny reactor that can confine and flow a specific amount of fluid into channels of tens to thousands of microns as needed and can precisely control fluid flow, pressure, temperature, etc. Point-of-care testing (POCT) requires small equipment, has short testing cycles, and controls the process, allowing single or multiple laboratory facilities to simultaneously analyze biological samples and diagnose infectious diseases. In general, rapid detection and stage assessment of viral epidemics are essential to overcome pandemic situations and diagnose promptly. Therefore, combining microfluidic devices with POCT improves detection efficiency and convenience for viral disease SARS-CoV-2. At the same time, the POCT of microfluidic chips increases user accessibility, improves accuracy and sensitivity, shortens detection time, etc., which are beneficial in detecting SARS-CoV-2. This review shares recent advances in POCT-based testing for COVID-19 and how it is better suited to help diagnose in response to the ongoing pandemic.

Enhancing Mixing Performance in a Rotating Disk Mixing Chamber: A Quantitative Investigation of the Effect of Euler and Coriolis Forces

Lab-on-a-CD (LOCD) is gaining importance as a diagnostic platform due to being low-cost, easy-to-use, and portable. During LOCD usage, mixing and reaction are two processes that play an essential role in biochemical applications such as point-of-care diagnosis. In this paper, we numerically and experimentally investigate the effects of the Coriolis and Euler forces in the mixing chamber during the acceleration and deceleration of a rotating disk. The mixing performance is investigated under various conditions that have not been reported, such as rotational condition, chamber aspect ratio at a constant volume, and obstacle arrangement in the chamber. During disk acceleration and deceleration, the Euler force difference in the radial direction causes rotating flows, while the Coriolis force induces perpendicular vortices. Increasing the maximum rotational velocity improves the maximum rotational displacement, resulting in better mixing performance. A longer rotational period increases the interfacial area between solutions and enhances mixing. Mixing performance also improves when there is a substantial difference between Euler forces at the inner and outer radii. Furthermore, adding obstacles in the angular direction also passively promotes or inhibits mixing by configuration. This quantitative investigation provides valuable information for designing and developing high throughput and multiplexed point-of-care LOCDs.

Autonomous electrochemical biosensing of glial fibrillary acidic protein for point-of-care detection of central nervous system injuries

The integration of electrochemical biosensors into fluid handling units such as paper-based, centrifugal, and capillary microfluidic devices has been explored with the purpose of developing point-of-care platforms for quantitative detection of bodily fluid markers. However, the present fluidic device designs largely lack the capacity of full assay automation, needing manual loading of one or multiple reagents or requiring external devices for liquid manipulation. Such fluidic handing platforms also require universality for detecting various biomarkers. These platforms are also largely produced using materials unsuitable for scalable manufacturing and with a high production cost. The mechanism of fluid flow also often induces noise to the embedded biosensors which adversely impacts the accuracy of biosensing. This work addresses these challenges by presenting a reliable design of a fully automated and universal capillary-driven microfluidic platform that automates several steps of label-free electrochemical biosensing assays. These steps include sample aliquoting, controlled incubation, removal of non-specific bindings, reagent mixing and delivery to sensing electrodes, and electrochemical detection. The multilayer architecture of the microfluidic device is made of polymeric and adhesive materials commercially used for the fabrication of point-of-care devices. The design and geometry of different components of the device (e.g., sampling unit, mixer, resistances, delay valves, interconnecting components) were optimized using a combined experimental testing and numerical fluid flow modeling to reach high reproducibility and minimize the noise-induced to the biosensor. As a proof of concept, the performance of this on-chip immunosensing platform was demonstrated for rapid and autonomous detection of glial fibrillary acidic proteins (GFAP) in phosphate-buffered saline (PBS). The microfluidic immunosensing device exhibited a linear detection range of 10-1000 pg mL^-1 for the detection of GFAP within 30 min, with a limit of detection (LoD) and sensitivity of 3 pg mL^-1 and 39 mL pg^-1 mm^-2 in PBS, respectively. Owing to its simplicity, sample-to-result performance, universality for handing different biofluids, low cost, high reproducibility, compatibility with scalable production, and short analysis time, the proposed biosensing platform can be further adapted for the detection of other biomarkers in different clinical bodily fluids for rapid diagnostic and prognostic applications.

Design and fabrication of a low-cost wireless camera imaging system for centrifugal microfluidics

Centrifugal microfluidic devices offer a robust method for low-volume fluid handling by combining low-cost instrumentation with highly integrated automation. Crucial to the efficacy of Lab-on-a-Disc (LoaD) device operation is the selection of robust valving technology, the design of on-disc fluidic structures, and accurate control of disc spin-speeds (centrifugal force) during operation. The design and refinement of fluidic and valving structures is often guided by inspecting disc operation using high-speed camera systems. This approach involves synchronising image acquisition with disc rotation to visualise liquid flow through a series of images often presented in a video format. Depending on the decisions taken, such systems can cost from €4,000 upwards. This paper outlines the development of a low-cost centrifugal test-stand with an integrated imaging system using a generic wireless camera to record videos directly to a smartphone device. This imaging system can be fabricated using only 3D printers and a low-cost CNC milling machine from widely available materials for approximately €350. High-fidelity imaging of the entire disc for flow visualisation and the recording of real-time colour intensity measurements are facilitated by this standalone device. A vibration analysis study has been performed to determine the rotational velocity range at which the system can be safely operated. Furthermore, the efficacy of the imaging system has been demonstrated by performing real-time colour intensity measurements of dyed water dilutions.

Perspectives in translating microfluidic devices from laboratory prototyping into scale-up production

Transforming lab research into a sustainable business is becoming a trend in the microfluidic field. However, there are various challenges during the translation process due to the gaps between academia and industry, especially from laboratory prototyping to industrial scale-up production, which is critical for potential commercialization. In this Perspective, based on our experience in collaboration with stakeholders, e.g., biologists, microfluidic engineers, diagnostic specialists, and manufacturers, we aim to share our understanding of the manufacturing process chain of microfluidic cartridge from concept development and laboratory prototyping to scale-up production, where the scale-up production of commercial microfluidic cartridges is highlighted. Four suggestions from the aspect of cartridge design for manufacturing, professional involvement, material selection, and standardization are provided in order to help scientists from the laboratory to bring their innovations into pre-clinical, clinical, and mass production and improve the manufacturability of laboratory prototypes toward commercialization.

Monolithic, 3D-printed lab-on-disc platform for multiplexed molecular detection of SARS-CoV-2

Multiplexed detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rather than detection targeting a single gene is crucial to ensure more accurate coronavirus disease 2019 (COVID-19) diagnostics. Here, we develop a monolithic, 3D-printed, lab-on-disc platform for multiplexed molecular detection of SARS-CoV-2. The centrifugal lab-on-disc is fabricated in one step using simple 3D printing technology, circumventing the need for aligning and binding multiple layers. By combining isothermal amplification technology, this lab-on-disc platform is capable of simultaneously detecting the nucleoprotein and envelope genes of SARS-CoV-2 as well as an internal control of the human POP7 gene. Within a 50-minute incubation period, 100 copies SARS-CoV-2 RNA can be detected through visual observation according to color and fluorescence changes in the disc. Further, we clinically validated the lab-on-disc platform by testing 20 nasopharyngeal swab samples and demonstrated a sensitivity of 100% and an accuracy of 95%. Therefore, the monolithic, 3D-printed, lab-on-disc platform provides simple, rapid, disposable, sensitive, reliable, and multiplexed molecular detection of SARS-CoV-2, holding promise for COVID-19 diagnostics at the point of care.

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.

Lab-on-a-disc for ultrafast plasmonic assay of cysteamine

Cysteamine (CA) is a cystine depleting agent used in the treatment of cystinosis and many other diseases. However, high dose of CA can be toxic and thus point-of-care-test devices measuring blood CA level can be highly beneficial. Here, we report a highly sensitive, straightforward, and quantitative assay for the colorimetric and spectroscopic determination of CA concentration using plasmonic nanoparticles. The principle is based on the chemical etching-induced exchange of the surface ligands of plasmonic gold nanoparticles (AuNPs) upon the addition of CA. Moreover, destabilized particles can aggregate to generate the plasmonic couplings that trigger the redshift in the ultraviolet-visible (UV-vis) spectrum (the absorption band shifted from 526 to 732 nm) and the solution color change (wine-red to blackish-blue). This plasmonic AuNPs sensor displays a clear red-to-blue colorimetric transition in the presence of CA among various biothiols with high specificity and sensitivity within a short time (<15 s). Furthermore, a lab-on-a-disc platform was applied to the analysis of blood samples donated by healthy volunteers spiked with known amounts of the CA standard solution. This fully automated lab-on-a-disc platform approach for naked eye detecting the CA concentration in human blood samples (20 μL) is highly simple and time-efficient (<6 min), and it would be potentially useful for the careful selection of CA doses in the hospital industry.

Design Optimization of Centrifugal Microfluidic “Lab-on-a-Disc” Systems towards Fluidic Larger-Scale Integration

Enhancing the degree of functional multiplexing while assuring operational reliability and manufacturability at competitive costs are crucial ingredients for enabling comprehensive sample-to-answer automation, e.g., for use in common, decentralized “Point-of-Care” or “Point-of-Use” scenarios. This paper demonstrates a model-based “digital twin” approach, which efficiently supports the algorithmic design optimization of exemplary centrifugo-pneumatic (CP) dissolvable-film (DF) siphon valves toward larger-scale integration (LSI) of well-established “Lab-on-a-Disc” (LoaD) systems. Obviously, the spatial footprint of the valves and their upstream laboratory unit operations (LUOs) have to fit, at a given radial position prescribed by its occurrence in the assay protocol, into the locally accessible disc space. At the same time, the retention rate of a rotationally actuated CP-DF siphon valve and, most challengingly, its band width related to unavoidable tolerances of experimental input parameters need to slot into a defined interval of the practically allowed frequency envelope. To accomplish particular design goals, a set of parametrized metrics is defined, which are to be met within their practical boundaries while (numerically) minimizing the band width in the frequency domain. While each LSI scenario needs to be addressed individually on the basis of the digital twin, a suite of qualitative design rules and instructive showcases structures are presented.

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.

Special Issue on “Advances in Microfluidics Technology for Diagnostics and Detection”

In recent years microfluidics and lab-on-a-chip havecome to the forefront in diagnostics and detection [...]

Point-of-care diagnostics for infectious diseases: From methods to devices

The current widespread of COVID-19 all over the world, which is caused by SARS-CoV-2 virus, has again emphasized the importance of development of point-of-care (POC) diagnostics for timely prevention and control of the pandemic. Compared with labor- and time-consuming traditional diagnostic methods, POC diagnostics exhibit several advantages such as faster diagnostic speed, better sensitivity and specificity, lower cost, higher efficiency and ability of on-site detection. To achieve POC diagnostics, developing POC detection methods and correlated POC devices is the key and should be given top priority. The fast development of microfluidics, micro electro-mechanical systems (MEMS) technology, nanotechnology and materials science, have benefited the production of a series of portable, miniaturized, low cost and highly integrated POC devices for POC diagnostics of various infectious diseases. In this review, various POC detection methods for the diagnosis of infectious diseases, including electrochemical biosensors, fluorescence biosensors, surface-enhanced Raman scattering (SERS)-based biosensors, colorimetric biosensors, chemiluminiscence biosensors, surface plasmon resonance (SPR)-based biosensors, and magnetic biosensors, were first summarized. Then, recent progresses in the development of POC devices including lab-on-a-chip (LOC) devices, lab-on-a-disc (LOAD) devices, microfluidic paper-based analytical devices (μPADs), lateral flow devices, miniaturized PCR devices, and isothermal nucleic acid amplification (INAA) devices, were systematically discussed. Finally, the challenges and future perspectives for the design and development of POC detection methods and correlated devices were presented. The ultimate goal of this review is to provide new insights and directions for the future development of POC diagnostics for the management of infectious diseases and contribute to the prevention and control of infectious pandemics like COVID-19.

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

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