A rapid RNA extraction-free lateral flow assay for molecular point-of-care detection of SARS-CoV-2 augmented by chemical probes

Unravelling the diagnostic methodologies for SARS-CoV-2; the Indispensable need for developing point-of-care testing

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-caused COVID-19 pandemic that continues to be a global menace and since its emergence in the late 2019, SARS-CoV-2 has been vigorously spreading throughout the globe putting the whole world into a multidimensional calamity. The suitable diagnosis strategies are on the front line of the battle against preventing the spread of infections. Since the clinical manifestation of COVID-19 is shared between various diseases, detection of the unique impacts of the pathogen on the host along with the diagnosis of the virus itself should be addressed. Employing the most suitable approaches to specifically, sensitively and effectively recognize the infected cases may be a real game changer in controlling the outbreak and the crisis management. In that matter, point-of-care assays (POC) appears to be the potential option, due to sensitivity, specificity, affordable, and availability. Here we brief the most recent findings about the virus, its variants, and the conventional methods that have been used for its detection, along with the POC strategies that have been applied to the virus diagnosis and the developing technologies which can accelerate the diagnosis procedure yet maintain its efficiency.

Colorimetric sensing for translational applications: from colorants to mechanisms

Colorimetric sensing offers instant reporting via visible signals. Versus labor-intensive and instrument-dependent detection methods, colorimetric sensors present advantages including short acquisition time, high throughput screening, low cost, portability, and a user-friendly approach. These advantages have driven substantial growth in colorimetric sensors, particularly in point-of-care (POC) diagnostics. Rapid progress in nanotechnology, materials science, microfluidics technology, biomarker discovery, digital technology, and signal pattern analysis has led to a variety of colorimetric reagents and detection mechanisms, which are fundamental to advance colorimetric sensing applications. This review first summarizes the basic components (e.g., color reagents, recognition interactions, and sampling procedures) in the design of a colorimetric sensing system. It then presents the rationale design and typical examples of POC devices, e.g., lateral flow devices, microfluidic paper-based analytical devices, and wearable sensing devices. Two highlighted colorimetric formats are discussed: combinational and activatable systems based on the sensor-array and lock-and-key mechanisms, respectively. Case discussions in colorimetric assays are organized by the analyte identities. Finally, the review presents challenges and perspectives for the design and development of colorimetric detection schemes as well as applications. The goal of this review is to provide a foundational resource for developing colorimetric systems and underscoring the colorants and mechanisms that facilitate the continuing evolution of POC sensors.

SERS-based microdevices for use as in vitro diagnostic biosensors

Advances in surface-enhanced Raman scattering (SERS) detection have helped to overcome the limitations of traditional in vitro diagnostic methods, such as fluorescence and chemiluminescence, owing to its high sensitivity and multiplex detection capability. However, for the implementation of SERS detection technology in disease diagnosis, a SERS-based assay platform capable of analyzing clinical samples is essential. Moreover, infectious diseases like COVID-19 require the development of point-of-care (POC) diagnostic technologies that can rapidly and accurately determine infection status. As an effective assay platform, SERS-based bioassays utilize SERS nanotags labeled with protein or DNA receptors on Au or Ag nanoparticles, serving as highly sensitive optical probes. Additionally, a microdevice is necessary as an interface between the target biomolecules and SERS nanotags. This review aims to introduce various microdevices developed for SERS detection, available for POC diagnostics, including LFA strips, microfluidic chips, and microarray chips. Furthermore, the article presents research findings reported in the last 20 years for the SERS-based bioassay of various diseases, such as cancer, cardiovascular diseases, and infectious diseases. Finally, the prospects of SERS bioassays are discussed concerning the integration of SERS-based microdevices and portable Raman readers into POC systems, along with the utilization of artificial intelligence technology.

Optical lateral flow assays in early diagnosis of SARS-CoV-2 infection

So far, the 2019 novel coronavirus (COVID-19) is spreading widely worldwide. The early diagnosis of infection by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is essential to provide timely treatment and prevent its further spread. Lateral flow assays (LFAs) have the advantages of rapid detection, simple operation, low cost, ease of mass production, and no need for special devices and professional operators, which make them suitable for self-testing at home. This review focuses on the early diagnosis of SARS-CoV-2 infection based on optical LFAs including colorimetric, fluorescent (FL), chemiluminescent (CL), and surface-enhanced Raman scattering (SERS) LFAs for the detection of SARS-CoV-2 antigens and nucleic acids. The types of recognition components, detection modes used for antigen detection, labels employed in different optical LFAs, and strategies to improve the detection sensitivity of LFAs were reviewed. Meanwhile, LFAs coupled with different nucleic acid amplification techniques and CRISPR-Cas systems for the detection of SARS-CoV-2 nucleic acids were summarized. We hope this review provides research mentalities for developing highly sensitive LFAs that can be used in home self-testing for the early diagnosis of SARS-CoV-2 infection.

Rapid and Sensitive Detection of Verticillium dahliae from Soil Using LAMP-CRISPR/Cas12a Technology

Cotton Verticillium wilt is mainly caused by the fungus Verticillium dahliae, which threatens the production of cotton. Its pathogen can survive in the soil for several years in the form of microsclerotia, making it a destructive soil-borne disease. The accurate, sensitive, and rapid detection of V. dahliae from complex soil samples is of great significance for the early warning and management of cotton Verticillium wilt. In this study, we combined the loop-mediated isothermal amplification (LAMP) with CRISPR/Cas12a technology to develop an accurate, sensitive, and rapid detection method for V. dahliae. Initially, LAMP primers and CRISPR RNA (crRNA) were designed based on a specific DNA sequence of V. dahliae, which was validated using several closely related Verticillium spp. The lower detection limit of the LAMP-CRISPR/Cas12a combined with the fluorescent visualization detection system is approximately ~10 fg/μL genomic DNA per reaction. When combined with crude DNA-extraction methods, it is possible to detect as few as two microsclerotia per gram of soil, with the total detection process taking less than 90 min. Furthermore, to improve the method's user and field friendliness, the field detection results were visualized using lateral flow strips (LFS). The LAMP-CRISPR/Cas12a-LFS system has a lower detection limit of ~1 fg/μL genomic DNA of the V. dahliae, and when combined with the field crude DNA-extraction method, it can detect as few as six microsclerotia per gram of soil, with the total detection process taking less than 2 h. In summary, this study expands the application of LAMP-CRISPR/Cas12a nucleic acid detection in V. dahliae and will contribute to the development of field-deployable diagnostic productions.

Molecular Interactions Leading to Advancements in the Techniques for COVID-19 Detection: A Review

Since 2019 the world has been in a combat with the highly contagious disease COVID-19 which is caused by the rapid transmission of the SARS-CoV-2 virus (severe acute respiratory syndrome coronavirus 2). Detection of this disease in an early stage helps to control its spread and management. To combat this epidemic with one-time effective medication, improved quick analytical procedures must be developed and validated. The requirement for accurate and precise analytical methods for the diagnosis of the virus and antibodies in infected patients has been a matter of concern. The global impact of this virus has motivated scientists and researchers to investigate and develop various analytical diagnostic techniques. This review includes the study of standard methods which are reliable and accredited for the analytical recognition of the said virus. For early detection of SARS-CoV-2 RNA, RT-PCR (Real-time reverse transcriptase-polymerase chain reaction) is an accurate method among other methods and, thus, considered as the "gold standard" technique. Here, we outline the most extensively used analytical methods for diagnosing COVID-19, along with a brief description of each technique and its analytical aspects/perspective.

Development of a self-contained microfluidic chip and an internet-of-things-based point-of-care device for automated identification of respiratory viruses

The COVID-19 pandemic greatly impacted the in vitro diagnostic market, leading to the development of new technologies such as point-of-care testing (POCT), multiplex testing, and digital health platforms. In this study, we present a self-contained microfluidic chip integrated with an internet-of-things (IoT)-based point-of-care (POC) device for rapid and sensitive diagnosis of respiratory viruses. Our platform enables sample-to-answer diagnostics within 70 min by automating RNA extraction, reverse transcription-loop-mediated isothermal amplification (RT-LAMP), and fluorescence detection. The microfluidic chip is designed to store all the necessary reagents for the entire diagnostic assay, including a lysis buffer, a washing buffer, an elution buffer, and a lyophilized RT-LAMP cocktail. It can perform nucleic acid extraction, aliquoting, and gene amplification in multiple reaction chambers without cross-contamination. The IoT-based POC device consists of a Raspberry Pi 4 for device control and data processing, a CMOS sensor for measuring fluorescence signals, a resistive heater panel for temperature control, and solenoid valves for controlling the movement of on-chip reagent solutions. The proposed device is portable and features a touchscreen for user control and result display. We evaluated the performance of the platform using 11 clinical respiratory virus samples, including 5 SARS-CoV-2 samples, 2 influenza A samples, and 4 influenza B samples. All tested clinical samples were accurately identified with high specificity and fidelity, demonstrating the ability to simultaneously detect multiple respiratory viruses. The combination of the integrated microfluidic chip with the POC device offers a simple, cost-effective, and scalable solution for rapid molecular diagnosis of respiratory viruses in resource-limited settings.

Hierarchical Nanobiosensors at the End of the SARS-CoV-2 Pandemic

Nanostructures have played a key role in the development of different techniques to attack severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Some applications include masks, vaccines, and biosensors. The latter are of great interest for detecting diseases since some of their features allowed us to find specific markers in secretion samples such as saliva, blood, and even tears. Herein, we highlight how hierarchical nanoparticles integrated into two or more low-dimensional materials present outstanding advantages that are attractive for photonic biosensing using their nanoscale functions. The potential of nanohybrids with their superlative mechanical characteristics together with their optical and optoelectronic properties is discussed. The progress in the scientific research focused on using nanoparticles for biosensing a variety of viruses has become a medical milestone in recent years, and has laid the groundwork for future disease treatments. This perspective analyzes the crucial information about the use of hierarchical nanostructures in biosensing for the prevention, treatment, and mitigation of SARS-CoV-2 effects.

Morphology Control of Self-Assembled Copper Coordination Polymers for Glucose Assays

Low-cost analytical assays enable accessible detection of clinically and environmentally important analytes; however, common enzyme-based assays suffer from high production and storage costs. Catalytically active synthetic materials serve as replacements for natural enzymes, but development of cost-effective, highly efficient synthetic strategies remains a challenge. Here, we utilized a facile synthesis for copper bipyridine coordination polymers (CuBpyCPs) and investigated structure-function relationships to achieve optimal catalytic properties for a glucose assay. We demonstrated the manipulation of CuBpyCP morphology, resulting in nanoscale petal-like structures and microscale high-index faceted structures, and identified three pure crystal morphologies exhibiting a comparable catalytic activity (Km = 0.3-0.5 mM) to horseradish peroxidase.

Microfluidic-assisted integrated nucleic acid test strips for POCT

Numerous diseases have posed significant threats to public health, notably the global pandemic of COVID-19, resulting in widespread devastation due to its high infectivity and severity. The nucleic acid lateral flow assay (NALFA) addresses challenges of complexity, cost, and time associated with traditional assays, offering a reliable platform for rapid and precise nucleic acid target detection. NALFA is gaining prominence as a point-of-care testing (POCT) technique, thanks to its user-friendly operation and rapid results. Nevertheless, conventional NALFA relies on specialized technicians and involves labor-intensive steps like DNA extraction and PCR processes, impeding its efficiency. To overcome these limitations, integrating NALFA with microfluidic technology, widely employed in rapid field detection, holds promise. This review comprehensively outlines prevailing strategies for integrating NALFA, encompassing both research initiatives and commercial applications. Addressing the bottleneck of nucleic acid amplification as a rate-limiting step, the review delves into progress in amplification-free NALFA and highlights prevalent signal amplification techniques. Ultimately, the review outlines the future prospect of integrated NALFA development, capturing the technology's evolution and providing valuable insights for academic and commercial endeavors.

Rapid assays of SARS-CoV-2 virus and noble biosensors by nanomaterials

The COVID-19 outbreak caused by SARS-CoV-2 in late 2019 has spread rapidly across the world to form a global epidemic of respiratory infectious diseases. Increased investigations on diagnostic tools are currently implemented to assist rapid identification of the virus because mass and rapid diagnosis might be the best way to prevent the outbreak of the virus. This critical review discusses the detection principles, fabrication techniques, and applications on the rapid detection of SARS-CoV-2 with three categories: rapid nuclear acid augmentation test, rapid immunoassay test and biosensors. Special efforts were put on enhancement of nanomaterials on biosensors for rapid, sensitive, and low-cost diagnostics of SARS-CoV-2 virus. Future developments are suggested regarding potential candidates in hospitals, clinics and laboratories for control and prevention of large-scale epidemic.

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

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

Mobile Point-of-Care Device Using Molecularly Imprinted Polymer-Based Chemosensors Targeting Interleukin-1β Biomarker

Molecularly imprinted polymers (MIPs) have garnered significant attention as a promising material for engineering specific biological receptors with superior chemical complementarity to target molecules. In this study, we present an electrochemical biosensing platform incorporating MIP films for the selective detection of the interleukin-1β (IL-1β) biomarker, particularly suitable for mobile point-of-care testing (POCT) applications. The IL-1β-imprinted biosensors were composed of poly(eriochrome black T (EBT)), including an interlayer of poly(3,4-ethylene dioxythiophene) and a 4-aminothiophenol monolayer, which were electrochemically polymerized simultaneously with template proteins (i.e., IL-1β) on custom flexible screen-printed carbon electrodes (SPCEs). The architecture of the MIP films was designed to enhance the sensor sensitivity and signal stability. This approach involved a straightforward sequential-electropolymerization process and extraction for leaving behind cavities (i.e., rebinding sites), resulting in the efficient production of MIP-based biosensors capable of molecular recognition for selective IL-1β detection. The electrochemical behaviors were comprehensively investigated using cyclic voltammograms and electrochemical impedance spectroscopy responses to assess the imprinting effect on the MIP films formed on the SPCEs. In line with the current trend in in vitro diagnostic medical devices, our simple and effective MIP-based analytical system integrated with mobile POCT devices offers a promising route to the rapid detection of biomarkers, with particular potential for periodontitis screening.

Highly-Specific Single-Stranded Oligonucleotides and Functional Nanoprobes for Clinical Determination of Chlamydia Trachomatis and Neisseria Gonorrhoeae Infections

Early detection of Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) is the key to controlling the spread of these bacterial infections. An important step in developing biosensors involves identifying reliable sensing probes against specific genetic targets for CT and NG. Here, the authors have designed single-stranded oligonucleotides (ssDNAs) targeting mutually conserved genetic regions of cryptic plasmid and chromosomal DNA of both CT and NG. The 5'- and 3'- ends of these ssDNAs are differentially functionalized with thiol groups and coupled with gold nanoparticles (AuNP) to develop absorbance-based assay. The AuNPs agglomerate selectively in the presence of its target DNA sequence and demonstrate a change in their surface plasmon resonance. The optimized assay is then used to detect both CT and NG DNA extracted from 60 anonymized clinical samples with a clinical sensitivity of ∼100%. The limit of detection of the assays are found to be 7 and 5 copies/µL for CT and NG respectively. Furthermore, it can successfully detect the DNA levels of these two bacteria without the need for DNA extraction and via a lateral flow-based platform. These assays thus hold the potential to be employed in clinics for rapid and efficient monitoring of sexually transmitted infections.

Simple and Multiplexed Detection of Nucleic Acid Targets Based on Fluorescent Ring Patterns and Deep Learning Analysis

Simple diagnostic tests for nucleic acid targets can provide great advantages for applications such as rapid pathogen detection. Here, we developed a membrane assay for multiplexed detection of nucleic acid targets based on the visualization of two-dimensional fluorescent ring patterns. A droplet of the assay solution is applied to a cellulose nitrate membrane, and upon radial chromatographic flow and evaporation of the solvent, fluorescent patterns appear under UV irradiation. The target nucleic acid is isothermally amplified and is immediately hybridized with fluorescent oligonucleotide probes in a one-pot reaction. We established the fluorescent ring assay integrated with isothermal amplification (iFluor-RFA = isothermal fluorescent ring-based radial flow assay), and feasibility was tested using nucleic acid targets of the receptor binding domain (RBD) and RNA-dependent RNA polymerase (RdRp) genes of SARS-CoV-2. We demonstrate that the iFluor-RFA method is capable of specific and sensitive detection in the subpicomole range, as well as multiplexed detection even in complex solutions. Furthermore, we applied deep learning analysis of the fluorescence images, showing that patterns could be classified as positive or negative and that quantitative amounts of the target could be predicted. The current technique, which is a membrane pattern-based nucleic acid assay combined with deep learning analysis, provides a novel approach in diagnostic platform development that can be versatilely applied for the rapid detection of infectious pathogens.

Development of practical techniques for simultaneous detection and distinction of current and emerging SARS-CoV-2 variants

Countless individuals have fallen victim to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and have generated antibodies, reducing the risk of secondary infection in the short term. However, with the emergence of mutated strains, the probability of subsequent infections remains high. Consequently, the demand for simple and accessible methods for distinguishing between different variants is soaring. Although monitoring viral gene sequencing is an effective approach for differentiating between various types of SARS-CoV-2 variants, it may not be easily accessible to the general public. In this article, we provide an overview of the reported techniques that use combined approaches and adaptable testing methods that use editable recognition receptors for simultaneous detection and distinction of current and emerging SARS-CoV-2 variants. These techniques employ straightforward detection strategies, including tests capable of simultaneously identifying and differentiating between different variants. Furthermore, we recommend advancing the development of uncomplicated protocols for distinguishing between current and emerging variants. Additionally, we propose further development of facile protocols for the differentiation of existing and emerging variants.

PCR-Free Innovative Strategies for SARS-CoV-2 Detection

The pandemic outbreak caused by SARS-CoV-2 coronavirus brought a crucial issue in public health causing up to now more than 600 million infected people and 6.5 million deaths. Conventional diagnostic methods are based on quantitative reverse transcription polymerase chain reaction (RT-qPCR assay) and immuno-detection (ELISA assay). However, despite these techniques have the advantages of being standardized and consolidated, they keep some main limitations in terms of accuracy (immunoassays), time/cost consumption of analysis, the need for qualified personnel, and lab constrain (molecular assays). There is crucial the need to develop new diagnostic approaches for accurate, fast and portable viral detection and quantification. Among these, PCR-free biosensors represent the most appealing solution since they can allow molecular detection without the complexity of the PCR. This will enable the possibility to be integrated in portable and low-cost systems for massive and decentralized screening of SARS-CoV-2 in a point-of-care (PoC) format, pointing to achieve a performant identification and control of infection. In this review, the most recent approaches for the SARS-CoV-2 PCR-free detection are reported, describing both the instrumental and methodological features, and highlighting their suitability for a PoC application.

Updates on the Biofunctionalization of Gold Nanoparticles for the Rapid and Sensitive Multiplatform Diagnosis of SARS-CoV-2 Virus and Its Proteins: From Computational Models to Validation in Human Samples

Since the outbreak of the pandemic respiratory virus SARS-CoV-2 (COVID-19), academic communities and governments/private companies have used several detection techniques based on gold nanoparticles (AuNPs). In this emergency context, colloidal AuNPs are highly valuable easy-to-synthesize biocompatible materials that can be used for different functionalization strategies and rapid viral immunodiagnosis. In this review, the latest multidisciplinary developments in the bioconjugation of AuNPs for the detection of SARS-CoV-2 virus and its proteins in (spiked) real samples are discussed for the first time, with reference to the optimal parameters provided by three approaches: one theoretical, via computational prediction, and two experimental, using dry and wet chemistry based on single/multistep protocols. Overall, to achieve high specificity and low detection limits for the target viral biomolecules, optimal running buffers for bioreagent dilutions and nanostructure washes should be validated before conducting optical, electrochemical, and acoustic biosensing investigations. Indeed, there is plenty of room for improvement in using gold nanomaterials as stable platforms for ultrasensitive and simultaneous "in vitro" detection by the untrained public of the whole SARS-CoV-2 virus, its proteins, and specific developed IgA/IgM/IgG antibodies (Ab) in bodily fluids. Hence, the lateral flow assay (LFA) approach is a quick and judicious solution to combating the pandemic. In this context, the author classifies LFAs according to four generations to guide readers in the future development of multifunctional biosensing platforms. Undoubtedly, the LFA kit market will continue to improve, adapting researchers' multidetection platforms for smartphones with easy-to-analyze results, and establishing user-friendly tools for more effective preventive and medical treatments.

Binding-Induced Folding of DNA Oligonucleotides Targeted to the Nucleocapsid Gene Enables Electrochemical Sensing of SARS-CoV-2

In the wake of the COVID-19 pandemic, millions of confirmed cases and deaths have been reported around the world. COVID-19 spread can be slowed and eventually stopped by a rapid test to diagnose positive cases of the disease on the spot. It is still important to test for COVID-19 quickly regardless of the availability of the vaccine. Using the binding-induced folding principle, we developed an electrochemical test for detecting SARS-CoV-2 with no RNA extraction or nucleic acid amplification. The test showed high sensitivity with a limit of detection of 2.5 copies/μL. An electrode mounted with a capture probe and a portable potentiostat are used to conduct the test. To target the N-gene of SARS-CoV-2, a highly specific oligo-capturing probe was used. Based on the binding-induced "folding" principle, the sensor detects binding between the oligo and RNA. When the target is absent, the capture probe tends to form a hairpin as a secondary structure, retaining the redox reporter close to the surface. This can be seen as a large anodic and cathodic peak current. When the target RNA is present, the hairpin structure will open to hybridize with its complementary sequence, causing the redox reporter to pull away from the electrode. Consequently, the anodic/cathodic peak currents are reduced, indicating the presence of the SARS-CoV-2 genetic material. Validation of the test performance was performed using 122 COVID-19 clinical samples (55 positives and 67 negatives) and benchmarked to the gold standard reverse transcription-polymerase chain reaction (RT-PCR) test. As a result of our test, the accuracy, sensitivity, and specificity have been measured at 98.4%, 98.2%, and 98.5%, respectively.

One-step synthesis of triethanolamine-capped Pt nanoparticle for colorimetric and electrochemiluminescent immunoassay of SARS-CoV spike proteins

Platinum nanoparticles (PtNPs) have been attracted worldwide attention due to their versatile application potentials, especially in the catalyst and sensing fields. Herein, a facile synthetic method of triethanolamine (TEOA)-capped PtNPs (TEOA@PtNP) for electrochemiluminescent (ECL) and colorimetric immunoassay of SARS-CoV spike proteins (SARS-CoV S-protein, a target detection model) is developed. Monodisperse PtNPs with an average diameter of 2.2 nm are prepared by a one-step hydrothermal synthesis method using TEOA as a green reductant and stabilizer. TEOA@PtNPs can be used as a nanocarrier to combine with antigen by the high-affinity antibody, which leads to a remarkable inhibition of electron transfer efficiency and mass transfer processes. On the basis of its peroxidase-like activity and easy-biolabeling property, the TEOA@PtNP can be used to establish a colorimetric immunosensor of SARS-CoV S-protein thought catalyzing the reaction of H₂O₂ and 3,3',5,5'-tetramethylbenzidine (TMB). Especially, the Ru(bpy)₃ ²⁺ ECL reaction is well-achieved with the TEOA@PtNPs due to their great conductivity and loading abundant TEOA co-reactants, resulting in an enhancing ECL signal in immunoassay of SARS-CoV S-protein. As a consequence, two proposed methods could achieve sensitive detection of SARS-CoV S-protein in wide ranges, the colorimetric and ECL detection limits were as low as 8.9 fg /mL and 4.2 fg /mL (S/N = 3), respectively. We believe that the proposed colorimetric and ECL immunosesors with high sensitivity, good reproducibility, and good stability will be a promising candidate for a broad spectrum of applications.

Affordable on-site COVID-19 test using non-powered preconcentrator

A simple, affordable point of care test (POCT) is necessary for on-site detection of coronavirus disease 2019 (COVID-19). The lateral flow assay (LFA) has great potential for use in POCT mainly because of factors such as low time consumption, low cost, and ease of use. However, it lacks sensitivity and limits of detection (LOD), which are essential for early diagnostics. In this study, we proposed a non-powered preconcentrator (NPP) based on nanoelectrokinetics for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Antigen (Ag) lateral flow assay. The non-powered preconcentrator is composed of glass fiber-based composite paper and ion permselective material, and it can be simply operated by force balancing gravitational, capillary, and depletion-induced forces. The proposed approach helps enrich the SARS-CoV-2 viral nucleocapsid (N) proteins based on a 10-min operation, and it improved the LOD by up to 10-fold. The corresponding virus enrichment, which was evaluated using the reverse-transcriptase polymerase chain reaction (RT-PCR), revealed an improvement in ΔCt values > 3. We successfully demonstrated the enhancement of the NPP-assisted LFA, we extended to applying it to clinical samples. Further, we demonstrated an affordable, easy-to-implement form of LFA by simply designing NPP directly on the LFA buffer tube.

Potential of vibrational spectroscopy coupled with machine learning as a non-invasive diagnostic method for COVID-19

BACKGROUND AND OBJECTIVE

Efforts to alleviate the ongoing coronavirus disease 2019 (COVID-19) crisis showed that rapid, sensitive, and large-scale screening is critical for controlling the current infection and that of ongoing pandemics.

METHODS

Here, we explored the potential of vibrational spectroscopy coupled with machine learning to screen COVID-19 patients in its initial stage. Herein presented is a hybrid classification model called grey wolf optimized support vector machine (GWO-SVM). The proposed model was tested and comprehensively compared with other machine learning models via vibrational spectroscopic fingerprinting including saliva FTIR spectra dataset and serum Raman scattering spectra dataset.

RESULTS

For the unknown vibrational spectra, the presented GWO-SVM model provided an accuracy, specificity and F1_score value of 0.9825, 0.9714 and 0.9778 for saliva FTIR spectra dataset, respectively, while an overall accuracy, specificity and F1_score value of 0.9085, 0.9552 and 0.9036 for serum Raman scattering spectra dataset, respectively, which showed superiority than those of state-of-the-art models, thereby suggesting the suitability of the GWO-SVM model to be adopted in a clinical setting for initial screening of COVID-19 patients.

CONCLUSIONS

Prospectively, the presented vibrational spectroscopy based GWO-SVM model can facilitate in screening of COVID-19 patients and alleviate the medical service burden. Therefore, herein proof-of-concept results showed the chance of vibrational spectroscopy coupled with GWO-SVM model to help COVID-19 diagnosis and have the potential be further used for early screening of other infectious diseases.

Sandwich mode lateral flow assay for point-of-care detecting SARS-CoV-2

The global corona virus disease 2019 (COVID-19) has been announced a pandemic outbreak, and has threatened human life and health seriously. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as its causative pathogen, is widely detected in the screening of COVID-19 patients, infected people and contaminated substances. Lateral flow assay (LFA) is a popular point-of-care detection method, possesses advantages of quick response, simple operation mode, portable device, and low cost. Based on the above advantages, LFA has been widely developed for detecting SARS-CoV-2. In this review, we summarized the articles about the sandwich mode LFA detecting SARS-CoV-2, classified according to the target detection objects indicating genes, nucleocapsid protein, spike protein, and specific antibodies of SARS-CoV-2. In each part, LFA is further classified and summarized according to different signal detection types. Additionally, the properties of the targets were introduced to clarify their detection significance. The review is expected to provide a helpful guide for LFA sensitization and marker selection of SARS-CoV-2.

Achieving broad availability of SARS-CoV-2 detections via smartphone-based analysis

With the development of COVID-19, widely available tests are in great demand. Naked-eye SARS-CoV-2 test kits have recently been developed as home tests, but their sensitivity and accuracy are sometimes limited. Smartphones can convert various signals into digital information, potentially improving the sensitivity and accuracy of these home tests. Herein, we summarize smartphone-based detections for SARS-CoV-2. Optical detections of non-nucleic acids using various sensors and portable imaging systems, as well as nucleic acid analyses based on LAMP, CRISP, CATCH, and biosensors are discussed. Furthermore, different electrochemical detections were compared. We show results obtained using relatively complex equipment, complicated programming procedures, or custom smartphone apps, and describe methods for obtaining information with only simple setups and free software on smartphones. Then, the combined costs of typical smartphone-based detections are evaluated. Finally, the prospect of improving smartphone-based strategies to achieve broad availability of SARS-CoV-2 detection is proposed.

Advances in RT-LAMP for COVID-19 testing and diagnosis

INTRODUCTION

The SARS-CoV-2 pandemic, and the subsequent limitations on standard diagnostics, has vastly expanded the user base of Reverse Transcription Loop-mediated isothermal Amplification (RT-LAMP) in fundamental research and development. RT-LAMP has also penetrated commercial markets, with emergency use authorizations for clinical diagnosis.

AREAS COVERED

This review discusses the role of RT-LAMP within the context of other technologies like RT-qPCR and rapid antigen tests, progress in sample preparation strategies to enable simplified workflow for RT-LAMP directly from clinical specimens, new challenges with primer and assay design for the evolving pandemic, prominent detection modalities including colorimetric and CRISPR-mediated methods, and translational research and commercial development of RT-LAMP for clinical applications.

EXPERT OPINION

RT-LAMP occupies a middle ground between RT-qPCR and rapid antigen tests. The simplicity approaches that of rapid antigen tests, making it suitable for point-of-care use, but the sensitivity nears that of RT-qPCR. RT-LAMP still lags RT-qPCR in fundamental understanding of the mechanism, and the interplay between sample preparation and assay performance. Industry is now beginning to address issues around scalability and usability, which could finally enable LAMP and RT-LAMP to find future widespread application as a diagnostic for other conditions, including other pathogens with pandemic potential.

Role of Wearable Sensing Technology to Manage Long COVID

Long COVID consequences have changed the perception towards disease management, and it is moving towards personal healthcare monitoring. In this regard, wearable devices have revolutionized the personal healthcare sector to track and monitor physiological parameters of the human body continuously. This would be largely beneficial for early detection (asymptomatic and pre-symptomatic cases of COVID-19), live patient conditions, and long COVID monitoring (COVID recovered patients and healthy individuals) for better COVID-19 management. There are multitude of wearable devices that can observe various human body parameters for remotely monitoring patients and self-monitoring mode for individuals. Smart watches, smart tattoos, rings, smart facemasks, nano-patches, etc., have emerged as the monitoring devices for key physiological parameters, such as body temperature, respiration rate, heart rate, oxygen level, etc. This review includes long COVID challenges for frequent monitoring of biometrics and its possible solution with wearable device technologies for diagnosis and post-therapy of diseases.

Amplification Free Detection of SARS-CoV-2 Using Multi-Valent Binding

We present the development of electrochemical impedance spectroscopy (EIS)-based biosensors for sensitive detection of SARS-CoV-2 RNA using multi-valent binding. By increasing the number of probe-target binding events per target molecule, multi-valent binding is a viable strategy for improving the biosensor performance. As EIS can provide sensitive and label-free measurements of nucleic acid targets during probe-target hybridization, we used multi-valent binding to build EIS biosensors for targeting SARS-CoV-2 RNA. For developing the biosensor, we explored two different approaches including probe combinations that individually bind in a single-valent fashion and the probes that bind in a multi-valent manner on their own. While we found excellent biosensor performance using probe combinations, we also discovered unexpected signal suppression. We explained the signal suppression theoretically using inter- and intra-probe hybridizations which confirmed our experimental findings. With our best probe combination, we achieved a LOD of 182 copies/μL (303 aM) of SARS-CoV-2 RNA and used these for successful evaluation of patient samples for COVID-19 diagnostics. We were also able to show the concept of multi-valent binding with shorter probes in the second approach. Here, a 13-nt-long probe has shown the best performance during SARS-CoV-2 RNA binding. Therefore, multi-valent binding approaches using EIS have high utility for direct detection of nucleic acid targets and for point-of-care diagnostics.

Current trends in COVID-19 diagnosis and its new variants in physiological fluids: Surface antigens, antibodies, nucleic acids, and RNA sequencing

Rapid, highly sensitive, and accurate virus circulation monitoring techniques are critical to limit the spread of the virus and reduce the social and economic burden. Therefore, point-of-use diagnostic devices have played a critical role in addressing the outbreak of COVID-19 (SARS-CoV-2) viruses. This review provides a comprehensive overview of the current techniques developed for the detection of SARS-CoV-2 in various body fluids (e.g., blood, urine, feces, saliva, tears, and semen) and considers the mutations (i.e., Alpha, Beta, Gamma, Delta, Omicron). We classify and comprehensively discuss the detection methods depending on the biomarker measured (i.e., surface antigen, antibody, and nucleic acid) and the measurement techniques such as lateral flow immunoassay (LFIA), enzyme-linked immunosorbent assay (ELISA), reverse transcriptase-polymerase chain reaction (RT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP), microarray analysis, clustered regularly interspaced short palindromic repeats (CRISPR) and biosensors. Finally, we addressed the challenges of rapidly identifying emerging variants, detecting the virus in the early stages of infection, the detection sensitivity, selectivity, and specificity, and commented on how these challenges can be overcome in the future.

Rapid and Accurate On-Site Immunodiagnostics of Highly Contagious Severe Acute Respiratory Syndrome Coronavirus 2 Using Portable Surface-Enhanced Raman Scattering-Lateral Flow Assay Reader

In early 2022, the number of people infected with the highly contagious mutant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), called Omicron, was increasing worldwide. Therefore, several countries approved the lateral flow assay (LFA) strip as a diagnostic method for confirming SARS-CoV-2 instead of reverse transcription-polymerase chain reaction (RT-PCR), which takes a long time to generate the results. However, owing to the limitation of detection sensitivity, commercial LFA strips have high false-negative diagnosis rates for patients with low virus concentrations. Therefore, in this study, we developed a portable surface-enhanced Raman scattering (SERS)-LFA reader based on localized surface plasmon effects to solve the sensitivity problem of the commercial LFA strip. We tested 54 clinical samples using this portable SERS-LFA reader, which generated 49 positive and 5 negative results. Out of the 49 positive results, SERS-LFA classified only 2 as false negative, while the commercial LFA classified 21 as false negative. This confirmed that the false-negative rate had significantly improved compared to that of commercial LFA strips. We believe that the proposed SERS-LFA system can be utilized as a point-of-care diagnostic system to quickly and accurately determine a virus infection that could spread significantly within a short period.

Emerging Multiplex Nucleic Acid Diagnostic Tests for Combating COVID-19

The COVID-19 pandemic caused by SARS-CoV-2 has drawn attention to the need for fast and accurate diagnostic testing. Concerns from emerging SARS-CoV-2 variants and other circulating respiratory viral pathogens further underscore the importance of expanding diagnostic testing to multiplex detection, as single-plex diagnostic testing may fail to detect emerging variants and other viruses, while sequencing can be too slow and too expensive as a diagnostic tool. As a result, there have been significant advances in multiplex nucleic-acid-based virus diagnostic testing, creating a need for a timely review. This review first introduces frequent nucleic acid targets for multiplex virus diagnostic tests, then proceeds to a comprehensive and up-to-date overview of multiplex assays that incorporate various detection reactions and readout modalities. The performances, advantages, and disadvantages of these assays are discussed, followed by highlights of platforms that are amenable for point-of-care use. Finally, this review points out the remaining technical challenges and shares perspectives on future research and development. By examining the state of the art and synthesizing existing development in multiplex nucleic acid diagnostic tests, this review can provide a useful resource for facilitating future research and ultimately combating COVID-19.

A Molecular Lateral Flow Assay for SARS-CoV-2 Quantitative Detection

Since the onset of the SARS-CoV-2 pandemic, several COVID-19 detection methods, both commercially available and in the lab, have been developed using different biomolecules as analytes and different detection and sampling methods with high analytical performance. Developing novel COVID-19 detection assays is an exciting research field, as rapid accurate diagnosis is a valuable tool to control the current pandemic, and also because the acquired knowledge can be deployed for facing future infectious outbreaks. We here developed a novel gold-nanoparticle-based nucleic acid lateral flow assay for the rapid, visual, and quantitative detection of SARS-CoV-2. Our method was based on the use of a DNA internal standard (competitor) for quantification and involved RT-PCR, the hybridization of biotinylated PCR products to specific oligonucleotide probes, and detection with a dual lateral flow assay using gold nanoparticles conjugated to an anti-biotin antibody as reporters. The developed test allowed for rapid detection by the naked eye and the simultaneous quantification of SARS-CoV-2 in nasopharyngeal swabs with high specificity, detectability, and repeatability. This novel molecular strip test for COVID-19 detection represents a simple, cost-effective, and accurate rapid test that is very promising to be used as a future diagnostic tool.

Diagnostic accuracy of clinically applied nanoparticle-based biosensors at detecting SARS-CoV-2 RNA and surface proteins in pharyngeal swabs compared to RT-PCR as a reference test

INTRODUCTION

Nanoparticle-based biosensors (NPBs) are point-of-care diagnostic platforms that can be used for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with high accuracy.

AREAS COVERED

EBSCOhost Web, Embase, ProQuest, PubMed/MEDLINE, Scopus, Web of Science, and WHO Global Literature on Coronavirus Disease 2019 (COVID-19) were searched for relevant records published from 1 November 2019 to 30 April 2022. Records reporting original data on the accuracy of clinically applied nanoparticle-based biosensors at detecting SARS-CoV-2 RNA and surface proteins from pharyngeal swab specimens were considered. Findings were reported based on the PRISMA 2020 statement. The QUADAS-2 tool was used for assessment of quality and risk of bias among the included studies.

EXPERT OPINION

A total of 50 relevant records were identified, of which 13 were included. The included studies explored the diagnostic performance of 13 clinically applied distinct nanoparticle-based biosensors in a total of 789 pharyngeal swabs collected from 376 COVID-19 patients and 413 otherwise healthy individuals. The mean sensitivity, specificity, and accuracy were 97.07%, 94.43%, and 96.91%, respectively, in comparison to RT-qPCR as the reference test. Considering their ease-of-operation, portability, low-cost manufacturing, NPBs could be considered suitable candidate diagnostic platforms for substituting RT-qPCR.

Diagnostic Approaches For COVID-19: Lessons Learned and the Path Forward

Coronavirus disease 2019 (COVID-19) is a transmitted respiratory disease caused by the infection of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although humankind has experienced several outbreaks of infectious diseases, the COVID-19 pandemic has the highest rate of infection and has had high levels of social and economic repercussions. The current COVID-19 pandemic has highlighted the limitations of existing virological tests, which have failed to be adopted at a rate to properly slow the rapid spread of SARS-CoV-2. Pandemic preparedness has developed as a focus of many governments around the world in the event of a future outbreak. Despite the largely widespread availability of vaccines, the importance of testing has not diminished to monitor the evolution of the virus and the resulting stages of the pandemic. Therefore, developing diagnostic technology that serves as a line of defense has become imperative. In particular, that test should satisfy three criteria to be widely adopted: simplicity, economic feasibility, and accessibility. At the heart of it all, it must enable early diagnosis in the course of infection to reduce spread. However, diagnostic manufacturers need guidance on the optimal characteristics of a virological test to ensure pandemic preparedness and to aid in the effective treatment of viral infections. Nanomaterials are a decisive element in developing COVID-19 diagnostic kits as well as a key contributor to enhance the performance of existing tests. Our objective is to develop a profile of the criteria that should be available in a platform as the target product. In this work, virus detection tests were evaluated from the perspective of the COVID-19 pandemic, and then we generalized the requirements to develop a target product profile for a platform for virus detection.

Flexible Terahertz Metamaterial Biosensor for Ultra-Sensitive Detection of Hepatitis B Viral DNA Based on the Metal-Enhanced Sandwich Assay

The high sensitivity and specificity of terahertz (THz) biosensing are both promising and challenging in DNA sample detection. This study produced and refined a flexible THz MM biosensor for ultrasensitive detection of HBV in clinical serum samples based on a gold magnetic nanoparticle-mediated rolling circle amplification (GMNPs@RCA) sandwich assay under isothermal conditions. Typically, solid-phase RCA reactions mediated by circular padlock probes (PLPs) are triggered under isothermal conditions in the presence of HBV DNA, resulting in long single-stranded DNA (ssDNA) with high fidelity and specificity. Then, the resultant ssDNA was conjugated with detection probes (DPs) immobilized on gold nanoparticles (DP@AuNPs) to form GMNPs-RCA-AuNPs sandwich complexes. The HBV DNA concentrations were quantified by introducing GMNPs-RCA-AuNPs complexes into the metasurface of a flexible THz metamaterial-based biosensor chip and resulting in a red shift of the resonance peak of the THz metamaterials. This biosensor can lead to highly specific and sensitive detection with one-base mismatch discrimination and a limit of detection (LOD) down to 1.27E + 02 IU/ml of HBV DNA from clinical serum samples. The HBV DNA concentration was linearly correlated with the frequency shift of the THz metamaterials within the range of 1.27E + 02∼1.27E + 07 IU/ml, illustrating the applicability and accuracy of our assay in real clinical samples. This strategy constitutes a promising THz sensing method to identify virus DNA. In the future, it is hoped it can assist with pathogen identification and clinical diagnosis.

A Machine Learning Framework for Detecting COVID-19 Infection Using Surface-Enhanced Raman Scattering

In this study, we explored machine learning approaches for predictive diagnosis using surface-enhanced Raman scattering (SERS), applied to the detection of COVID-19 infection in biological samples. To do this, we utilized SERS data collected from 20 patients at the University of Maryland Baltimore School of Medicine. As a preprocessing step, the positive-negative labels are obtained using Polymerase Chain Reaction (PCR) testing. First, we compared the performance of linear and nonlinear dimensionality techniques for projecting the high-dimensional Raman spectra to a low-dimensional space where a smaller number of variables defines each sample. The appropriate number of reduced features used was obtained by comparing the mean accuracy from a 10-fold cross-validation. Finally, we employed Gaussian process (GP) classification, a probabilistic machine learning approach, to correctly predict the occurrence of a negative or positive sample as a function of the low-dimensional space variables. As opposed to providing rigid class labels, the GP classifier provides a probability (ranging from zero to one) that a given sample is positive or negative. In practice, the proposed framework can be used to provide high-throughput rapid testing, and a follow-up PCR can be used for confirmation in cases where the model's uncertainty is unacceptably high.

Advancements in Testing Strategies for COVID-19

The SARS-CoV-2 coronavirus, also known as the disease-causing agent for COVID-19, is a virulent pathogen that may infect people and certain animals. The global spread of COVID-19 and its emerging variation necessitates the development of rapid, reliable, simple, and low-cost diagnostic tools. Many methodologies and devices have been developed for the highly sensitive, selective, cost-effective, and rapid diagnosis of COVID-19. This review organizes the diagnosis platforms into four groups: imaging, molecular-based detection, serological testing, and biosensors. Each platform's principle, advancement, utilization, and challenges for monitoring SARS-CoV-2 are discussed in detail. In addition, an overview of the impact of variants on detection, commercially available kits, and readout signal analysis has been presented. This review will expand our understanding of developing advanced diagnostic approaches to evolve into susceptible, precise, and reproducible technologies to combat any future outbreak.

Nanoelectrokinetic-assisted lateral flow assay for COVID-19 antibody test

A lateral flow assay (LFA) platform is a powerful tool for point-of-care testing (POCT), especially for self-testing. Although the LFA platform provides a simple and disposable tool for Coronavirus disease of 2019 (COVID-19) antigen (Ag) and antibody (Ab) screening tests, the lower sensitivity for low virus titers has been a bottleneck for practical applications. Herein, we report the combination of a microfluidic paper-based nanoelectrokinetic (NEK) preconcentrator and an LFA platform for enhancing the sensitivity and limit of detection (LOD). Biomarkers were electrokinetically preconcentrated onto a specific layer using the NEK preconcentrator, which was then coupled with LFA diagnostic devices for enhanced performance. Using this nanoelectrokinetic-assisted LFA (NEK-LFA) platform for self-testing, the severe acute respiratory syndrome coronavirus 2 Immunoglobulin G (SARS-CoV-2 IgG) sample was preconcentrated from serum samples. After preconcentration, the LOD of the LFA was enhanced by 32-fold, with an increase in analytical sensitivity (16.4%), which may offer a new opportunity for POCT and self-testing, especially in the COVID-19 pandemic and endemic global context.

Recent Progress on Rapid Lateral Flow Assay-Based Early Diagnosis of COVID-19

The outbreak of the coronavirus disease 2019 (COVID-19) has resulted in enormous losses worldwide. Through effective control measures and vaccination, prevention and curbing have proven significantly effective; however, the disease has still not been eliminated. Therefore, it is necessary to develop a simple, convenient, and rapid detection strategy for controlling disease recurrence and transmission. Taking advantage of their low-cost and simple operation, point-of-care test (POCT) kits for COVID-19 based on the lateral flow assay (LFA) chemistry have become one of the most convenient and widely used screening tools for pathogens in hospitals and at home. In this review, we introduce essential features of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, compare existing detection methods, and focus on the principles, merits and limitations of the LFAs based on viral nucleic acids, antigens, and corresponding antibodies. A systematic comparison was realized through summarization and analyses, providing a comprehensive demonstration of the LFA technology and insights into preventing and curbing the COVID-19 pandemic.

N-gene-complementary antisense-oligonucleotide directed molecular aggregation of dual-colour carbon dots, leading to efficient fluorometric sensing of SARS-COV-2 RNA

The early stages of the COVID-19 pandemic punctuated the need for rapid, mass testing for early detection of viral infection. Carbon dots are easily synthesized, cost-effective fluorescent nanoparticles whose surface functionalities enable facile conjugation with biorecognition elements suitable for  molecular detection of viral RNA. Herein, we report that a pair of complementary antisense oligonucleotide (ASO) sequences can lead to a highly specific molecular aggregation of dual colour carbon dots (CDs) in the presence of SARS-CoV-2 RNA. The nanoprobes used ASOs highly specific to the N-gene of SARS-COV-2. When the ASOs are conjugated to blue and yellow citric acid-derived CDs, the combination of the ASO-CD pairs facilitates aggregation-induced emission enhancement (AIEE) of the measured fluorescence after hybridization with SARS-CoV-2 RNA. We found the sensor capable of differentiating between MERS-CoV and SARS-CoV-2 samples and was found to have a limit of detection of 81 copies per μL. Additionally, we used dialysis to demonstrate that the change in emission upon aggregation is dependent on the compositional heterogeneity of the conjugated-carbon dot mixture.