A new point-of-care test for the diagnosis of infectious diseases based on multiplex lateral flow immunoassays

Paper-Based procalcitonin and Interleukin-6 test strip with Spectrum-Based optical reader for enterovirus severity differentiation in children

Infectious diseases significantly impact global health, necessitating prompt diagnosis to mitigate life-threatening sepsis risk. Identifying patients at risk of severe neurological complications from enterovirus infections is challenging due to nonspecific initial presentations. Point-of-care testing (POCT) has emerged as a transformative tool, with low-cost lateral-flow colorimetric assays showing promise in deployable POCT devices. We developed a PCT/IL-6 rapid diagnostic system integrating lateral flow assay (LFA) test strips and a portable optical spectrum reader, allowing simultaneous semi-quantitative measurement of serum PCT and IL-6 within 30 min at the point of care. The system demonstrated a strong correlation with traditional ELISA and effectively differentiated severe pediatric enterovirus cases using serum samples. IL-6 showed superior discriminatory ability over PCT in identifying patients with severe neurological complications. This novel diagnostic platform holds great potential for early sepsis recognition and infectious disease management, especially in resource-limited settings.

The significance of antigen-antibody-binding avidity in clinical diagnosis

Immunoglobulin G (IgG) and immunoglobulin M (IgM) testing are commonly used to determine infection status. Typically, the detection of IgM indicates an acute or recent infection, while the presence of IgG alone suggests a chronic or past infection. However, relying solely on IgG and IgM antibody positivity may not be sufficient to differentiate acute from chronic infections. This limitation arises from several factors. The prolonged presence of IgM can complicate diagnostic interpretations, and false positive IgM results often arise from antibody cross-reactivity with various antigens. Additionally, IgM may remain undetectable in prematurely collected samples or in individuals who are immunocompromised, further complicating accurate diagnosis. As a result, additional diagnostic tools are required to confirm infection status. Avidity is a measure of the strength of the binding between an antigen and antibody. Avidity-based assays have been developed for various infectious agents, including toxoplasma, cytomegalovirus (CMV), SARS-CoV-2, and avian influenza, and are promising tools in clinical diagnostics. By measuring the strength of antibody binding, they offer critical insights into the maturity of the immune response. These assays are instrumental in distinguishing between acute and chronic or past infections, monitoring disease progression, and guiding treatment decisions. The development of automated platforms has optimized the testing process by enhancing efficiency and minimizing the risk of manual errors. Additionally, the recent advent of real-time biosensor immunoassays, including the label-free immunoassays (LFIA), has further amplified the capabilities of these assays. These advances have expanded the clinical applications of avidity-based assays, making them useful tools for the diagnosis and management of various infectious diseases. This review is structured around several key aspects of IgG avidity in clinical diagnosis, including: (i) a detailed exposition of the IgG affinity maturation process; (ii) a thorough discussion of the IgG avidity assays, including the recently emerged biosensor-based approaches; and (iii) an examination of the applications of IgG avidity in clinical diagnosis. This review is intended to contribute toward the development of enhanced diagnostic tools through critical assessment of the present landscape of avidity-based testing, which allows us to identify the existing knowledge gaps and highlight areas for future investigation.

Development of a nucleic acid detection method based on the CRISPR-Cas13 for point-of-care testing of bovine viral diarrhea virus-1b

Bovine viral diarrhea (BVD) is a single-stranded, positive-sense ribonucleic acid (RNA) virus belonging to the genus Pestivirus of the Flaviviridae family. BVD frequently causes economic losses to farmers. Among bovine viral diarrhea virus (BVDV) strains, BVDV-1b is predominant and widespread in Hanwoo calves. Reverse-transcription polymerase chain reaction (RT-PCR) is an essential method for diagnosing BVDV-1b and has become the gold standard for diagnosis in the Republic of Korea. However, this diagnostic method is time-consuming and requires expensive equipment. Therefore, Clustered regularly interspaced short palindromic repeats-Cas (CRISPR-Cas) systems have been used for point-of-care (POC) testing of viruses. Developing a sensitive and specific method for POC testing of BVDV-1b would be advantageous for controlling the spread of infection. Thus, this study aimed to develop a novel nucleic acid detection method using the CRISPR-Cas13 system for POC testing of BVDV-1b. The sequence of the BVD virus was extracted from National Center for Biotechnology Information (NC_001461.1), and the 5' untranslated region, commonly used for detection, was selected. CRISPR RNA (crRNA) was designed using the Cas13 design program and optimized for the expression and purification of the LwCas13a protein. Madin Darby bovine kidney (MDBK) cells were infected with BVDV-1b, incubated, and the viral RNA was extracted. To enable POC viral detection, the compatibility of the CRISPR-Cas13 system was verified with a paper-based strip through collateral cleavage activity. Finally, a colorimetric assay was used to evaluate the detection of BVDV-1b by combining the previously obtained crRNA and Cas13a protein on a paper strip. In conclusion, the CRISPR-Cas13 system is highly sensitive, specific, and capable of nucleic acid detection, making it an optimal system for the early point-of-care testing of BVDV-1b.

Paper-based sensors: affordable, versatile, and emerging analyte detection platforms

Paper-based sensors, often referred to as paper-based analytical devices (PADs), stand as a transformative technology in the field of analytical chemistry. They offer an affordable, versatile, and accessible solution for diverse analyte detection. These sensors harness the unique properties of paper substrates to provide a cost-effective and adaptable platform for rapid analyte detection, spanning chemical species, biomolecules, and pathogens. This review highlights the key attributes that make paper-based sensors an attractive choice for analyte detection. PADs demonstrate their versatility by accommodating a wide range of analytes, from ions and gases to proteins, nucleic acids, and more, with customizable designs for specific applications. Their user-friendly operation and minimal infrastructure requirements suit point-of-care diagnostics, environmental monitoring, food safety, and more. This review also explores various fabrication methods such as inkjet printing, wax printing, screen printing, dip coating, and photolithography. Incorporating nanomaterials and biorecognition elements promises even more sophisticated and sensitive applications.

UbiNAAT: a multiplexed point-of-care nucleic acid diagnostic platform for rapid at-home pathogen detection

The COVID-19 pandemic increased demands for respiratory disease testing to facilitate treatment and limit transmission, demonstrating in the process that most existing test options were too complex and expensive to perform in point-of-care or home scenarios. Lab-based molecular techniques can detect viral RNA in respiratory illnesses but are expensive and require trained personnel, while affordable antigen-based home tests lack sensitivity for early detection in newly infected or asymptomatic individuals. The few home RNA detection tests deployed were prohibitively expensive. Here, we demonstrate a point-of-care, paper-based rapid analysis device that simultaneously detects multiple viral RNAs; it is demonstrated on two common respiratory viruses (COVID-19 and influenza A) spiked onto a commercial nasal swab. The automated device requires no sample preparation by the user after insertion of the swab, minimizing user operation steps. We incorporated lyophilized amplification reagents immobilized in a porous matrix, a novel thermally actuated valve for multiplexed fluidic control, a printed circuit board that performs on-device lysis and amplification within a cell-phone-sized disposable device. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) products are visualized via fluorescent dyes using a modified cell phone, resulting in detection of as few as 104 viral copies per swab across both pathogens within 30 minutes. This integrated platform could be commercialized in a form that would be inexpensive, portable, and sensitive; it can readily be multiplexed to detect as many as 8 different RNA or DNA sequences, and adapted to any desired RNA or DNA detection assays.

Innovation and Patenting Activities During COVID-19 and Advancement of Biochemical and Molecular Diagnosis in the Post- COVID-19 Era

The COVID-19 pandemic is to escalate globally and acquire new mutations quickly, so accurate diagnostic technologies play a vital role in controlling and understanding the epidemiology of the disease. A plethora of technologies acquires diagnosis of individuals and informs clinical management of COVID. Some important biochemical parameters for COVID diagnosis are the elevation of liver enzymes, creatinine, and nonspecific inflammatory markers such as C-reactive protein (CRP) and Interleukin 6 (IL-6). The main progression predictors are lymphopenia, elevated D-dimer, and hyperferritinemia, although it is also necessary to consider LDH, CPK, and troponin in the marker panel of diagnosis. Owing to the greater sensitivity and accuracy, molecular technologies such as conventional polymerase chain reaction (PCR), reverse transcription (RT)-PCR, nested PCR, loop-mediated isothermal amplification (LAMP), and xMAP technology have been extensively used for COVID diagnosis for some time now. To make so many diagnostics accessible to general people, many techniques may be exploited, including point of care (POC), also called bedside testing, which is developing as a portable promising tool in pathogen identification. Some other lateral flow assay (LFA)-centered techniques like SHERLOCK, CRISPR-Cas12a (AIOD-CRISPR), and FNCAS9 editor limited uniform detection assay (FELUDA), etc. have shown auspicious results in the rapid detection of pathogens. More recently, low-cost sequencing and advancements in big data management have resulted in a slow but steady rise of next-generation sequencing (NGS)-based approaches for diagnosis that have potential relevance for clinical purposes and may pave the way toward a better future. Due to the COVID-19 pandemic, various institutions provided free, specialized websites and tools to promote research and access to critically needed advanced solutions by alleviating research and analysis of data within a substantial body of scientific and patent literature regarding biochemical and molecular diagnosis published since January 2020. This circumstance is unquestionably unique and difficult for anyone using patent information to find pertinent disclosures at a specific date in a trustworthy manner.

Nanoparticle-Based Bioaffinity Assays: From the Research Laboratory to the Market

Advances in the development of new biorecognition elements, nanoparticle-based labels as well as instrumentation have inspired the design of new bioaffinity assays. This review critically discusses the potential of nanoparticles to replace current enzymatic or molecular labels in immunoassays and other bioaffinity assays. Successful implementations of nanoparticles in commercial assays and the need for rapid tests incorporating nanoparticles in different roles such as capture support, signal generation elements, and signal amplification systems are highlighted. The limited number of nanoparticles applied in current commercial assays can be explained by challenges associated with the analysis of real samples (e.g., blood, urine, or nasal swabs) that are difficult to resolve, particularly if the same performance can be achieved more easily by conventional labels. Lateral flow assays that are based on the visual detection of the red-colored line formed by colloidal gold are a notable exception, exemplified by SARS-CoV-2 rapid antigen tests that have moved from initial laboratory testing to widespread market adaption in less than two years.

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

Biosensors with Boronic Acid-Based Materials as the Recognition Elements and Signal Labels

It is of great importance to have sensitive and accurate detection of cis-diol-containing biologically related substances because of their important functions in the research fields of metabolomics, glycomics, and proteomics. Boronic acids can specifically and reversibly interact with 1,2- or 1,3-diols to form five or six cyclic esters. Based on this unique property, boronic acid-based materials have been used as synthetic receptors for the specific recognition and detection of cis-diol-containing species. This review critically summarizes the recent advances with boronic acid-based materials as recognition elements and signal labels for the detection of cis-diol-containing biological species, including ribonucleic acids, glycans, glycoproteins, bacteria, exosomes, and tumor cells. We also address the challenges and future perspectives for developing versatile boronic acid-based materials with various promising applications.

Recent Advances in Quantum Dot-Based Lateral Flow Immunoassays for the Rapid, Point-of-Care Diagnosis of COVID-19

The COVID-19 pandemic has spurred demand for efficient and rapid diagnostic tools that can be deployed at point of care to quickly identify infected individuals. Existing detection methods are time consuming and they lack sensitivity. Point-of-care testing (POCT) has emerged as a promising alternative due to its user-friendliness, rapidity, and high specificity and sensitivity. Such tests can be conveniently conducted at the patient's bedside. Immunodiagnostic methods that offer the rapid identification of positive cases are urgently required. Quantum dots (QDs), known for their multimodal properties, have shown potential in terms of combating or inhibiting the COVID-19 virus. When coupled with specific antibodies, QDs enable the highly sensitive detection of viral antigens in patient samples. Conventional lateral flow immunoassays (LFAs) have been widely used for diagnostic testing due to their simplicity, low cost, and portability. However, they often lack the sensitivity required to accurately detect low viral loads. Quantum dot (QD)-based lateral flow immunoassays have emerged as a promising alternative, offering significant advancements in sensitivity and specificity. Moreover, the lateral flow immunoassay (LFIA) method, which fulfils POCT standards, has gained popularity in diagnosing COVID-19. This review focuses on recent advancements in QD-based LFIA for rapid POCT COVID-19 diagnosis. Strategies to enhance sensitivity using QDs are explored, and the underlying principles of LFIA are elucidated. The benefits of using the QD-based LFIA as a POCT method are highlighted, and its published performance in COVID-19 diagnostics is examined. Overall, the integration of quantum dots with LFIA holds immense promise in terms of revolutionizing COVID-19 detection, treatment, and prevention, offering a convenient and effective approach to combat the pandemic.

Simultaneous and Visual Detection of KPC and NDM Carbapenemase-Encoding Genes Using Asymmetric PCR and Multiplex Lateral Flow Strip

Carbapenem-resistant Enterobacteriaceae (CRE) infections constitute a threat to public health, and KPC and NDM are the major carbapenemases of concern. Rapid diagnostic tests are highly desirable in point-of-care (POC) and emergency laboratories with limited resources. Here, we developed a multiplex lateral flow assay based on asymmetric PCR and barcode capture probes for the simultaneous detection of KPC-2 and NDM-1. Biotinylated barcode capture probes corresponding to the KPC-2 and NDM-1 genes were designed and cast onto two different sensing zones of a nitrocellulose membrane after reacting with streptavidin to prepare a multiplex lateral flow strip. Streptavidin-coated gold nanoparticles (SA-AuNPs) were used as signal reporters. In response to the target carbapenemase genes, biotin-labelled ssDNA libraries were produced by asymmetric PCR, which bond to SA-AuNPs via biotin and hybridise with the barcode capture probe via a complementary sequence, thereby bridging SA-AuNPs and the barcode capture probe to form visible red lines on the detection zones. The signal intensities were proportional to the number of resistance genes tested. The strip sensor showed detection limits of 0.03 pM for the KPC-2 and 0.07 pM for NDM-1 genes, respectively, and could accurately distinguish between KPC-2 and NDM-1 genes in CRE strains. For the genotyping of clinical isolates, our strip exhibited excellent consistency with real-time fluorescent quantitative PCR and gene sequencing. Given its simplicity, cost-effectiveness, and rapid analysis accomplished by the naked eye, the multiplex strip is promising auxiliary diagnostic tool for KPC-2 and NDM-1 producers in routine clinical laboratories.

Lateral flow immunoassays for antigens, antibodies and haptens detection

Lateral flow immunoassay (LFIA) is widely used as a rapid point-of-care testing (POCT) technique in food safety, veterinary and clinical detection on account of the accessible, fast and low-cost characteristics. After the outbreak of the coronavirus disease 2019 (COVID-19), different types of LFIAs have attracted considerable interest because of their ability of providing immediate diagnosis directly to users, thereby effectively controlling the outbreak. Based on the introduction of the principles and key components of LFIAs, this review focuses on the major detection formats of LFIAs for antigens, antibodies and haptens. With the rapid innovation of detection technologies, new trends of novel labels, multiplex and digital assays are increasingly integrated with LFIAs. Therefore, this review will also introduce the development of new trends of LFIAs as well as its future perspectives.

A Review of Modern Methods for the Detection of Foodborne Pathogens

Despite the recent advances in food preservation techniques and food safety, significant disease outbreaks linked to foodborne pathogens such as bacteria, fungi, and viruses still occur worldwide indicating that these pathogens still constitute significant risks to public health. Although extensive reviews of methods for foodborne pathogens detection exist, most are skewed towards bacteria despite the increasing relevance of other pathogens such as viruses. Therefore, this review of foodborne pathogen detection methods is holistic, focusing on pathogenic bacteria, fungi, and viruses. This review has shown that culture-based methods allied with new approaches are beneficial for the detection of foodborne pathogens. The current application of immunoassay methods, especially for bacterial and fungal toxins detection in foods, are reviewed. The use and benefits of nucleic acid-based PCR methods and next-generation sequencing-based methods for bacterial, fungal, and viral pathogens' detection and their toxins in foods are also reviewed. This review has, therefore, shown that different modern methods exist for the detection of current and emerging foodborne bacterial, fungal, and viral pathogens. It provides further evidence that the full utilization of these tools can lead to early detection and control of foodborne diseases, enhancing public health and reducing the frequency of disease outbreaks.

Nanotechnology-Based Diagnostics for Diseases Prevalent in Developing Countries: Current Advances in Point-of-Care Tests

The introduction of point-of-care testing (POCT) has revolutionized medical testing by allowing for simple tests to be conducted near the patient's care point, rather than being confined to a medical laboratory. This has been especially beneficial for developing countries with limited infrastructure, where testing often involves sending specimens off-site and waiting for hours or days for results. However, the development of POCT devices has been challenging, with simplicity, accuracy, and cost-effectiveness being key factors in making these tests feasible. Nanotechnology has played a crucial role in achieving this goal, by not only making the tests possible but also masking their complexity. In this article, recent developments in POCT devices that benefit from nanotechnology are discussed. Microfluidics and lab-on-a-chip technologies are highlighted as major drivers of point-of-care testing, particularly in infectious disease diagnosis. These technologies enable various bioassays to be used at the point of care. The article also addresses the challenges faced by these technological advances and interesting future trends. The benefits of point-of-care testing are significant, especially in developing countries where medical care is shifting towards prevention, early detection, and managing chronic conditions. Infectious disease tests at the point of care in low-income countries can lead to prompt treatment, preventing infections from spreading.

Joint-detection of Salmonella typhimurium and Escherichia coli O157:H7 by an immersible amplification dip-stick immunoassay

To explore the superiority of multifunctional nanocomposites and realize the joint-detection of foodborne pathogens, an immersible amplification dip-stick immunoassay (DSIA) was exploited for the sensitive detection of Salmonella typhimurium (S. typhi) and Escherichia coli O157:H7 (E. coli O157:H7). Saving for the basic colorimetric performance, the reporter molecule of CoFe₂O₄ (CFO) possesses multivalent elements (Co^2+/3+, Fe^2+/3+) as well as multifunction of superior catalase-like activity and magnetic properties. By dint of the catalytic activity of CFO, a directly immersible amplification can be simply achieved to endure the DSIA with an intensive signal and a dual-visible mode for the determination of S. typhi and E. coli O157:H7. In virtue of the magnetic separation and enrichment capability of the CFO, the DSIA can perform a matrix-interference-free detection and obtain a dynamic detection range of 10²-10⁸ CFU/mL and a low assay limit of 10² CFU/mL. Moreover, the DSIA has reasonable recovery rates for contamination monitoring of two target bacteria in milk and beef samples. Our research provides a persuasive supplement for the application of multifunctional nanocomposites in the ongoing dip-stick immunoassay and an alternative strategy for the efficient detection of foodborne pathogens.

Effect of Selenium Nanoparticle Size on IL-6 Detection Sensitivity in a Lateral Flow Device

Sepsis is the body's response to an infection. Existing diagnostic testing equipment is not available in primary care settings and requires long waiting times. Lateral flow devices (LFDs) could be employed in point-of-care (POC) settings for sepsis detection; however, they currently lack the required sensitivity. Herein, LFDs are constructed using 150-310 nm sized selenium nanoparticles (SeNPs) and are compared to commercial 40 nm gold nanoparticles (AuNPs) for the detection of the sepsis biomarker interleukin-6 (IL-6). Both 310 and 150 nm SeNPs reported a lower limit of detection (LOD) than 40 nm AuNPs (0.1 ng/mL compared to 1 ng/mL), although at the cost of test line visual intensity. This is to our knowledge the first use of larger SeNPs (>100 nm) in LFDs and the first comparison of the effect of the size of SeNPs on assay sensitivity in this context. The results herein demonstrate that large SeNPs are viable alternatives to existing commercial labels, with the potential for higher sensitivity than standard 40 nm AuNPs.

Lateral flow assays for detection of disease biomarkers

Early diagnosis saves lives in many diseases. In this sense, monitoring of biomarkers is crucial for the diagnosis of diseases. Lateral flow assays (LFAs) have attracted great attention among paper-based point-of-care testing (POCT) due to their low cost, user-friendliness, and time-saving advantages. Developments in the field of health have led to an increase of interest in these rapid tests. LFAs are used in the diagnosis and monitoring of many diseases, thanks to biomarkers that can be observed in body fluids. This review covers the recent advances dealing with the design and strategies for the development of LFA for the detection of biomarkers used in clinical applications in the last 5 years. We focus on various strategies such as choosing the nanoparticle type, single or multiple test approaches, and equipment for signal transducing for the detection of the most common biomarkers in different diseases such as cancer, cardiovascular, infectious, and others including Parkinson's and Alzheimer's diseases. We expect that this study will contribute to the different approaches in LFA and pave the way for other clinical applications.

Development of carbon nanoparticles-based soluble solid-phase immune sensor for the quantitative diagnosis of inflammation

Quantitative immunodiagnosis is one of the most commonly used methods for in vitro diagnostics. Various bioanalytical methods have been developed to quantitatively diagnose immune analytes; however, they require blood dilution pretreatment, reaction mixing, complicated experimental steps, and can cause diagnostic errors due to the hook effect. To address this issue, we introduced a simple immunoassay based on carbon nanoparticles (CNPs). The assay was designed to have high flexibility for use in various in vitro diagnostic devices by constructing a soluble solid-phase immune sensor with high solubility using antibody-conjugated CNPs and polymer materials. Excellent performance was achieved using a free-antibody system with dual calibration. To verify the performance of this method with high reliability, canine C-reactive protein was selected as the immune analyte. Interestingly, our method efficiently mitigated the hook effect with outstanding performance in a one-step reaction without blood dilution or reaction mixing. The detection range of the target can be effectively controlled using free antibodies. Therefore, our CNP-based immunodiagnosis method may advance the commercialization of point-of-care immune biosensors.

A Comprehensive Study: Traditional and Cutting-Edge Analytical Techniques for the Biomarker Based Detection of the Micronutrients & POC Sensing Directions for Next-Generation Diagnostic

Micronutrient deficiency is wide spread and highly affects morbidity, mortality, and well-being of human beings. Micronutrient deficiency gradually manifests into diseases, which effects pathophysiology directly or indirectly. There is an imprecision in the diagnosis of micronutrient deficiency because of two causes; the selection of the standard biomarker and the diagnostic technique used. In appropriate diagnosis could increase the severity of the disorder. Instead of a single a combination of biomarkers can give more stringent results for micronutrient testing. Several traditional analytical techniques are used for diagnosis but HPLC, ELISA & LCMS/MS are most sensitive and reliable methods used by CLSIA-certified labs. However, these techniques require well-equipped, centralized laboratory facilities. The diagnostic era moves toward the Point of Care Testing (POCT), a boon in emerging diagnostics, breaking all paradigms of traditional analytical techniques. POCT led us toward the development of biosensors, which encompasses many techniques like paper-based sensors, microfluidic chip, wearable devices, and smartphone-assisted diagnostics, which become more popular diagnostic tools. This outlook summarizes the micronutrients like vitamins A, B5, B6, B7, B9, B12 C, D, and E and Minerals like iron, calcium, zinc, magnesium, and sodium; along with its biomarkers, analytical techniques, and point of care innovation in micronutrients.

Recent advances in immunoassay technologies for the detection of human coronavirus infections

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the seventh coronavirus (CoV) that has spread in humans and has become a global pandemic since late 2019. Efficient and accurate laboratory diagnostic methods are one of the crucial means to control the development of the current pandemic and to prevent potential future outbreaks. Although real-time reverse transcription-polymerase chain reaction (rRT-PCR) is the preferred laboratory method recommended by the World Health Organization (WHO) for diagnosing and screening SARS-CoV-2 infection, the versatile immunoassays still play an important role for pandemic control. They can be used not only as supplemental tools to identify cases missed by rRT-PCR, but also for first-line screening tests in areas with limited medical resources. Moreover, they are also indispensable tools for retrospective epidemiological surveys and the evaluation of the effectiveness of vaccination. In this review, we summarize the mainstream immunoassay methods for human coronaviruses (HCoVs) and address their benefits, limitations, and applications. Then, technical strategies based on bioinformatics and advanced biosensors were proposed to improve the performance of these methods. Finally, future suggestions and possibilities that can lead to higher sensitivity and specificity are provided for further research.

Visual and rapid identification of Chlamydia trachomatis and Neisseria gonorrhoeae using multiplex loop-mediated isothermal amplification and a gold nanoparticle-based lateral flow biosensor

Sexually transmitted chlamydia and gonorrhea infections caused by the bacteria Chlamydia trachomatis and Neisseria gonorrhoeae remain a major public health concern worldwide, particularly in less developed nations. It is crucial to use a point of care (POC) diagnostic method that is quick, specific, sensitive, and user-friendly to treat and control these infections effectively. Here, a novel molecular diagnostic assay, combining multiplex loop-mediated isothermal amplification (mLAMP) with a visual gold nanoparticles-based lateral flow biosensor (AuNPs-LFB) was devised and used for highly specific, sensitive, rapid, visual, and easy identification of C. trachomatis and N. gonorrhoeae. Two unique independent primer pairs were successful designed against the ompA and orf1 genes of C. trachomatis and N. gonorrhoeae, respectively. The optimal mLAMP-AuNPs-LFB reaction conditions were determined to be 67°C for 35 min. The detection procedure, involving crude genomic DNA extraction (~5 min), LAMP amplification (35 min), and visual results interpretation (<2 min), can be completed within 45 min. Our assay has a detection limit of 50 copies per test, and we did not observe any cross-reactivity with any other bacteria in our testing. Hence, our mLAMP-AuNPs-LFB assay can potentially be used for POC testing to detect C. trachomatis and N. gonorrhoeae in clinical settings, particularly in underdeveloped regions.

Flow-Based Chemiluminescence Microarrays as Screening Platform for Affinity Binders to Capture and Elute Bacteria

Affinity describes the non-covalent but selective interaction between an affinity binder (e.g., proteins, antibiotics, or antibodies) and its counterpart (e.g., bacteria). These affinity binders can serve to detect bacteria and respond to the need for selective concentration via affinity chromatography for trace analysis. By changing the pH value or salt and protein contents, affinity bindings can be reversed, and bacteria can be recovered for characterisation. Analytical microarrays use multiple affinity binders immobilised on the surface in a distinct pattern, which immensely reduces screening time for the discovery of superior binding motifs. Here, flow-based microarray systems can inform not only about binding, but also about desorption. In this work, we pioneer a screening assay for affinity binders against both gram-positive and negative bacteria based on an automated flow-based chemiluminescence (CL) microarray. Biotinylation of model organisms E. coli and E. faecalis enabled labelling with horseradish-peroxidase-coupled streptavidin, and detection with CL. Polymyxin B, an antibiotic against gram-negative bacteria, was found to bind both E. coli and E. faecalis. Simultaneous screening for desorption methods unexpectedly revealed methyl alpha-D-mannopyranoside as a promising buffer for desorption from Polymyxin B. This proof-of-principle study shows that our new platform greatly facilitates the screening of new affinity binders against bacteria, with promise for future automation.

Absorption-Modulated SiO2@Au Core-Satellite Nanoparticles for Highly Sensitive Detection of SARS-CoV-2 Nucleocapsid Protein in Lateral Flow Immunosensors

The worldwide spread of coronavirus disease 2019 (COVID-19) highlights the need for rapid, simple, and accurate tests to detect various variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The antigen test, based on the lateral flow immunoassay (LFI), is a suitable "first line of defense" test that enables early identification and timely isolation of patients to minimize viral transmission among communities. However, it is generally less accurate than nucleic acid testing, and its sensitivity needs improvement. Here, a novel rapid detection method is designed to sensitively detect SARS-CoV-2 using isolated gold nanoparticle (AuNP)-assembled SiO2 core-satellite nanoparticles (SiO2@Au CSNPs). Well-grown AuNP satellites in the synthesis of SiO2@Au CSNPs significantly enhanced their light absorption, increased the detection sensitivity, and lowered the detection limit by 2 orders of magnitude relative to conventional gold colloids. The proposed system enabled highly sensitive detection of the SARS-CoV-2 nucleocapsid protein with a detection limit of 0.24 pg mL-1 within 20 min. This is the first study to develop a highly sensitive antigen test using the absorption-modulated SiO2@Au CSNPs. Our findings demonstrate the capacity of this platform to serve as an effective sensing strategy for managing pandemic conditions and preventing the spread of viral infections.

Sensitive and visual identification of Chlamydia trachomatis using multiple cross displacement amplification integrated with a gold nanoparticle-based lateral flow biosensor for point-of-care use

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infection (STI) and remains a major public health challenge, especially in less-developed regions. Establishing a rapid, inexpensive, and easy-to-interpret point-of-care (POC) testing system for C. trachomatis could be critical for its treatment and limiting further transmission. Here, we devised a novel approach termed a multiple cross displacement amplification integrated with gold nanoparticle-based lateral flow biosensor (MCDA-AuNPs-LFB) for the highly specific, sensitive, user-friendly, and rapid identification of C. trachomatis in clinical samples. A suite of MCDA primers based on the C. trachomatis ompA gene from 14 serological variants (serovar A-K, L1, L2, and L3) were successfully designed and used to establish the assay. Optimal assay conditions were identified at 67°C, and the detection procedure, including nucleic acid preparation (approximately 5 min), MCDA amplification (30 min), and AuNPs-LFB visual readout (within 2 min), was completed within 40 min. The all-in cost for each test was approximately $5.5 USD. The limit of detection (LoD) was 10 copies/reaction, and no cross-reaction was observed with non-C. trachomatis microbes. A total of 135 suspected C. trachomatis-infection genital secretion samples were collected and simultaneously detected using real-time quantitative PCR (qPCR) in our assay. Compared with the qPCR technology, the MCDA-AuNPs-LFB sensitivity, specificity, positive predictive value, and negative predictive value were 100%, 96.20%, 94.92%, and 100%, respectively. Hence, our MCDA-AuNP-LFB assay exhibited considerable potential for POC testing and could be used to identify C. trachomatis in clinical settings, particularly in low-income regions.

Paper-based genetic assays with bioconjugated gold nanorods and an automated readout pipeline

Paper-based biosensors featuring immunoconjugated gold nanoparticles have gained extraordinary momentum in recent times as the platform of choice in key cases of field applications, including the so-called rapid antigen tests for SARS-CoV-2. Here, we propose a revision of this format, one that may leverage on the most recent advances in materials science and data processing. In particular, we target an amplifiable DNA rather than a protein analyte, and we replace gold nanospheres with anisotropic nanorods, which are intrinsically brighter by a factor of ~ 10, and multiplexable. By comparison with a gold-standard method for dot-blot readout with digoxigenin, we show that gold nanorods entail much faster and easier processing, at the cost of a higher limit of detection (from below 1 to 10 ppm in the case of plasmid DNA containing a target transgene, in our current setup). In addition, we test a complete workflow to acquire and process photographs of dot-blot membranes with custom-made hardware and regression tools, as a strategy to gain more analytical sensitivity and potential for quantification. A leave-one-out approach for training and validation with as few as 36 sample instances already improves the limit of detection reached by the naked eye by a factor around 2. Taken together, we conjecture that the synergistic combination of new materials and innovative tools for data processing may bring the analytical sensitivity of paper-based biosensors to approach the level of lab-grade molecular tests.

A new dynamic deep learning noise elimination method for chip-based real-time PCR

Point-of-care (POC) real-time polymerase chain reaction (PCR) has become one of the most important technologies for many fields such as pathogen detection and water-quality monitoring. POC real-time PCR usually adopts chips with small-volume chambers for portability, which is more likely to produce complex noise that seriously affects the accuracy. Such complex noises are difficult to be eliminated by the traditional fixed area algorithm that is most commonly used at present because they usually have random shape, location, and brightness. To address this problem, we proposed a novel image analysis method, Dynamic Deep Learning Noise Elimination Method (DIPLOID), in this paper. Our new method could recognize and output the mask of the interference by Mask R-CNN, and then subtract the interference and select the maximum valid contiguous area for brightness analysis by dynamic programming. Compared with the traditional method, DIPLOID increased the accuracy, sensitivity, and specificity from 57.9 to 94.6%, 49.1 to 93.9%, and 65.9 to 95.2%, respectively. DIPLOID has great anti-interference, robustness, and sensitivity, which can reduce the impact of complex noise as much as possible from the aspect of the algorithm. As shown in the experiments of this paper, our method significantly improved the accuracy to over 94% under the complex noise situation, which could make the POC real-time PCR have greater potential in the future.

An abiotic fluorescent probe for the detection and quantification of carcinoembryonic antigen

The reported methods mainly use biomolecules such as antibodies, enzymes, and aptamers for biomarker detection. However, applying an abiotic fluorescent probe to detect cancer biomarkers such as carcinoembryonic antigen (CEA) has not been reported. In this regard, we conceived an abiotic fluorescent probe BIQ-1 for the rapid yet straightforward detection of CEA. The bioinformatics tools and molecular docking techniques were used to develop the probe BIQ-1 for the selective detection and quantification of CEA in a buffer matrix resembling serum. The probe BIQ-1 exhibited a limit of detection of 0.2 ng/mL for CEA in a simple cuvette-based experiment. The BIQ-1 did no show interference from the possible interfering components such as hemoglobin, intralipid, and human serum albumin (HSA) in concentrations several-fold higher (µg/mL) than CEA.

High sensitivity and rapid detection of hepatitis B virus DNA using lateral flow biosensors based on Au@Pt nanorods in the absence of hydrogen peroxide

Au@Pt nanorods with enhanced oxidase-like activity were designed and used as signal probes to construct LFBs for the high sensitivity detection of hepatitis B virus DNA (HBV-DNA).

Design of multiplexing lateral flow immunoassay for detection and typing of foot-and-mouth disease virus using pan-reactive and serotype-specific monoclonal antibodies: Evidence of a new hook effect

The foot-and-mouth disease (FMD) is the most important transboundary viral disease of livestock in the international context, because of its extreme contagiousness, widespread diffusion, and severe impact on animal trade and animal productions. The rapid and on-field detection of the virus responsible for the FMD represents an urgent demand to efficiently control the diffusion of the infection, especially in low resource setting where the FMD is endemic. Colorimetric lateral flow immunoassay (LFIA) is largely used for the development of rapid tests, due to the extreme simplicity, cost-effectiveness, and on-field operation. In this work, two multiplex LFIA devices were designed for the diagnosis of FMD and the simultaneous identification of major circulating serotypes of the FMD virus. The LFIAs relied on the sandwich-type immunoassay and combined a set of well-characterised monoclonal antibodies (mAb) pairs. One LFIA aimed at detecting and identifying O, A and Asia-1 serotypes, the second device enabled the detection and differentiation of the SAT 1 and SAT 2 serotypes. Both devices also incorporated a broad-specific test line reporting on infection from FMDV, regardless the strain and the serotype involved. Accordingly, five and four reactive zones were arranged in the two devices to achieve a total of six simultaneous analyses. The development of the two multiplex systems highlighted for the first time the relevance of the mAb positioning along the LFIA strip in connection with the use of the same or different mAb as capture and detector ligands. In fact, the excess of detector mAb typically employed for increasing the sensitivity of sandwich immunoassay induced a new type of hook effect when combined with the same ligand used as the capture. This effect strongly impacted assay sensitivity, which could be improved by an intelligent alignment of the mAb pairs along the LFIA strip. The analytical and diagnostic performances of the two LFIAs were studied by testing reference FMDV strains grown in cell cultures and some representative field samples (epithelium homogenates). Almost equivalent sensitivity and specificity to those of a reference Ag-ELISA kit were shown, except for the serotype SAT 2. These simple devices are suitable in endemic regions for in-field diagnosis of FMD accompanied by virus serotyping and, moreover, could be deployed and used for rapid confirmation of secondary outbreaks after FMD incursions in free-areas, thus contributing to promptly implement control measures.

Biosensor Technologies in Medicine: from Detection of Biochemical Markers to Research into Molecular Targets (Review)

Infections are a major cause of premature death. Fast and accurate laboratory diagnostics of infectious diseases is a key condition for the timely initiation and success of treatment. Potentially, it can reduce morbidity, as well as prevent the outbreak and spread of dangerous epidemics. The traditional methods of laboratory diagnostics of infectious diseases are quite time- and labour-consuming, require expensive equipment and trained personnel, which is crucial within limited resources. The fast biosensor-based methods that combine the diagnostic capabilities of biomedicine with modern technological advances in microelectronics, optoelectronics, and nanotechnology make an alternative.

The modern achievements in the development of label-free biosensors make them promising diagnostic tools that combine rapid detection of specific molecular markers, simplicity, ease-of-use, efficiency, accuracy, and cost-effectiveness with the tendency to the development of portable platforms. These qualities exceed the generally accepted standards of microbiological and immunological diagnostics and open up broad prospects for using these analytical systems in clinical practice directly at the site of medical care provision (point-of-care, POC concept).

A wide variety of modern biosensor designs are based on the use of diverse formats of analytical and technological strategies, identification of various regulatory and functional molecular markers associated with infectious pathogens. The solution to the existing problems in biosensing will open up great prospects for these rapidly developing diagnostic biotechnologies.

SARS-CoV-2 and approaches for a testing and diagnostic strategy

The COVID-19 pandemic has led to an unprecedented global health challenge, creating sudden, massive demands for diagnostic testing, treatment, therapies, and vaccines. In particular, the development of diagnostic assays for SARS-CoV-2 has been pursued as they are needed for quarantine, disease surveillance, and patient treatment. One of the major lessons the pandemic highlighted was the need for fast, cheap, scalable and reliable diagnostic methods, such as paper-based assays. Furthermore, it has previously been suggested that paper-based tests may be more suitable for settings with lower resource availability and may help alleviate some supply chain challenges which arose during the COVID-19 pandemic. Therefore, we explore how such devices may fit in a comprehensive diagnostic strategy and how some of the challenges to the technology, e.g. low sensitivity, may be addressed. We discuss the properties of the SARS-CoV-2 virus itself, the COVID-19 disease pathway, and the immune response. We then describe the different diagnostic strategies that have been pursued, focusing on molecular strategies for viral genetic material, antigen tests, and serological assays, and innovations for improving the diagnostic sensitivity and capabilities. Finally, we discuss pressing issues for the future, and what needs to be addressed for the ongoing pandemic and future outbreaks.

Blind Spot: A Braille Patterned Novel Multiplex Lateral Flow Immunoassay Sensor Array for the Detection of Biothreat Agents

Lateral flow immunoassays (LFIs) are simple, point-of-care diagnostic devices used for detecting biological agents or other analytes of interest in a sample. LFIs are predominantly singleplex assays, interrogating one target analyte at a time. There is a need for multiplex LFI devices, e.g., a syndromic panel to differentiate pathogens causing diseases exhibiting similar symptoms. Multiplex LFI devices would be especially valuable in instances where sample quantity is limiting and reducing assay time and costs is critical. There are limitations to the design parameters and performance characteristics of a multiplex LFI assay with many horizontal test lines due to constraints in capillary flow dynamics. To address some of the performance issues, we have developed a spot array multiplex LFI using Braille format (hence called Blind Spot) and a sensor, MACAW (Modular Automated Colorimetric Analyses Widget), that can analyze and interpret the results. As a proof of concept, we created a multiplex toxin panel, for detecting three toxins, using two letter codes for each. The results indicated that the six-plex, triple toxin assay performs as well as singleplex assays. The sensor-based calls are better compared to human interpretation in discriminating and interpreting ambiguous test results correctly especially at lower antigen concentrations and from strips with blemishes.

Aptamer-based lateral flow assay on-site biosensors

The lateral flow assay (LFA) is a widely used paper-based on-site biosensor that can detect target analytes and obtain test results in several minutes. Generally, antibodies are utilized as the biorecognition molecules in the LFA. However, antibodies selected using an in vivo process not only may risk killing the animal hosts and causing errors between different batches but also their range is restricted by the refrigerated conditions used to store them. To avoid these limitations, aptamers screened by an in vitro process have been studied as biorecognition molecules in LFAs. Based on the sandwich or competitive format, the aptamer-based LFA can accomplish on-site detection of target analytes. Since aptamers have a distinctive ability to undergo conformational changes, the adsorption-desorption format has also been exploited to detect target analytes in aptamer-based LFAs. This paper reviews developments in aptamer-based LFAs in the last three years for the detection of target analytes. Three formats of aptamer-based LFAs, i.e., sandwich, competitive, and adsorption-desorption, are described in detail. Based on these formats, signal amplification strategies and multiplexed detection are discussed in order to provide an overview of aptamer-based LFAs for on-site detection of target analytes. In addition, the potential commercialization and future perspectives of aptamer-based LFAs for rapid detection of SARS-CoV-2 are given to support the COVID-19 pandemic.

A Pencil-Drawn Electronic Tongue for Environmental Applications

We report on the development of a simple and cost-effective potentiometric sensor array that is based on manual “drawing” on the polymeric support with the pencils composed of graphite and different types of zeolites. The sensor array demonstrates distinct sensitivity towards a variety of inorganic ions in aqueous media. This multisensor system has been successfully applied to quantitative analysis of 100 real-life surface waters sampled in Mahananda and Hooghly rivers in the West Bengal state (India). Partial least squares regression has been utilized to relate responses of the sensors to the values of different water quality parameters. It has been found that the developed sensor array, or electronic tongue, is capable of quantifying total hardness, total alkalinity, and calcium content in the samples, with the mean relative errors below 18%.

Sensitive and Easy-Read CRISPR Strip for COVID-19 Rapid Point-of-Care Testing

Rapid and clinically sensitive detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) play an important role in the contact tracing and containment of the COVID-19 pandemic. A recently developed field-deployable clustered regularly interspaced short palindromic repeats (CRISPR) detection assay with lateral flow strips shows promise for point-of-care detection of SARS-CoV-2. However, the limit of detection of paper strip-based assays (10-100 copies/μL) is much lower than that of fluorescence-based detection methods. In this study, we developed an easy-readout and sensitive enhanced (ERASE) strip to visualize the results of CRISPR detection and improve the sensitivity to 1 copy/μL with an unambiguous easy-read result. Using 649 clinical samples from blind specimens collected from patients in China, we validated our ERASE assay for SARS-CoV-2 RNA detection with 90.67% positive predictive agreement and 99.21% negative predictive agreement. In conclusion, our study provided a customized CRISPR strip for use in a simple, rapid, ultrasensitive, and highly specific assay for SARS-CoV-2 detection. (Clinical Trial Registration number: 2020-008-01; [2020]IEC(ZD01); PJ-NBEY-2020-009-01; 2020#34).

Low-Cost Optical Assays for Point-of-Care Diagnosis in Resource-Limited Settings

Readily deployable, low-cost point-of-care medical devices such as lateral flow assays (LFAs), microfluidic paper-based analytical devices (μPADs), and microfluidic thread-based analytical devices (μTADs) are urgently needed in resource-poor settings. Governed by the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverability) set by the World Health Organization, these reliable platforms can screen a myriad of chemical and biological analytes including viruses, bacteria, proteins, electrolytes, and narcotics. The Ebola epidemic in 2014 and the ongoing pandemic of SARS-CoV-2 have exemplified the ever-increasing importance of timely diagnostics to limit the spread of diseases. This review provides a comprehensive survey of LFAs, μPADs, and μTADs that can be deployed in resource-limited settings. The subsequent commercialization of these technologies will benefit the public health, especially in areas where access to healthcare is limited.

Polystyrene Microsphere-Based Immunochromatographic Assay for Detection of Aflatoxin B1 in Maize

Aflatoxin B1 (AFB1), a mycotoxin, is hepatotoxic, carcinogenic, and nephrotoxic in humans and animals, and contaminate a wide range of maize. In this study, an immunochromatographic assay (ICA) based on polystyrene microspheres (PMs) was developed for sensitive and quantitative detection of AFB1 in maize. The amounts of PMs, the condition for activating carboxyl groups of PMs, the amount of monoclonal antibody (mAb), and the volume of the immune probe were optimized to enhance the performance PMs-ICA for point-of-care testing of AFB1 in maize. The PMs-ICA showed the cut-off value of 1 ng/mL in phosphate buffer (PB) and 6 µg/kg in maize samples, respectively. The quantitative limit of detection (qLOD) was 0.27 and 1.43 µg/kg in PB and maize samples, respectively. The accuracy and precision of the PMs-ICA were evaluated by analysis of spiked maize samples with recoveries of 96.0% to 107.6% with coefficients of variation below 10%. In addition, the reliability of PMs-ICA was confirmed by the liquid chromatography-tandem mass spectrometry method. The results indicated that the PMs-ICA could be used as a sensitive, simple, rapid point-of-care testing of AFB1 in maize.

Challenge of diagnosing acute infections in poor resource settings in Africa

Frequent disease outbreaks and acute infections occur in rural and low-income urban areas of Africa, with many health systems unprepared to diagnose and control diseases that are recurrent, endemic or have extended their geographic zone. In this review, we focus on acute infections that can be characterized by sudden onset, rapid progression, severe symptoms and poor prognosis. Consequently, these infections require early diagnosis and intervention. While effective vaccines have been developed against some of these diseases, lack of compliance and accessibility, and the need for repeated or multiple vaccinations mean large populations can remain vulnerable to infection. It follows that there is a need for enhancement of national surveillance and diagnostic capacity to avert morbidity and mortality from acute infections. We discuss the limitations of traditional diagnostic methods and explore the relative merits and applicability of protein-, carbohydrate- and nucleic acid-based rapid diagnostic tests that have been trialled for some infectious diseases. We also discuss the utility and limitations of antibody-based serological diagnostics and explore how systems biology approaches can better inform diagnosis. Lastly, given the complexity and high cost associated with after-service support of emerging technologies, we propose that, for resource-limited settings in Africa, multiplex point-of-care diagnostic tools be tailor-made to detect both recurrent acute infections and endemic infections.

A single snapshot multiplex immunoassay platform utilizing dense test lines based on engineered beads

Co-circulation of coronavirus disease 2019 (COVID-19) and dengue fever has been reported. Accurate and timely multiplex diagnosis is required to prevent future pandemics. Here, we developed an innovative microfluidic chip that enables a snapshot multiplex immunoassay for timely on-site response and offers unprecedented multiplexing capability with an operating procedure similar to that of lateral flow assays. An open microchannel assembly of individually engineered microbeads was developed to construct nine high-density test lines, which can be imaged in a 1 mm² field-of-view. Thus, simultaneous detection of multiple antibodies would be achievable in a single high-resolution snapshot. Next, we developed a novel pixel intensity-based imaging process to distinguish effective and non-specific fluorescence signals, thereby improving the reliability of this fluorescence-based immunoassay. Finally, the chip specifically identified and classified random combinations of arbovirus (Zika, dengue, and chikungunya viruses) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies within 30 min. Therefore, we believe that this snapshot multiplex immunoassay chip is a powerful diagnostic tool to control current and future pandemics.

Pre-clinically evaluated visual lateral flow platform using influenza A and B nucleoprotein as a model and its potential applications

A visual colorimetric rapid screening system based on a lateral flow device for simultaneous detection and differentiation between influenza A and B nucleoprotein as a model was developed. Monoclonal antibodies, specific for either influenza A or B nucleoproteins, were evaluated for their reactivities and were used as targeting ligands. With the best antibody pairs selected, the system exhibited good specificity to both viruses without cross reactivity to other closely related respiratory viruses. Further semi-quantitative analysis using a strip reader revealed that the system is capable of detecting influenza A and B protein content as low as 0.04 and 1 ng per test, respectively, using a sample volume as low as 100 μL, within 10 minutes (R² = 0.9652 and 0.9718). With a performance comparison to the commercial tests, the system demonstrated a four-to-eight-fold higher sensitivity. Pre-clinical evaluation with 101 nasopharyngeal swabs reveals correlated results with a standard molecular approach, with 89% and 83% sensitivity towards influenza A and B viruses, and 100% specificity for both viruses.

Visual colorimetric rapid screening system based on lateral flow device for influenza A and B virus detection as a model and its pre-clinical evaluation.

SERS Based Lateral Flow Immunoassay for Point-of-Care Detection of SARS-CoV-2 in Clinical Samples

The current scenario, an ongoing pandemic of COVID-19, places a dreadful burden on the healthcare system worldwide. Subsequently, there is a need for a rapid, user-friendly, and inexpensive on-site monitoring system for diagnosis. The early and rapid diagnosis of SARS-CoV-2 plays an important role in combating the outbreak. Although conventional methods such as PCR, RT-PCR, and ELISA, etc., offer a gold-standard solution to manage the pandemic, they cannot be implemented as a point-of-care (POC) testing arrangement. Moreover, surface-enhanced Raman spectroscopy (SERS) having a high enhancement factor provides quantitative results with high specificity, sensitivity, and multiplex detection ability but lacks in POC setup. In contrast, POC devices such as lateral flow immunoassay (LFIA) offer rapid, simple-to-use, cost-effective, reliable platform. However, LFIA has limitations in quantitative and sensitive analyses of SARS-CoV-2 detection. To resolve these concerns, herein we discuss a unique modality that is an integration of SERS with LFIA for quantitative analyses of SARS-CoV-2. The miniaturization ability of SERS-based devices makes them promising in biosensor application and has the potential to make a better alternative of conventional diagnostic methods. This review also demonstrates the commercially available and FDA/ICMR approved LFIA kits for on-site diagnosis of SARS-CoV-2.

A site-specific DNA methylation biosensor for both visual and magnetic determination based on lateral flow assay

Tumorigenesis driven by abnormal DNA methylation has highlighted the need to develop a portable, rapid and sensitive strategy for accurate methylation detection with a specific cancer-prognostic gene, which caters to the popularization of precision medicine. In this study, a site-specific biosensor for both visual and magnetic DNA methylation determination has been established based on lateral flow assay. By introducing digoxin- and biotin-labeled primers into PCR, the amplicons can be recognized and captured by gold magnetic nanoparticles (GMNPs) in this biosensor. Working as a signal probe, the optical property of GMNPs allows the amplicons to be interpreted with naked eyes avoiding any complex equipment and cumbersome operation after PCR. Moreover, by virtue of the magnetic property of GMNP, the signal can be explained and recorded by a magnetometer in clinical practice. The introduction of tailor-made primer sets makes it possible to accurately distinguish 0.1% methylated variants in the presence of numerous unmethylated variants as strong interferential background and vice versa at target cytosine-guanine dinucleotide. A distinct signal can be observed with as low as 0.01 pg variants for both visual and magnetic analyses. As a significant tumor suppressor gene, the promoter methylation status of miR-34a is accurately determined with not only cell lines but also with clinical samples, which demonstrates the great potential of this biosensor for cancer diagnosis and prognosis.

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.

3D Hierarchical Nanotopography for On-Site Rapid Capture and Sensitive Detection of Infectious Microbial Pathogens

Effective capture and rapid detection of pathogenic bacteria causing pandemic/epidemic diseases is an important task for global surveillance and prevention of human health threats. Here, we present an advanced approach for the on-site capture and detection of pathogenic bacteria through the combination of hierarchical nanostructures and a nuclease-responsive DNA probe. The specially designed hierarchical nanocilia and network structures on the pillar arrays, termed 3D bacterial capturing nanotopographical trap, exhibit excellent mechanical reliability and rapid (<30 s) and irreversible bacterial capturability. Moreover, the nuclease-responsive DNA probe enables the highly sensitive and extremely fast (<1 min) detection of bacteria. The bacterial capturing nanotopographical trap (b-CNT) facilitates the on-site capture and detection of notorious infectious pathogens (Escherichia coli O157:H7, Salmonella enteritidis, Staphylococcus aureus, and Bacillus cereus) from kitchen tools and food samples. Accordingly, the usefulness of the b-CNT is confirmed as a simple, fast, sensitive, portable, and robust on-site capture and detection tool for point-of-care testing.

Ultrasensitive and Highly Specific Lateral Flow Assays for Point-of-Care Diagnosis

Lateral flow assays (LFAs) are paper-based point-of-care (POC) diagnostic tools that are widely used because of their low cost, ease of use, and rapid format. Unfortunately, traditional commercial LFAs have significantly poorer sensitivities (μM) and specificities than standard laboratory tests (enzyme-linked immunosorbent assay, ELISA: pM-fM; polymerase chain reaction, PCR: aM), thus limiting their impact in disease control. In this Perspective, we review the evolving efforts to increase the sensitivity and specificity of LFAs. Recent work to improve the sensitivity through assay improvement includes optimization of the assay kinetics and signal amplification by either reader systems or additional reagents. Together, these efforts have produced LFAs with ELISA-level sensitivities (pM-fM). In addition, sample preamplification can be applied to both nucleic acids (direct amplification) and other analytes (indirect amplification) prior to LFA testing, which can lead to PCR-level (aM) sensitivity. However, these amplification strategies also increase the detection time and assay complexity, which inhibits the large-scale POC use of LFAs. Perspectives to achieve future rapid (<30 min), ultrasensitive (PCR-level), and "sample-to-answer" POC diagnostics are also provided. In the case of LFA specificity, recent research efforts have focused on high-affinity molecules and assay optimization to reduce nonspecific binding. Furthermore, novel highly specific molecules, such as CRISPR/Cas systems, can be integrated into diagnosis with LFAs to produce not only ultrasensitive but also highly specific POC diagnostics. In summary, with continuing improvements, LFAs may soon offer performance at the POC that is competitive with laboratory techniques while retaining a rapid format.

Paper-based multiplex analytical device for simultaneous detection of Clostridioides difficile toxins and glutamate dehydrogenase

We report a new paper-based multiplex analytical device (mPAD) for simultaneous screening of three analytes (glutamate dehydrogenase, toxin A, and toxin B) known as biomarkers for Clostridioides difficile infection (CDI). To overcome the limitation of common rapid assays (e.g. lateral flow immunochromatographic and enzyme immunoassays) in terms of multiplexing, sensitivity, simplicity, and ease-of-use, the mPAD is constructed with a three dimensional (3D) configuration of paper components with a multi-channel design. Multiple fluidic paths developed with wax-patterned paper allow the simultaneous detection of glutamate dehydrogenase, toxin A, and toxin B without any cross-reactivity. The 3D fluidic network on the mPAD facilitates a self-operating test procedure for the mixing and addition of amplification reagents with a one-step sliding operation. The results of the multiplex CDI assay can be easily interpreted by the naked eye within 10 min, and are visually intensified over time resulting in up to 3-fold signal amplification. Our device exhibited remarkable analytical performances for the simultaneous detection of three CDI biomarkers, providing a sensitivity of 97%, specificity of 88%, accuracy of 95%, and limits of detection for glutamate dehydrogenase, toxin A, and toxin B of 0.16 ng mL^-1, 0.09 ng mL^-1, and 0.03 ng mL^-1, respectively. These results indicate the high applicability and feasibility of mPAD for multiplex testing for CDI with the advantages of being simple, sensitive, inexpensive, user-friendly, and equipment-free.

Current Status of Clinical Application of Point-of-Care Testing

CONTEXT.—

The clinical applications of point-of-care testing (POCT) are gradually increasing in many health care systems. Recently, POCT devices using molecular genetic method techniques have been developed. We need to examine clinical pathways to see where POCT can be applied to improve them.

OBJECTIVE.—

To introduce up-to-date POCT items and equipment and to provide the content that should be prepared for clinical application of POCT.

DATA SOURCES.—

Literature review based on PubMed searches containing the terms point-of-care testing, clinical chemistry, diagnostic hematology, and clinical microbiology.

CONCLUSIONS.—

If medical resources are limited, POCT can help clinicians make quick medical decisions. As POCT technology improves and menus expand, areas where POCT can be applied will also increase. We need to understand the limitations of POCT so that it can be optimally used to improve patient management.

A Portable Magnetic Particle Spectrometer for Future Rapid and Wash-Free Bioassays

Nowadays, there is an increasing demand for more accessible routine diagnostics for patients with respect to high accuracy, ease of use, and low cost. However, the quantitative and high accuracy bioassays in large hospitals and laboratories usually require trained technicians and equipment that is both bulky and expensive. In addition, the multistep bioassays and long turnaround time could severely affect the disease surveillance and control especially in pandemics such as influenza and COVID-19. In view of this, a portable, quantitative bioassay device will be valuable in regions with scarce medical resources and help relieve burden on local healthcare systems. Herein, we introduce the MagiCoil diagnostic device, an inexpensive, portable, quantitative, and rapid bioassay platform based on the magnetic particle spectrometer (MPS) technique. MPS detects the dynamic magnetic responses of magnetic nanoparticles (MNPs) and uses the harmonics from oscillating MNPs as metrics for sensitive and quantitative bioassays. This device does not require trained technicians to operate and employs a fully automatic, one-step, and wash-free assay with a user friendly smartphone interface. Using a streptavidin-biotin binding system as a model, we show that the detection limit of the current portable device for streptavidin is 64 nM (equal to 5.12 pmole). In addition, this MPS technique is very versatile and allows for the detection of different diseases just by changing the surface modifications on MNPs. Although MPS-based bioassays show high sensitivities as reported in many literatures, at the current stage, this portable device faces insufficient sensitivity and needs further improvements. It is foreseen that this kind of portable device can transform the multistep, laboratory-based bioassays to one-step field testing in nonclinical settings such as schools, homes, offices, etc.