A "sample-in-multiplex-digital-answer-out" chip for fast detection of pathogens

Overview and Future Perspectives of Microfluidic Digital Recombinase Polymerase Amplification (dRPA)

Digital recombinase polymerase amplification (dRPA) aims to quantify the initial amount of nucleic acid by dividing nucleic acid and all reagents required for the RPA reaction evenly into numerous individual reaction units, such as chambers or droplets. dRPA turns out to be a prominent technique for quantifying the absolute quantity of target nucleic acid because of its advantages including low equipment requirements, short time consumption, as well as high sensitivity and specificity. dRPA combined with microfluidics are recognized as simple, various, and high-throughput nucleic acid quantization systems. This paper classifies the microfluidic dRPA systems over the last decade. We analyze and summarize the vital technologies of various microfluidic dRPA systems (e.g., chip preparation process, segmentation principle, microfluidic control, and statistical analysis methods), and major efforts to address limitations (e.g., prevention of evaporation and contamination, accurate initiation, and reduction of manual operation). In addition, this paper summarizes key factors and potential constraints to the success of the microfluidic dRPA to help more researchers, and possible strategies to overcome the mentioned challenges. Lastly, actual suggestions and strategies are proposed for the subsequent development of microfluidic dRPA.

Multiplex optical bioassays for food safety analysis: Toward on-site detection

Food safety analysis plays a significant role in controlling food contamination and supervision. In recent years, multiplex optical bioassays (MOBAs) have been widely applied to analyze multiple hazards due to their efficiency and low cost. However, due to the challenges such as multiplexing capacity, poor sensitivity, and bulky instrumentation, the further application of traditional MOBAs in food screening has been limited. In this review, effective strategies regarding food safety MOBAs are summarized, such as spatial-resolution modes performed in multi-T lines/dots strips or arrays of strip/microplate/microfluidic chip/SPR chip and signal-resolution modes employing distinguishable colorimetric/luminescence/fluorescence/surface plasma resonance/surface-enhanced Raman spectrum as signal tags. Following this, new trends on how to design engineered sensor architecture and exploit distinguishable signal reporters, how to improve both multiplexing capacity and sensitivity, and how to integrate these formats into smartphones so as to be mobile are summarized systematically. Typically, in the case of enhancing multiplexing capacity and detection throughput, microfluidic array chips with multichannel architecture would be a favorable approach to overcome the spatial and physical limitations of immunochromatographic assay (ICA) test strips. Moreover, noble metal nanoparticles and single-excitation, multiple-emission luminescence nanomaterials hold great potential in developing ultrasensitive MOBAs. Finally, the exploitation of innovative multiplexing strategy hybridized with powerful and widely available smartphones opens new perspectives to MOBAs. In future, the MOBAs should be more sensitive, have higher multiplexing capacity, and easier instrumentation.

Biosensors and Point-of-Care Devices for Bacterial Detection: Rapid Diagnostics Informing Antibiotic Therapy

With an exponential rise in antimicrobial resistance and stagnant antibiotic development pipeline, there is, more than ever, a crucial need to optimize current infection therapy approaches. One of the most important stages in this process requires rapid and effective identification of pathogenic bacteria responsible for diseases. Current gold standard techniques of bacterial detection include culture methods, polymerase chain reactions, and immunoassays. However, their use is fraught with downsides with high turnaround time and low accuracy being the most prominent. This imposes great limitations on their eventual application as point-of-care devices. Over time, innovative detection techniques have been proposed and developed to curb these drawbacks. In this review, a systematic summary of a range of biosensing platforms is provided with a strong focus on technologies conferring high detection sensitivity and specificity. A thorough analysis is performed and the benefits and drawbacks of each type of biosensor are highlighted, the factors influencing their potential as point-of-care devices are discussed, and the authors' insights for their translation from proof-of-concept systems into commercial medical devices are provided.

Recombinase polymerase amplification integrated with microfluidics for nucleic acid testing at point of care

Nucleic acid testing (NAT) implemented on a portable, miniaturized, and integrated device with rapid and sensitive results readout is highly demanded for pathogen detection or genetic screening at resource-limited settings, especially after the outbreak of coronavirus disease 2019 (COVID-19). The integration of recombinase polymerase amplification (RPA) with emerging microfluidics, classified by paper-based microfluidics and chip-based microfluidics, shows great potential to perform laboratory independent NAT assays at point of care with minimal labor, time and energy consumption. This review summarizes the state-of-the-art of RPA integrated with paper-based microfluidics and chip-based microfluidics, and discusses their pros and cons. Finally, existing challenges and possible ways for optimization of microfluidics-based RPA are proposed.

A genosensor for detecting single-point mutations in dendron chips after blocked recombinase polymerase amplification

Dendron–probe conjugates were effectively immobilized on chip surfaces, improving assay sensitivity and simplifying coupling reactions. Combined with an isothermal amplification, the array method accurately detects single-base changes.

A sample-to-answer DNA detection microfluidic system integrating sample pretreatment and smartphone-readable gradient plasmonic photothermal continuous-flow PCR

We report a microfluidic system integrating sample pretreatment and smartphone-readable gradient plasmonic photothermal continuous-flow PCR, paving the way for low-cost and rapid implementation of PCR diagnostics.

Point-of-Care Testing-The Key in the Battle against SARS-CoV-2 Pandemic

The deleterious effects of the coronavirus disease 2019 (COVID-19) pandemic urged the development of diagnostic tools to manage the spread of disease. Currently, the "gold standard" involves the use of quantitative real-time polymerase chain reaction (qRT-PCR) for SARS-CoV-2 detection. Even though it is sensitive, specific and applicable for large batches of samples, qRT-PCR is labour-intensive, time-consuming, requires trained personnel and is not available in remote settings. This review summarizes and compares the available strategies for COVID-19: serological testing, Point-of-Care Testing, nanotechnology-based approaches and biosensors. Last but not least, we address the advantages and limitations of these methods as well as perspectives in COVID-19 diagnostics. The effort is constantly focused on understanding the quickly changing landscape of available diagnostic testing of COVID-19 at the clinical levels and introducing reliable and rapid screening point of care testing. The last approach is key to aid the clinical decision-making process for infection control, enhancing an appropriate treatment strategy and prompt isolation of asymptomatic/mild cases. As a viable alternative, Point-of-Care Testing (POCT) is typically low-cost and user-friendly, hence harbouring tremendous potential for rapid COVID-19 diagnosis.

Application of Lab-on-Chip for Detection of Microbial Nucleic Acid in Food and Environment

Various diseases caused by food-borne or environmental pathogenic microorganisms have been a persistent threat to public health and global economies. It is necessary to regularly detect microorganisms in food and environment to prevent infection of pathogenic microorganisms. However, most traditional detection methods are expensive, time-consuming, and unfeasible in practice in the absence of sophisticated instruments and trained operators. Point-of-care testing (POCT) can be used to detect microorganisms rapidly on site and greatly improve the efficiency of microbial detection. Lab-on-chip (LOC) is an emerging POCT technology with great potential by integrating most of the experimental steps carried out in the laboratory into a single monolithic device. This review will primarily focus on principles and techniques of LOC for detection of microbial nucleic acid in food and environment, including sample preparation, nucleic acid amplification and sample detection.

Biochemical composition, transmission and diagnosis of SARS-CoV-2

Coronavirus disease 2019 (COVID-19) is a life-threatening respiratory infection caused by severe acute respiratory syndrome virus (SARS-CoV-2), a novel human coronavirus. COVID-19 was declared a pandemic by World Health Organization in March 2020 for its continuous and rapid spread worldwide. Rapidly emerging COVID-19 epicenters and mutants of concerns have created mammoth chaos in healthcare sectors across the globe. With over 185 million infections and approximately 4 million deaths globally, COVID-19 continues its unchecked spread despite all mitigation measures. Until effective and affordable antiretroviral drugs are made available and the population at large is vaccinated, timely diagnosis of the infection and adoption of COVID-appropriate behavior remains major tool available to curtail the still escalating COVID-19 pandemic. This review provides an updated overview of various techniques of COVID-19 testing in human samples and also discusses, in brief, the biochemical composition and mode of transmission of the SARS-CoV-2. Technological advancement in various molecular, serological and immunological techniques including mainly the reverse-transcription polymerase chain reaction (RT-PCR), CRISPR, lateral flow assays (LFAs), and immunosensors are reviewed.

Label-free E. coli detection based on enzyme assay and a microfluidic slipchip

An enzyme assay based method in a microfluidic slipchip was proposed for the rapid and label-free detection of E. coli. The specific target analyte of E. coli was β-d-glucuronidase (GUS) which could catalyze the substrate 6-chloro-4-methyl-umbelliferyl-β-d-glucuronide (6-CMUG) to release the fluorescent molecule 6-chloro-4-methyl-umbelliferyl (6-CMU). E. coli culture, lysis and enzymatic reaction steps could be conducted in a microfluidic slipchip without any pumps and valves, which was tailored for fluorescence detection using a commercial plate reader, to achieve a rapid E. coli test. A mixture of the culture broth, enzyme inducer and E. coli was injected into the chambers on the top layer. A mixture of the substrate and lysis solution was injected into the chambers on the bottom layer. Then, the slipchip was slid to make each chamber independent. E. coli was cultured in the chamber in the LB broth for 2.5 h. After that, the slipchip was slid again to introduce the lysis solution into the culture solution for GUS release and enzyme reaction, and then incubated in the plate reader at 42 °C for another 2.5 h. During incubation, the fluorescence intensity of each chamber was recorded. This proposed label-free method can directly detect E. coli with a low concentration of 8 CFU per chamber within 5 h, thus showing great potential in on-site E. coli detection.

Recent innovations in cost-effective polymer and paper hybrid microfluidic devices

Hybrid microfluidic systems that are composed of multiple different types of substrates have been recognized as a versatile and superior platform, which can draw benefits from different substrates while avoiding their limitations. This review article introduces the recent innovations of different types of low-cost hybrid microfluidic devices, particularly focusing on cost-effective polymer- and paper-based hybrid microfluidic devices. In this article, the fabrication of these hybrid microfluidic devices is briefly described and summarized. We then highlight various hybrid microfluidic systems, including polydimethylsiloxane (PDMS)-based, thermoplastic-based, paper/polymer hybrid systems, as well as other emerging hybrid systems (such as thread-based). The special benefits of using these hybrid systems have been summarized accordingly. A broad range of biological and biomedical applications using these hybrid microfluidic devices are discussed in detail, including nucleic acid analysis, protein analysis, cellular analysis, 3D cell culture, organ-on-a-chip, and tissue engineering. The perspective trends of hybrid microfluidic systems involving the improvement of fabrication techniques and broader applications are also discussed at the end of the review.

A New Direction in Microfluidics: Printed Porous Materials

In this work, the feasibility of a novel direction for microfluidics is studied by demonstrating a set of new methods to fabricate microfluidic systems. Similarly to microfluidic paper-based analytical devices, porous materials are being used. However, alternative porous materials and different printing methods are used here to give the material the necessary pattern to act as a microfluidic system. In this work, microfluidic systems were produced by the following three separate methods: (1) by curing a porous monolithic polymer sheet into a necessary pattern with photolithography, (2) by screen printing silica gel particles with gypsum, and (3) by dispensing silica gel particles with polyvinyl acetate binder using a modified 3D printer. Different parameters of the printed chips were determined (strength of the printed material, printing accuracy, printed material height, wetting characteristics, repeatability) to evaluate whether the printed chips were suitable for use in microfluidics. All three approaches were found to be suitable, and therefore the novel approach to microfluidics was successfully demonstrated.

Recent Advances in Microfluidic Devices for Contamination Detection and Quality Inspection of Milk

Milk is a necessity for human life. However, it is susceptible to contamination and adulteration. Microfluidic analysis devices have attracted significant attention for the high-throughput quality inspection and contaminant analysis of milk samples in recent years. This review describes the major proposals presented in the literature for the pretreatment, contaminant detection, and quality inspection of milk samples using microfluidic lab-on-a-chip and lab-on-paper platforms in the past five years. The review focuses on the sample separation, sample extraction, and sample preconcentration/amplification steps of the pretreatment process and the determination of aflatoxins, antibiotics, drugs, melamine, and foodborne pathogens in the detection process. Recent proposals for the general quality inspection of milk samples, including the viscosity and presence of adulteration, are also discussed. The review concludes with a brief perspective on the challenges facing the future development of microfluidic devices for the analysis of milk samples in the coming years.

A microfluidic colorimetric biosensor for in-field detection of Salmonella in fresh-cut vegetables using thiolated polystyrene microspheres, hose-based microvalve and smartphone imaging APP

A microfluidic colorimetric biosensor was developed using thiolated polystyrene microspheres (SH-PSs) for aggregating of gold nanoparticles (AuNPs), a novel hose-based microvalve for controlling the flow direction, and a smartphone imaging APP for monitoring colorimetric signals. Aptamer-PS-cysteamine conjugates were used as detection probes and reacted with Salmonella in samples. Complementary DNA - magnetic nanoparticle (cDNA - MNP) conjugates were used as capture probes, reacted with the free aptamer-PS-cysteamine conjugates. AuNPs were aggregated on the surface of Salmonella-aptamer-PS-cysteamine conjugates, resulting in a visible color change in the detection chamber, which indicating different concentrations of Salmonella. The limit of detection was low to 6.0 × 10¹ cfu/mL. The microfluidic biosensor exhibited a good specificity. It was evaluated by analyzing salad samples spiked with Salmonella. The recoveries ranged from 91.68% to 113.76%, which indicated its potential application in real samples.

Microfluidic devices for multiplexed detection of foodborne pathogens

The global burden of foodborne diseases is substantial and foodborne pathogens are the major cause for human illnesses. In order to prevent the spread of foodborne pathogens, detection methods are constantly being updated towards rapid, portable, inexpensive, and multiplexed on-site detection. Due to the nature of the small size and low volume, microfluidics has been applied to rapid, time-saving, sensitive, and portable devices to meet the requirements of on-site detection. Simultaneous detection of multiple pathogens is another key parameter to ensure food safety. Multiplexed detection technology, including microfluidic chip design, offers a new opportunity to achieve this goal. In this review, we introduced several sample preparation and corresponding detection methods on microfluidic devices for multiplexed detection of foodborne pathogens. In the sample preparation section, methods of cell capture and enrichment, as well as nucleic acid sample preparation, were described in detail, and in the section of detection methods, amplification, immunoassay, surface plasmon resonance and impedance spectroscopy were exhaustively illustrated. The limitations and advantages of all available experimental options were also summarized and discussed in order to form a comprehensive understanding of cutting-edge technologies and provide a comparative assessment for future investigation and in-field application.

Multiplex Molecular Point-of-Care Test for Syndromic Infectious Diseases

Point-of-care (POC) molecular diagnostics for clinical microbiology and virology has primarily focused on the detection of a single pathogen. More recently, it has transitioned into a comprehensive syndromic approach that employs multiplex capabilities, including the simultaneous detection of two or more pathogens. Multiplex POC tests provide higher accuracy to for actionable decisionmaking in critical care, which leads to pathogen-specific treatment and standardized usages of antibiotics that help prevent unnecessary processes. In addition, these tests can be simple enough to operate at the primary care level and in remote settings where there is no laboratory infrastructure. This review focuses on state-of-the-art multiplexed molecular point-of-care tests (POCT) for infectious diseases and efforts to overcome their limitations, especially related to inadequate throughput for the identification of syndromic diseases. We also discuss promising and imperative clinical POC approaches, as well as the possible hurdles of their practical applications as front-line diagnostic tests.

Microfluidics for the rapid detection of Escherichia coli O157:H7 using antibody-coated microspheres

This study developed a novel method for the rapid detection of Escherichia coli (E. coli) O157:H7 on a microfluidic platform. First, the concentration of bacteria in a sample was determined with the adenosine triphosphate (ATP) method. Then, the specific detection of E. coli was achieved in a microfluidic chip by the immune-microsphere technique. The influences of the culture time, flow rate and capture time on the detection of the target bacteria were investigated systematically. Generally, with increasing capture time, more bacteria could be captured by the microspheres, which had a positive effect on bacterial detection. Furthermore, the sensitivity and specificity of the method were also tested. The results showed that this method could specifically detect E. coli with a sensitivity as high as 49.1 cfu/μL; the consumption of bacteria was 1 μL, and the reagent was at the microliter level. The testing time can be controlled within one and a half hours, and the cost of testing was approximately RMB 10. The method described in this article is simple and accurate and has great application value in bacterial detection for medical diagnostics.

Fully integrated microfluidic devices for qualitative, quantitative and digital nucleic acids testing at point of care

Benefiting from emerging miniaturized and equipment-free nucleic acid testing (NAT) technologies, fully integrated NAT devices at point of care (POC) with the capability of "sample-in-answer-out" are proceeding at a break-neck speed to eliminate complex operations and reduce the risk of contamination. Like the development of polymerase chain reaction (PCR) technology (the standard technique for NAT), the detection signal of fully integrated NAT devices has evolved from qualitative to quantitative and recently to digital readout, aiming at expanding their extensive applications through gradually improving detection sensitivity and accuracy. This review firstly introduces the existing commercial products, and then illustrates recent fully integrated microfluidic devices for NAT at POC from the aspect of detection signals (i.e., qualitative, quantitative and digital). Importantly, the key issues of existing commercial products and the main challenges between scientific research and product development are discussed. On this basis, we envision that the MARCHED (miniaturized, automatic, reagent-preloaded, commercializable, high-throughput, environment-independent and disposable) NAT devices are expected to be realized in the near future.

Biosensors for the Detection of Bacterial and Viral Clinical Pathogens

Biosensors are measurement devices that can sense several biomolecules, and are widely used for the detection of relevant clinical pathogens such as bacteria and viruses, showing outstanding results. Because of the latent existing risk of facing another pandemic like the one we are living through due to COVID-19, researchers are constantly looking forward to developing new technologies for diagnosis and treatment of infections caused by different bacteria and viruses. Regarding that, nanotechnology has improved biosensors' design and performance through the development of materials and nanoparticles that enhance their affinity, selectivity, and efficacy in detecting these pathogens, such as employing nanoparticles, graphene quantum dots, and electrospun nanofibers. Therefore, this work aims to present a comprehensive review that exposes how biosensors work in terms of bacterial and viral detection, and the nanotechnological features that are contributing to achieving a faster yet still efficient COVID-19 diagnosis at the point-of-care.

Microfluidics for the rapid detection of Staphylococcus aureus using antibody-coated microspheres

Staphylococcus aureus is a common foodborne pathogenic microorganism which can cause food poisoning and it is pathogenic to both humans and animals. Therefore, rapid detection of S. aureus infection is of great significance. In this study, a microfluidic platform was introduced to detect S. aureus by fluorescence labeling method and a self-made microfluidic chip, which has immune spheres were used to study the effect of capturing S. aureus. Through this experiment, we found that the platform can be used for microbial culture, and S. aureus antibody coated on the diameter of 50 ~ 90 μm microspheres for detection. On the premise of optimizing the sample flow rate and detection time, the bacterial detection was quantitatively monitored. Results showed that our platform can detect S. aureus at injection rate of 5 μL·min⁻¹ reacted for 4 min and the detection limit of bacteria is 1.5 × 10¹ CFU/μL. However, the detection time of traditional method is 24 hs to 72 hs, and the operation is complex and cumbersome. These findings indicated that the microfluidic chip in this study is portable, sensitive, and accurate, laying a good foundation for further research on the application of rapid bacterial detection platform.

Detection of COVID-19: A review of the current literature and future perspectives

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to the coronavirus disease 2019 (COVID-19) worldwide pandemic. This unprecedented situation has garnered worldwide attention. An effective strategy for controlling the COVID-19 pandemic is to develop highly accurate methods for the rapid identification and isolation of SARS-CoV-2 infected patients. Many companies and institutes are therefore striving to develop effective methods for the rapid detection of SARS-CoV-2 ribonucleic acid (RNA), antibodies, antigens, and the virus. In this review, we summarize the structure of the SARS-CoV-2 virus, its genome and gene expression characteristics, and the current progression of SARS-CoV-2 RNA, antibodies, antigens, and virus detection. Further, we discuss the reasons for the observed false-negative and false-positive RNA and antibody detection results in practical clinical applications. Finally, we provide a review of the biosensors which hold promising potential for point-of-care detection of COVID-19 patients. This review thereby provides general guidelines for both scientists in the biosensing research community and for those in the biosensor industry to develop a highly sensitive and accurate point-of-care COVID-19 detection system, which would be of enormous benefit for controlling the current COVID-19 pandemic.

Current progress on COVID-19 related to biosensing technologies: New opportunity for detection and monitoring of viruses

•

COVID-19 infection poses a serious risk to human life by causing acute lung damage.

•

Various techniques used to identify and quantify COVID-19 infection.

•

Major challenges for containing the spread of COVID-19 is the ability to identify asymptomatic cases.

•

Currently available diagnostic methods, biosensing technology developed during COVID-19 infection.

The technologies used for coronavirus testing consist of a pre-existing device developed to examine different pathologies, such as bacterial infections, or cancer biomarkers. However, for the 2019 pandemic, researchers knew that their technology could be modified to detect a low viral load at an early stage. Today, countries around the world are working to control the new coronavirus disease (n-SARS-CoV-2). From this perspective, laboratories, universities, and companies around the world have embarked on a race to develop and produce much-needed test kits. This review has been developed to provide an overview of current trends and strategies in n-SARS-CoV-2 diagnostics based on traditional and new emerging assessment technologies, to continuous innovation. It focuses on recent trends in biosensors to build a fast, reliable, more sensitive, accessible, user-friendly system and easily adaptable technology n-SARS-CoV-2 detection and monitoring. On the whole, we have addressed and identified research evidence supporting the use of biosensors on the premise that screening people for n-SARS-CoV-2 is the best way to contain its spread.

A self-powered bidirectional partition microfluidic chip with embedded microwells for highly sensitive detection of EGFR mutations in plasma of non-small cell lung cancer patients

Circulating tumor DNA (ctDNA) is a promising biomarker for tumor genotyping and therapy monitoring. Herein, we developed a digital PCR chip with embedded microwell and bidirectional partition network for highly sensitive ctDNA analysis. The embedded microwell contributes to increasing microreaction density (up to 7000 microwells/cm²) and reducing evaporation during amplification. The bidirectional partition network can achieve fast and random distribution of targets, ensuring the precise quantification of nucleic acid. We used plasmids, artificial samples and 32 clinical blood samples from non-small cell lung cancer patients to test the performance of this platform. The results demonstrated that our chip has not only comparable quantification performance to commercial counterpart but also the ability to detect EGFR mutations with as low as 0.01% mutation rate and 20 alter molecules in 27 ng genomic DNA. The identification of EGFR mutations in plasma using developed chip exhibited 85.71% sensitivity and 94.44% specificity for L858R mutation and 100% sensitivity and 86.96% specificity for T790 M mutation. Moreover, the monitoring of mutant allele in plasma was accomplished in this work. In conclusion, the developed chip has a potential in lung tumor genotyping and therapy monitoring for precision medicine, even other tumors.

A lab-on-chip device for the sample-in-result-out detection of viable Salmonella using loop-mediated isothermal amplification and real-time turbidity monitoring

Rapid screening of foodborne pathogens is key to prevent food poisoning. In this study, a lab-on-chip device was developed for rapid, automatic and sensitive detection of viable Salmonella typhimurium using loop-mediated isothermal amplification (LAMP) and smartphone real-time turbidity monitoring. First, magnetic nanoparticles (MNPs) coated with anti-Salmonella capture antibodies in propidium monoazide (PMA) were fully mixed with bacterial samples using two active magnetic stirring mixers at reverse rotating directions, and incubated in the serpentine channel with 470 nm blue light exposure, allowing specific formation of magnetic bacteria and sufficient PMA pretreatment of the DNA of dead bacteria. Then, the PMA-treated magnetic bacteria were separated in the separation chamber using the magnetic field and their genomic DNA templates were extracted using lysis buffer at 70 °C. Finally, the viable bacteria's DNA was amplified using LAMP in the detection chamber preloaded with the lyophilized LAMP reagents at 67.5 °C after blocking with paraffin oil to avoid aerosol cross contamination. Finally, the turbidity of the LAMP reaction system was monitored in a real-time manner for the quantitative detection of viable bacteria. The experimental results demonstrated that this device was able to automatically detect viable Salmonella as low as 14 CFU mL-1 in spiked chicken meat supernatants within 1.5 h. This device is very promising to provide a sample-in-result-out solution for the in-field detection of Salmonella and could be easily extended for other foodborne pathogens.

Clip-to-release on amplification (CRoA): a novel DNA amplification enhancer on and off microfluidics

Despite its high sensitivity, low cost, and high efficiency as a DNA amplification indicator with a yes/no answer, dsDNA-binding dye encounters incompatibility when used in microfluidic systems, resulting in problems such as false negative amplification results. Besides, its inhibition of amplification at high concentrations hinders its application both on-chip and off-chip. In this study, we propose a novel DNA amplification enhancer to counteract the drawbacks of dsDNA-binding dyes. It acts as a temporary reservoir for the free-floating dyes in solution and releases them on demand during the amplification process. Through this clip-to-release on amplification mechanism, the enhancer lowered the background fluorescence of sample droplets before amplification, enhanced the signal-to-background ratio of positive samples, and eliminated the false negative signal of on-chip PCR. Moreover, the enhancer increased the off-chip polymerase chain reaction (PCR) efficiency, boosted the fluorescence signal up to 10-fold, and made less nonspecific amplification product. All the factors affecting the enhancer's performance are investigated in detail, including its structure and concentration, and the types of dsDNA-binding dye used in the reaction. Finally, we demonstrated the broad application of the proposed amplification enhancer in various DNA amplification systems, for various genes, and on various amplification platforms. It would reignite the utilization of dsDNA dyes for wider applications in DNA analysis both on-chip and off-chip.

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

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

Development of Point-of-Care Biosensors for COVID-19

Coronavirus disease 2019 (COVID-19) outbreak has become a global pandemic. The deleterious effects of coronavirus have prompted the development of diagnostic tools to manage the spread of disease. While conventional technologies such as quantitative real time polymerase chain reaction (qRT-PCR) have been broadly used to detect COVID-19, they are time-consuming, labor-intensive and are unavailable in remote settings. Point-of-care (POC) biosensors, including chip-based and paper-based biosensors are typically low-cost and user-friendly, which offer tremendous potential for rapid medical diagnosis. This mini review article discusses the recent advances in POC biosensors for COVID-19. First, the development of POC biosensors which are made of polydimethylsiloxane (PDMS), papers, and other flexible materials such as textile, film, and carbon nanosheets are reviewed. The advantages of each biosensors along with the commercially available COVID-19 biosensors are highlighted. Lastly, the existing challenges and future perspectives of developing robust POC biosensors to rapidly identify and manage the spread of COVID-19 are briefly discussed.