Pulling-Force Spinning Top for Serum Separation Combined with Paper-Based Microfluidic Devices in COVID-19 ELISA Diagnosis

Paper-Based Microfluidic Analytical Device Patterned by Label Printer for Point-of-Care Blood Glucose and Hematocrit Detection Using 3D-Printed Smartphone Cassette

This study presents a portable, low-cost, point-of-care (POC) system for the simultaneous detection of blood glucose and hematocrit. The system consists of a disposable origami microfluidic paper-based analytical device (μPAD) for plasma separation, filtration, and reaction functions and a 3D-printed cassette for hematocrit and blood glucose detection using a smartphone. The origami μPAD is patterned using a cost-effective label printing technique instead of the conventional wax printing method. The 3D-printed cassette incorporates an array of LED lights, which mitigates the effects of intensity variations in the ambient light and hence improves the accuracy of the blood glucose and hematocrit concentration measurements. The hematocrit concentration is determined quantitatively by measuring the distance of plasma wicking along the upper layer of the origami μPAD, which is pretreated with sodium chloride and Tween 20 to induce dehydration and aggregation of the red blood cells. The filtered plasma also penetrates to the lower layer of the origami μPAD, where it reacts with embedded colorimetric assay reagents to produce a yellowish-brown complex. A color image of the reaction complex is captured using a smartphone inserted into the 3D-printed cassette. The image is analyzed using self-written RGB software to quantify the blood glucose concentration. The calibration results indicate that the proposed detection platform provides an accurate assessment of the blood glucose level over the range of 45-630 mg/dL (R2 = 0.9958). The practical feasibility of the proposed platform is demonstrated by measuring the blood glucose and hematocrit concentrations in 13 human whole blood samples. Taking the measurements obtained from commercial glucose and hematocrit meters as a benchmark, the proposed system has a differential of no more than 6.4% for blood glucose detection and 9.1% for hematocrit detection. Overall, the results confirm that the proposed μPAD is a promising solution for cost-effective and reliable POC health monitoring.

Open and closed microfluidics for biosensing

Biosensing is vital for many areas like disease diagnosis, infectious disease prevention, and point-of-care monitoring. Microfluidics has been evidenced to be a powerful tool for biosensing via integrating biological detection processes into a palm-size chip. Based on the chip structure, microfluidics has two subdivision types: open microfluidics and closed microfluidics, whose operation methods would be diverse. In this review, we summarize fundamentals, liquid control methods, and applications of open and closed microfluidics separately, point out the bottlenecks, and propose potential directions of microfluidics-based biosensing.

Engineered two-dimensional nanomaterials based diagnostics integrated with internet of medical things (IoMT) for COVID-19

More than four years have passed since an inimitable coronavirus disease (COVID-19) pandemic hit the globe in 2019 after an uncontrolled transmission of the severe acute respiratory syndrome (SARS-CoV-2) infection. The occurrence of this highly contagious respiratory infectious disease led to chaos and mortality all over the world. The peak paradigm shift of the researchers was inclined towards the accurate and rapid detection of diseases. Since 2019, there has been a boost in the diagnostics of COVID-19 via numerous conventional diagnostic tools like RT-PCR, ELISA, etc., and advanced biosensing kits like LFIA, etc. For the same reason, the use of nanotechnology and two-dimensional nanomaterials (2DNMs) has aided in the fabrication of efficient diagnostic tools to combat COVID-19. This article discusses the engineering techniques utilized for fabricating chemically active E2DNMs that are exceptionally thin and irregular. The techniques encompass the introduction of heteroatoms, intercalation of ions, and the design of strain and defects. E2DNMs possess unique characteristics, including a substantial surface area and controllable electrical, optical, and bioactive properties. These characteristics enable the development of sophisticated diagnostic platforms for real-time biosensors with exceptional sensitivity in detecting SARS-CoV-2. Integrating the Internet of Medical Things (IoMT) with these E2DNMs-based advanced diagnostics has led to the development of portable, real-time, scalable, more accurate, and cost-effective SARS-CoV-2 diagnostic platforms. These diagnostic platforms have the potential to revolutionize SARS-CoV-2 diagnosis by making it faster, easier, and more accessible to people worldwide, thus making them ideal for resource-limited settings. These advanced IoMT diagnostic platforms may help with combating SARS-CoV-2 as well as tracking and predicting the spread of future pandemics, ultimately saving lives and mitigating their impact on global health systems.

Low-Cost Biosensor Technologies for Rapid Detection of COVID-19 and Future Pandemics

Many systems have been designed for the detection of SARS-CoV-2, which is the virus that causes COVID-19. SARS-CoV-2 is readily transmitted, resulting in the rapid spread of disease in human populations. Frequent testing at the point of care (POC) is a key aspect for controlling outbreaks caused by SARS-CoV-2 and other emerging pathogens, as the early identification of infected individuals can then be followed by appropriate measures of isolation or treatment, maximizing the chances of recovery and preventing infectious spread. Diagnostic tools used for high-frequency testing should be inexpensive, provide a rapid diagnostic response without sophisticated equipment, and be amenable to manufacturing on a large scale. The application of these devices should enable large-scale data collection, help control viral transmission, and prevent disease propagation. Here we review functional nanomaterial-based optical and electrochemical biosensors for accessible POC testing for COVID-19. These biosensors incorporate nanomaterials coupled with paper-based analytical devices and other inexpensive substrates, traditional lateral flow technology (antigen and antibody immunoassays), and innovative biosensing methods. We critically discuss the advantages and disadvantages of nanobiosensor-based approaches compared to widely used technologies such as PCR, ELISA, and LAMP. Moreover, we delineate the main technological, (bio)chemical, translational, and regulatory challenges associated with developing functional and reliable biosensors, which have prevented their translation into the clinic. Finally, we highlight how nanobiosensors, given their unique advantages over existing diagnostic tests, may help in future pandemics.

A portable multi-channel fluorescent paper-based microfluidic chip based on smartphone imaging for simultaneous detection of four heavy metals

Due to the excessive contamination of heavy metals pollution, it is very urgent and necessary to develop a real-time detection method for the heavy metals in food. As a target sensing device, a paper-based microfluidic device (μPAD) has the advantages of simplicity, low-cost, and portability. In this study, a self-driven microfluidic paper-based chip was first developed for the simultaneous detection of four targets. The channels on the microfluidic chip were prepared by using wax printing and automatic screen printing on the filter paper, where liquid flowed by capillary force without pump assistance. Based on the specific binding ability of aptamers to heavy metals, a "turn-on" fluorescence aptasensor for the simultaneous detection of four heavy metal ions was developed on the proposed multi-channel device via smartphone imaging. The obtained fluorescence images were digitized into RGB color values by Image J software, and an M-mode was established to realize the quantitative detection of heavy metal ions. Under optimal conditions, the limits of detection for lead(II), mercury(II), cadmium(II), and arsenic(III) were 4.20 nM, 1.70 nM, 2.04 nM, and 1.65 nM, respectively. Furthermore, the aptasensor was successfully applied to the quantitative detection of four heavy metal ions in apple and lettuce samples with recovery rates of 84.0%-104.1%.

Recent advances in point-of-care testing of COVID-19

Advances in microfluidic device miniaturization and system integration contribute to the development of portable, handheld, and smartphone-compatible devices. These advancements in diagnostics have the potential to revolutionize the approach to detect and respond to future pandemics. Accordingly, herein, recent advances in point-of-care testing (POCT) of coronavirus disease 2019 (COVID-19) using various microdevices, including lateral flow assay strips, vertical flow assay strips, microfluidic channels, and paper-based microfluidic devices, are reviewed. However, visual determination of the diagnostic results using only microdevices leads to many false-negative results due to the limited detection sensitivities of these devices. Several POCT systems comprising microdevices integrated with portable optical readers have been developed to address this issue. Since the outbreak of COVID-19, effective POCT strategies for COVID-19 based on optical detection methods have been established. They can be categorized into fluorescence, surface-enhanced Raman scattering, surface plasmon resonance spectroscopy, and wearable sensing. We introduced next-generation pandemic sensing methods incorporating artificial intelligence that can be used to meet global health needs in the future. Additionally, we have discussed appropriate responses of various testing devices to emerging infectious diseases and prospective preventive measures for the post-pandemic era. We believe that this review will be helpful for preparing for future infectious disease outbreaks.

An electrochemical molecularly imprinted microfluidic paper-based chip for detection of inflammatory biomarkers IL-6 and PCT

Based on surface biomolecular imprinting technology, a rotary microfluidic electrochemical paper-based chip (MIP-ePADs) was proposed for sensitive and selective detection of human interleukin 6 (IL-6) and procalcitonin (PCT). Compared with the traditional method, the sample can be added directly on the MIP-ePAD by rotating the working electrode, which avoids the loss of the liquid to be tested and greatly simplifies the process of electropolymerization imprinting and template elution. Our experimental results show that linear concentration ranges of IL-6 and PCT in the electrochemical molecularly imprinted microfluidic paper-based chip ranged from 0.01 to 5 ng mL-1, with their detection limits being 3.5 and 2.1 pg mL-1, respectively. For the detection of actual serum samples, there was no significant difference between the results of MIP-ePADs and the traditional electrochemiluminescence method used in hospitals, indicating that the paper-based chip can be used for stable and accurate analysis and detection. The chip greatly reduces the cost of clinical trials due to its advantages of easy preparation and low cost. The chip can be used for the analysis of non-antibody inflammation markers and can be widely used in home and hospital treatment detection. This method will not only play an important role in rapid detection, but also provide new ideas for the improvement of rapid detection technology.

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.

Diagnostics and analysis of SARS-CoV-2: current status, recent advances, challenges and perspectives

The disastrous spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has induced severe public healthcare issues and weakened the global economy significantly. Although SARS-CoV-2 infection is not as fatal as the initial outbreak, many infected victims suffer from long COVID. Therefore, rapid and large-scale testing is critical in managing patients and alleviating its transmission. Herein, we review the recent advances in techniques to detect SARS-CoV-2. The sensing principles are detailed together with their application domains and analytical performances. In addition, the advantages and limits of each method are discussed and analyzed. Besides molecular diagnostics and antigen and antibody tests, we also review neutralizing antibodies and emerging SARS-CoV-2 variants. Further, the characteristics of the mutational locations in the different variants with epidemiological features are summarized. Finally, the challenges and possible strategies are prospected to develop new assays to meet different diagnostic needs. Thus, this comprehensive and systematic review of SARS-CoV-2 detection technologies may provide insightful guidance and direction for developing tools for the diagnosis and analysis of SARS-CoV-2 to support public healthcare and effective long-term pandemic management and control.

Development of Novel Paper-Based Assay for Direct Serum Separation

Background: Many conventional laboratory tests require serum separation using a clot activator/gel tube, followed by centrifugation in an equipped laboratory. The aim of this study is development of novel, equipment-free, paper-based assay for direct and efficient serum separation. Methods: Fresh blood was directly applied to wax-channeled filter paper treated with clotting activator/s and then observed for serum separation. The purity, efficiency, recovery, reproducibility, and applicability of the assay were validated after optimization. Results: Serum was successfully separated using activated partial thromboplastin time (APTT) reagent and calcium chloride-treated wax-channeled filter paper within 2 min. The assay was optimized using different coagulation activators, paper types, blood collection methods, and incubation conditions. Confirmation of serum separation from cellular components was achieved by direct visualization of the yellow serum band, microscopic imaging of the pure serum band, and absence of blood cells in recovered serum samples. Successful clotting was evaluated by the absence of clotting of recovered serum by prolonged prothrombin time and APTT, absence of fibrin degradation products, and absence of Staphylococcus aureus-induced coagulation. Absence of hemolysis was confirmed by undetectable hemoglobin from recovered serum bands. The applicability of serum separated in paper was tested directly by positive color change on paper using bicinchoninic acid protein reagent, on recovered serum samples treated with Biuret and Bradford reagents in tubes, or measurement of thyroid-stimulating hormone and urea compared to standard serum samples. Serum was separated using the paper-based assay from 40 voluntary donors and from the same donor for 15 days to confirm reproducibility. Dryness of coagulants in paper prevents serum separation that can be re-stored by a re-wetting step. Conclusions: Paper-based serum separation allows for development of sample-to-answer paper-based point-of-care tests or simple and direct blood sampling for routine diagnostic tests.

Alternative platform for COVID-19 diagnosis based on AuNP-modified lab-on-paper

COVID-19 has caused global health problems, and so rapid diagnosis is crucial to slow spread of the disease. Herein, a novel lab-on-paper screening method for SARS-CoV-2 Omicron BA.2 variant was developed using a gold nanoparticle-based colorimetric biosensor along with sensitive detection of SARS-CoV-2 antigen using laser desorption ionization-mass spectrometry (LDI-MS). As a result of antigen-antibody interaction, in the presence of SARS-CoV-2 antigen the gold nanoparticles undergo aggregation and change color from red to light purple, allowing for rapid determination of SARS-CoV-2 antigen with the naked eye. Furthermore, the lab-on-paper method can be directly applied as a substrate for sensitive quantitation of SARS-CoV-2 antigen in saliva using LDI-MS without the use of a conventional organic matrix and sample preparation. LDI-MS offers early diagnosis with high sensitivity, rapidity without sample preparation and lower cost per test compared with reverse transcriptase-PCR, which is crucial for preventing mortality in patients with underlying conditions. This method showed linearity over 0.01-1 μg mL^-1 covering the cut-off value of 0.048 μg mL^-1 for COVID-19 detection in human saliva. Moreover, a colorimetric sensor for urea was also fabricated in-parallel, for prediction of COVID-19 severity in patients with chronic kidney disease. The color change upon increasing urea concentration directly reflected kidney damage, which is related to increasing risk of mortality among patients with COVID-19. Hence, this platform might be a potential device for non-invasive diagnosis of SARS-CoV-2 Omicron BA.2 variant, which is the variant of most concern because it is transmitted more rapidly than the original SARS-CoV-2 virus and the Delta variant.

Construction of a microcavity-based microfluidic chip with simultaneous SERS quantification of dual biomarkers for early diagnosis of Alzheimer's disease

Since there is no effective Alzheimer's disease (AD)-modifying therapy available currently, early analysis of AD core biomarkers has become one of great significance and common concern in clinical diagnosis. Herein, we designed an Au-plasmonic shell attached polystyrene (PS) microsphere in a microfluidic chip for simultaneous detection of Aβ1-42 and p-Tau181 protein. The corresponding Raman reporters were identified in femto gram level by ultrasensitive surface enhanced Raman spectroscopy (SERS). Both of Raman experimental data and finite-difference time-domain modeling demonstrates the synergetic coupling between PS microcavity with the optical confinement property and the localized surface plasmon resonance (LSPR) of AuNPs, so leading to highly amplified electromagnetic fields at the 'hot spot'. Moreover, the microfluidic system is designed with multiplex testing and control channels in which the AD-related dual proteins were detected quantitatively with a lower limit of 100 fg mL^-1. Thus, the proposed microcavity-based SERS strategy initiates a new way for accurately prediction of AD in human blood samples and provides the potential application for synchronous determination of multiple analytes in general disease assays.

Internet-of-medical-things integrated point-of-care biosensing devices for infectious diseases: Toward better preparedness for futuristic pandemics

Microbial pathogens have threatened the world due to their pathogenicity and ability to spread in communities. The conventional laboratory-based diagnostics of microbes such as bacteria and viruses need bulky expensive experimental instruments and skilled personnel which limits their usage in resource-limited settings. The biosensors-based point-of-care (POC) diagnostics have shown huge potential to detect microbial pathogens in a faster, cost-effective, and user-friendly manner. The use of various transducers such as electrochemical and optical along with microfluidic integrated biosensors further enhances the sensitivity and selectivity of detection. Additionally, microfluidic-based biosensors offer the advantages of multiplexed detection of analyte and the ability to deal with nanoliters volume of fluid in an integrated portable platform. In the present review, we discussed the design and fabrication of POCT devices for the detection of microbial pathogens which include bacteria, viruses, fungi, and parasites. The electrochemical techniques and current advances in this field in terms of integrated electrochemical platforms that include mainly microfluidic- based approaches and smartphone and Internet-of-things (IoT) and Internet-of-Medical-Things (IoMT) integrated systems have been highlighted. Further, the availability of commercial biosensors for the detection of microbial pathogens will be briefed. In the end, the challenges while fabrication of POC biosensors and expected future advances in the field of biosensing have been discussed. The integrated biosensor-based platforms with the IoT/IoMT usually collect the data to track the community spread of infectious diseases which would be beneficial in terms of better preparedness for current and futuristic pandemics and is expected to prevent social and economic losses.

Recent Advances in Molecular and Immunological Diagnostic Platform for Virus Detection: A Review

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused an ongoing coronavirus disease (COVID-19) outbreak and a rising demand for the development of accurate, timely, and cost-effective diagnostic tests for SARS-CoV-2 as well as other viral infections in general. Currently, traditional virus screening methods such as plate culturing and real-time PCR are considered the gold standard with accurate and sensitive results. However, these methods still require sophisticated equipment, trained personnel, and a long analysis time. Alternatively, with the integration of microfluidic and biosensor technologies, microfluidic-based biosensors offer the ability to perform sample preparation and simultaneous detection of many analyses in one platform. High sensitivity, accuracy, portability, low cost, high throughput, and real-time detection can be achieved using a single platform. This review presents recent advances in microfluidic-based biosensors from many works to demonstrate the advantages of merging the two technologies for sensing viruses. Different platforms for virus detection are classified into two main sections: immunoassays and molecular assays. Moreover, available commercial sensing tests are analyzed.

Hand-powered centrifugal micropipette-tip with distance-based quantification for on-site testing of SARS-CoV-2 virus

This paper proposed a hand-powered centrifugal micropipette-tip strategy, termed HCM, for all-in-one immunoassay combined with a distance-based readout for portable quantitative detection of SARS-CoV-2. The target SARS-CoV-2 virus antigen triggers the binding of multiple monoclonal antibody-coated red latex nanobeads, forming larger complexes. Following incubation and centrifugation, the formed aggregated complexes settle at the bottom of the tip, while free red nanobeads remain suspended in the solution. The HCM enables sensitive (1 ng/mL) and reliable quantification of SARS-CoV-2 within 25 min. With the advantages of free washing, free fabrication, free instrument, and without the optical device, the proposed low-cost and easy-to-use HCM immunoassay shows great potential for quantitative POC diagnostics for SARS-CoV-2.

Recent development of microfluidics-based platforms for respiratory virus detection

With the global outbreak of SARS-CoV-2, the inadequacies of current detection technology for respiratory viruses have been recognized. Rapid, portable, accurate, and sensitive assays are needed to expedite diagnosis and early intervention. Conventional methods for detection of respiratory viruses include cell culture-based assays, serological tests, nucleic acid detection (e.g., RT-PCR), and direct immunoassays. However, these traditional methods are often time-consuming, labor-intensive, and require laboratory facilities, which cannot meet the testing needs, especially during pandemics of respiratory diseases, such as COVID-19. Microfluidics-based techniques can overcome these demerits and provide simple, rapid, accurate, and cost-effective analysis of intact virus, viral antigen/antibody, and viral nucleic acids. This review aims to summarize the recent development of microfluidics-based techniques for detection of respiratory viruses. Recent advances in different types of microfluidic devices for respiratory virus diagnostics are highlighted, including paper-based microfluidics, continuous-flow microfluidics, and droplet-based microfluidics. Finally, the future development of microfluidic technologies for respiratory virus diagnostics is discussed.

Development of a New Lab-on-Paper Microfluidics Platform Using Bi-Material Cantilever Actuators for ELISA on Paper

In this paper, we present a novel and cost-effective lab-on-paper microfluidics platform for performing ELISA autonomously, with no user intervention beyond adding the sample. The platform utilizes two Bi-Material Cantilever Valves placed in a specially designed housing. The integration of these valves in a specific channel network forms a complete fluidic logic circuit for performing ELISA on paper. The housing also incorporates an innovative reagent storage and release mechanism that minimizes variability in the volume of reagents released into the reagent pads. The platform design was optimized to minimize variance in the time of fluid wicking from the reagent pad, using a randomized design of experiment. The platform adheres to the World Health Organization's ASSURED principles. The optimized design was used to conduct an ELISA for detecting rabbit immunoglobulin G (IgG) in a buffer, with a limit of detection of 2.27 ng/mL and a limit of quantification of 8.33 ng/mL. This represents a 58% improvement over previous ELISA methods for detecting rabbit IgG in buffer using portable microfluidic technology.

Electric yo-yo centrifugation combining with paper-based microfluidic immunoassay chip for inflammatory biomarkers detection in whole blood

At present, most countries or regions use commercial centrifuges for centrifugation, but this is out of reaching for limited-resource areas. To overcome this problem, a portable electric yo-yo as centrifuge was firstly proposed to obtain serum, and this device can be combined with paper-based analytical devices for enzyme-linked immunosorbent assay (ELISA) analysis from human whole blood. In this study, inflammatory biomarkers C-reactive protein (CRP) and serum amyloid A (SAA) were used as target biomarker to verify the performance of the proposed method. The results shows good performance and their detection limits were determined to be 580 pg/mL for CRP and 800 pg/mL for SAA, respectively. We believe this method provides a new platform of low cost and fast detection for inflammatory biomarkers in the limited-resource settings.

Fabrication of paper-based analytical devices by a laminating method with thermal ink ribbons, sticky notes, and office appliances

A stencil printing method utilizing sticky notes, a thermal transfer ink ribbon, and office appliances for paper-based analytical device (PAD) fabrication was proposed. A sticky note was attached to a filter paper, and a mask pattern was cut using a cutting machine. A commercially available thermal ink ribbon was then placed over the mask and laminated. We have characterized the fabricated devices. This approach could be used for the fast and mass prototyping of PADs using simple office appliances with no need for a wax printer.

Microfluidics for COVID-19: From Current Work to Future Perspective

Spread of coronavirus disease 2019 (COVID-19) has significantly impacted the public health and economic sectors. It is urgently necessary to develop rapid, convenient, and cost-effective point-of-care testing (POCT) technologies for the early diagnosis and control of the plague's transmission. Developing POCT methods and related devices is critical for achieving point-of-care diagnosis. With the advantages of miniaturization, high throughput, small sample requirements, and low actual consumption, microfluidics is an essential technology for the development of POCT devices. In this review, according to the different driving forces of the fluid, we introduce the common POCT devices based on microfluidic technology on the market, including paper-based microfluidic, centrifugal microfluidic, optical fluid, and digital microfluidic platforms. Furthermore, various microfluidic-based assays for diagnosing COVID-19 are summarized, including immunoassays, such as ELISA, and molecular assays, such as PCR. Finally, the challenges of and future perspectives on microfluidic device design and development are presented. The ultimate goals of this paper are to provide new insights and directions for the development of microfluidic diagnostics while expecting to contribute to the control of COVID-19.

Paper based microfluidic devices: a review of fabrication techniques and applications

A wide range of applications are possible with paper-based analytical devices, which are low priced, easy to fabricate and operate, and require no specialized equipment. Paper-based microfluidics offers the design of miniaturized POC devices to be applied in the health, environment, food, and energy sector employing the ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment free and Deliverable to end users) principle of WHO. Therefore, this field is growing very rapidly and ample research is being done. This review focuses on fabrication and detection techniques reported to date. Additionally, this review emphasises on the application of this technology in the area of medical diagnosis, energy generation, environmental monitoring, and food quality control. This review also presents the theoretical analysis of fluid flow in porous media for the efficient handling and control of fluids. The limitations of PAD have also been discussed with an emphasis to concern on the transformation of such devices from laboratory to the consumer.

Porous Cellulose Substrate Study to Improve the Performance of Diffusion-Based Ionic Strength Sensors

Microfluidic paper-based analytical devices (µPADs) are leading the field of low-cost, quantitative in-situ assays. However, understanding the flow behavior in cellulose-based membranes to achieve an accurate and rapid response has remained a challenge. Previous studies focused on commercial filter papers, and one of their problems was the time required to perform the test. This work studies the effect of different cellulose substrates on diffusion-based sensor performance. A diffusion-based sensor was laser cut on different cellulose fibers (Whatman and lab-made Sisal papers) with different structure characteristics, such as basis weight, density, pore size, fiber diameter, and length. Better sensitivity and faster response are found in papers with bigger pore sizes and lower basis weights. The designed sensor has been successfully used to quantify the ionic concentration of commercial wines with a 13.6 mM limit of detection in 30 s. The developed µPAD can be used in quantitative assays for agri-food applications without the need for any external equipment or trained personnel.

Emerging technologies for combating pandemics

INTRODUCTION

Covid-19, alongside previous pandemics, has highlighted the need for the continued development of technologies that are at our disposal. Emerging technologies are those that show true promise in achieving such a goal and have begun to form sturdy independent research areas. Technological advances in healthcare must continually develop to ensure that the world is prepared for any future diseases that may ensue. As such, a strategic review into 39 manuscripts since 2019 has been conducted to determine the prominence of emerging technologies since the beginning of the Covid-19 pandemic.

AREAS COVERED

Relating to their use in a pandemic state, additive manufacturing (AM), biofabrication, microfluidics, biomedical microelectromechanical systems (BioMEMS), and artificial intelligence (AI) are described. Applications over the past 2-3 years, as well as future developments, are considered throughout.

EXPERT OPINION

All the technologies mentioned in this review are sure to develop further, having shown their importance and value during the covid-19 pandemic. As research continues within the area, their efficacy will increase to the point where it likely will become gold standard for pandemic control. Combining certain technologies mentioned has also proved to have had great success in improving the final results obtained.

Forecasting the Post-Pandemic Effects of the SARS-CoV-2 Virus Using the Bullwhip Phenomenon Alongside Use of Nanosensors for Disease Containment and Cure

The COVID-19 pandemic has the tendency to affect various organizational paradigm alterations, which civilization hasyet to fully comprehend. Personal to professional, individual to corporate, and across most industries, the spectrum of transformations is vast. Economically, the globe has never been more intertwined, and it has never been subjected to such widespread disruption. While many people have felt and acknowledged the pandemic's short-term repercussions, the resultant paradigm alterations will certainly have long-term consequences with an unknown range and severity. This review paper aims at acknowledging various approaches for the prevention, detection, and diagnosis of the SARS-CoV-2 virus using nanomaterials as a base material. A nanostructure is a material classification based on dimensionality, in proportion to the characteristic diameter and surface area. Nanoparticles, quantum dots, nanowires (NW), carbon nanotubes (CNT), thin films, and nanocomposites are some examples of various dimensions, each acting as a single unit, in terms of transport capacities. Top-down and bottom-up techniques are used to fabricate nanomaterials. The large surface-to-volume ratio of nanomaterials allows one to create extremely sensitive charge or field sensors (electrical sensors, chemical sensors, explosives detection, optical sensors, and gas sensing applications). Nanowires have potential applications in information and communication technologies, low-energy lightning, and medical sensors. Carbon nanotubes have the best environmental stability, electrical characteristics, and surface-to-volume ratio of any nanomaterial, making them ideal for bio-sensing applications. Traditional commercially available techniques have focused on clinical manifestations, as well as molecular and serological detection equipment that can identify the SARS-CoV-2 virus. Scientists are expressing a lot of interest in developing a portable and easy-to-use COVID-19 detection tool. Several unique methodologies and approaches are being investigated as feasible advanced systems capable of meeting the demands. This review article attempts to emphasize the pandemic's aftereffects, utilising the notion of the bullwhip phenomenon's short-term and long-term effects, and it specifies the use of nanomaterials and nanosensors for detection, prevention, diagnosis, and therapy in connection to the SARS-CoV-2.

Research Progress and Future Trends of Microfluidic Paper-Based Analytical Devices in In-Vitro Diagnosis

In vitro diagnosis (IVD) has become a hot topic in laboratory research and achievement transformation. However, due to the high cost, and time-consuming and complex operation of traditional technologies, some new technologies are being introduced into IVD, to solve the existing problems. As a result, IVD has begun to develop toward point-of-care testing (POCT), a subdivision field of IVD. The pandemic has made governments and health institutions realize the urgency of accelerating the development of POCT. Microfluidic paper-based analytical devices (μPADs), a low-cost, high-efficiency, and easy-to-operate detection platform, have played a significant role in advancing the development of IVD. μPADs are composed of paper as the core material, certain unique substances as reagents for processing the paper, and sensing devices, as auxiliary equipment. The published reviews on the same topic lack a comprehensive and systematic introduction to μPAD classification and research progress in IVD segmentation. In this paper, we first briefly introduce the origin of μPADs and their role in promoting IVD, in the introduction section. Then, processing and detection methods for μPADs are summarized, and the innovative achievements of μPADs in IVD are reviewed. Finally, we discuss and prospect the upgrade and improvement directions of μPADs, in terms of portability, sensitivity, and automation, to help researchers clarify the progress and overcome the difficulties in subsequent μPAD research.

Virus Detection: From State-of-the-Art Laboratories to Smartphone-Based Point-of-Care Testing

Infectious virus outbreaks pose a significant challenge to public healthcare systems. Early and accurate virus diagnosis is critical to prevent the spread of the virus, especially when no specific vaccine or effective medicine is available. In clinics, the most commonly used viral detection methods are molecular techniques that involve the measurement of nucleic acids or proteins biomarkers. However, most clinic-based methods require complex infrastructure and expensive equipment, which are not suitable for low-resource settings. Over the past years, smartphone-based point-of-care testing (POCT) has rapidly emerged as a potential alternative to laboratory-based clinical diagnosis. This review summarizes the latest development of virus detection. First, laboratory-based and POCT-based viral diagnostic techniques are compared, both of which rely on immunosensing and nucleic acid detection. Then, various smartphone-based POCT diagnostic techniques, including optical biosensors, electrochemical biosensors, and other types of biosensors are discussed. Moreover, this review covers the development of smartphone-based POCT diagnostics for various viruses including COVID-19, Ebola, influenza, Zika, HIV, et al. Finally, the prospects and challenges of smartphone-based POCT diagnostics are discussed. It is believed that this review will aid researchers better understand the current challenges and prospects for achieving the ultimate goal of containing disease-causing viruses worldwide.

Microfluidics Technology in SARS-CoV-2 Diagnosis and Beyond: A Systematic Review

With the progression of the COVID-19 pandemic, new technologies are being implemented for more rapid, scalable, and sensitive diagnostics. The implementation of microfluidic techniques and their amalgamation with different detection techniques has led to innovative diagnostics kits to detect SARS-CoV-2 antibodies, antigens, and nucleic acids. In this review, we explore the different microfluidic-based diagnostics kits and how their amalgamation with the various detection techniques has spearheaded their availability throughout the world. Three other online databases, PubMed, ScienceDirect, and Google Scholar, were referred for articles. One thousand one hundred sixty-four articles were determined with the search algorithm of microfluidics followed by diagnostics and SARS-CoV-2. We found that most of the materials used to produce microfluidics devices were the polymer materials such as PDMS, PMMA, and others. Centrifugal force is the most commonly used fluid manipulation technique, followed by electrochemical pumping, capillary action, and isotachophoresis. The implementation of the detection technique varied. In the case of antibody detection, spectrometer-based detection was most common, followed by fluorescence-based as well as colorimetry-based. In contrast, antigen detection implemented electrochemical-based detection followed by fluorescence-based detection, and spectrometer-based detection were most common. Finally, nucleic acid detection exclusively implements fluorescence-based detection with a few colorimetry-based detections. It has been further observed that the sensitivity and specificity of most devices varied with implementing the detection-based technique alongside the fluid manipulation technique. Most microfluidics devices are simple and incorporate the detection-based system within the device. This simplifies the deployment of such devices in a wide range of environments. They can play a significant role in increasing the rate of infection detection and facilitating better health services.

A rotary multi-positioned cloth/paper hybrid microfluidic device for simultaneous fluorescence sensing of mercury and lead ions by using ion imprinted technologies

A novel rotary cloth/paper hybrid microfluidic analytical device (μCPAD) was proposed via the synergy of the fluorescence sensing cloth-based component and rotary paper-based microfluidic analytical device (μPAD) for simultaneous detection of mercury (Hg²⁺) and lead (Pb²⁺) ions. Fluorescence sensing cloth-based component was prepared by grafting quantum dots onto cotton cloth and then modifying with ion imprinted polymers (IIP). Because the cloth has good ductility and durability, it can bear strong oscillation during the fabrication of grafting quantum dots and IIP, and brings a lot of convenience to the production process. At the same time, because rotary μCPAD was stacked by three-layer papers with designed hydrophilic channels and hydrophobic barriers, it could realize simultaneous detection of Hg²⁺ and Pb²⁺ ions by rotating top layer counterclockwise or clockwise. The fluorescence signals were obtained through quantum dots' electron transfer fluorescence quenching effect with the limits of detection were 0.18 and 0.07 μg/L, respectively. This method successfully realized the transference of specific and sensitive fluorescence sensing materials (quantum dots) onto the microfluidic device to improve the portability and expanded applications. Moreover, the novel microfluidic device may have great potential in point-of-care testing of heavy metal ions in environmental monitoring fields.

A ZnFe2O4-catalyzed segment imprinted polymer on a three-dimensional origami paper-based microfluidic chip for the detection of microcystin

Microcystin has been causing serious environmental pollution; however, the recognition of such compounds is still challenging because of low abundance and coexisting interfering species. In this contribution, we develop a novel microfluidic paper-based colorimetric sensor by exploiting molecular imprinting technology and Fenton reaction for on-site microcystin-RR determination in complex water samples using a smartphone.

An origami paper-based analytical device for rapid detection of testosterone in healthcare food

An integrated origami paper-based analytical device (oPAD) based on competitive enzyme-linked immunosorbent assay (ELISA) was developed for testosterone (TES) detection. In this design, a positive correlation between the signals and analytes was observed due to the connection of the reaction zone and signal readout zone by a "detachable bridge". The device displayed rapid (35 min), sensitive (LOD: 1 μg L^-1) and highly selective characteristics for TES detection. In addition, complex matrices in healthcare food such as oral solutions and tablets showed a negligible effect on the accuracy of this assay (recovery: 95.4-109.1% and RSD < 6%), demonstrating its potential for hazardous chemical testing in real samples.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.

A novel polymer-based nitrocellulose platform for implementing a multiplexed microfluidic paper-based enzyme-linked immunosorbent assay

Nitrocellulose (NC) membranes, as porous paper-like substrates with high protein-binding capabilities, are very popular in the field of point-of-care immunoassays. However, generating robust hydrophobic structures in NC membranes to fabricate microfluidic paper-based analytical devices (μPADs) remains a great challenge. At present, the main method relies on an expensive wax printer. In addition, NC membranes very easy to adhere during the printing process due to electrostatic adsorption. Herein, we developed a facile, fast and low-cost strategy to fabricate μPADs in NC membranes by screen-printing polyurethane acrylate (PUA) as a barrier material for defining flow channels and reaction zones. Moreover, hydrophobic barriers based on UV-curable PUA can resist various surfactant solutions and organic solvents that are generally used in immunoassays and biochemical reactions. To validate the feasibility of this PUA-based NC membrane for immunoassays in point-of-care testing (POCT), we further designed and assembled a rotational paper-based analytical device for implementing a multiplexed enzyme-linked immunosorbent assay (ELISA) in a simple manner. Using the proposed device under the optimal conditions, alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA) could be identified, with limits of detection of 136 pg/mL and 174 pg/mL, respectively, which are below the threshold values of these two cancer biomarkers for clinical diagnosis. We believe that this reliable device provides a promising platform for the diagnosis of disease based on ELISA or other related bioassays in limited settings or remote regions.

An ion imprinting technology-assisted rotational microfluidic hybrid chip for the fluorescence detection of hexavalent chromium ions

An ion imprinted fluorescence sensing rotational microfluidic paper- and cloth-based hybrid chip was developed for hexavalent chromium detection.

Current Advances in Paper-Based Biosensor Technologies for Rapid COVID-19 Diagnosis

The global coronavirus disease 2019 (COVID-19) pandemic has had significant economic and social impacts on billions of people worldwide since severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in Wuhan, China, in November 2019. Although polymerase chain reaction (PCR)-based technology serves as a robust test to detect SARS-CoV-2 in patients with COVID-19, there is a high demand for cost-effective, rapid, comfortable, and accurate point-of-care diagnostic tests in medical facilities. This review introduces the SARS-CoV-2 viral structure and diagnostic biomarkers derived from viral components. A comprehensive introduction of a paper-based diagnostic platform, including detection mechanisms for various target biomarkers and a COVID-19 commercial kit is presented. Intrinsic limitations related to the poor performance of currently developed paper-based devices and unresolved issues are discussed. Furthermore, we provide insight into novel paper-based diagnostic platforms integrated with advanced technologies such as nanotechnology, aptamers, surface-enhanced Raman spectroscopy (SERS), and clustered regularly interspaced short palindromic repeats (CRISPR)-Cas. Finally, we discuss the prospects for the development of highly sensitive, accurate, cost-effective, and easy-to-use point-of-care COVID-19 diagnostic methods.

Paper-Based Biosensors for COVID-19: A Review of Innovative Tools for Controlling the Pandemic

The appearance and quick spread of the new severe acute respiratory syndrome coronavirus disease, COVID-19, brought major societal challenges. Importantly, suitable medical diagnosis procedures and smooth clinical management of the disease are an emergent need, which must be anchored on novel diagnostic methods and devices. Novel molecular diagnostic tools relying on nucleic acid amplification testing have emerged globally and are the current gold standard in COVID-19 diagnosis. However, the need for widespread testing methodologies for fast, effective testing in multiple epidemiological scenarios remains a crucial step in the fight against the COVID-19 pandemic. Biosensors have previously shown the potential for cost-effective and accessible diagnostics, finding applications in settings where conventional, laboratorial techniques may not be readily employed. Paper- and cellulose-based biosensors can be particularly relevant in pandemic times, for the renewability, possibility of mass production with sustainable methodologies, and safe environmental disposal. In this review, paper-based devices and platforms targeting SARS-CoV-2 are showcased and discussed, as a means to achieve quick and low-cost PoC diagnosis, including detection methodologies for viral genomic material, viral antigen detection, and serological antibody testing. Devices targeting inflammatory markers relevant for COVID-19 are also discussed, as fast, reliable bedside diagnostic tools for patient treatment and follow-up.