A rapid water bath PCR combined with lateral flow assay for the simultaneous detection of SARS-CoV-2 and influenza B virus

Lateral flow assays: Progress and evolution of recent trends in point-of-care applications

Paper based point-of-care (PoC) detection platforms applying lateral flow assays (LFAs) have gained paramount approval in the diagnostic domain as well as in environmental applications owing to their ease of utility, low cost, and rapid signal readout. It has centralized the aspect of self-evaluation exhibiting promising potential in the last global pandemic era of Covid-19 implementing rapid management of public health in remote areas. In this perspective, the present review is focused towards landscaping the current framework of LFAs along with integration of components and characteristics for improving the assay by pushing the detection limits. The review highlights the synergistic aspects of assay designing, sample enrichment strategies, novel nanomaterials-based signal transducers, and high-end analytical techniques that contribute significantly towards sensitivity and specificity enhancement. Various recent studies are discussed supporting the innovations in LFA systems that focus upon the accuracy and reliability of rapid PoC testing. The review also provides a comprehensive overview of all the possible difficulties in commercialization of LFAs subjecting its applicability to pathogen surveillance, water and food testing, disease diagnostics, as well as to agriculture and environmental issues.

Development of immunochromatographic and homogeneous assay based on quantum dot-functionalized polystyrene nanoprobes for the qualitative and quantitative screening of respiratory viruses

Accurately differentiating respiratory diseases caused by viruses is challenging because of the similarity in their early or clinical symptoms. Moreover, different infection sources require different treatments. However, the current diagnostic methods have limited differentiating efficiency and sensitivity. We developed a dual-system immunosensor with a bilayer fluorescent label as a signal amplifier for the on-site, sensitive, and accurate identification of multiple respiratory viruses (RVs). The nanomaterial, comprising a polystyrene (PS) nanosphere core encapsulated by two layers of CdSe@ZnS-COOH quantum dots (QDs), outperforms the conventional color and fluorescent labels in RV detection. The dual-system detection platform, comprising a PS@DQD-based lateral flow immunoassay (LFIA) and a PS@DQD-based homogeneous sensor, enables qualitative and quantitative screening of multiple respiratory viruses within 10 and 30 min, respectively, depending on the specific detection requirements for different application scenarios. This remarkable method provides 51.2 to 1000 times sensitivity improvement over commercial antigen detection kits and greater than 12.5 to 100 times improvement over QD-based immunosensors. Furthermore, we comprehensively evaluated the specificity, reproducibility, and stability of the integrated dual-system detection platform, demonstrating its reliability. Remarkably, the respiratory viral testing was validated using biological samples, thus illustrating its promise and convenience in the detection of respiratory viruses.

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.

A sensitive gold nanoflower-based lateral flow assay coupled with gold staining technique for the detection of SARS-CoV-2 antigen

An enhanced lateral flow assay (LFA) is presented for rapid and highly sensitive detection of acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antigens with gold nanoflowers (Au NFs) as signaling markers and gold enhancement to amplify the signal intensities. First, the effect of the morphology of gold nanomaterials on the sensitivity of LFA detection was investigated. The results showed that Au NFs prepared by the seed growth method showed a 5-fold higher detection sensitivity than gold nanoparticles (Au NPs) of the same particle size, which may benefit from the higher extinction coefficient and larger specific surface area of Au NFs. Under the optimized experimental conditions, the Au NFs-based LFA exhibited a detection limit (LOD) of 25 pg mL-1 for N protein using 135 nm Au NFs as the signaling probes. The signal was further amplified by using a gold enhancement strategy, and the LOD for the detection of N protein achieved was 5 pg mL-1. The established LFA also exhibited good repeatability and stability and showed applicability in the diagnosis of SARS-CoV-2 infection.

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.

A fully integrated duplex RT-LAMP device for the detection of viral infections

Respiratory viruses can cause epidemics or pandemics, which are worldwide outbreaks of disease. The severity of these events varies depending on the virus, its characteristics, along with environmental factors. The frequency of epidemics and pandemics caused by respiratory viruses is difficult to predict, but the potential severity of such events underlines the importance of continued monitoring, research, and preparation for emerging infectious diseases. To help improve pandemic preparedness, we created a fully integrated duplex reverse transcription loop-mediated isothermal amplification (RT-LAMP) device targeting two respiratory viruses, influenza A/X-31 virus and bovine coronavirus, as a replacement for SARS-CoV-2. This device can be adapted to any other respiratory virus. In this study, we showed and evaluated a prototype of a microfluidic system, and showed that duplex RT-LAMP can detect and distinguish between the two viruses, with LoDs of 2,000 copies/ml for bovine coronavirus and 200 copies/ml for influenza A/X-31 virus.

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.

Nanotechnology meets immunology towards a rapid diagnosis solution: the COVID-19 outbreak challenge

The current COVID-19 pandemic presents one of the greatest challenges in human history. There is a consensus that the rapid and accurate diagnosis of COVID-19 directly affects procedures to avoid dissemination, promote treatments, and favor the prognosis of infected patients. This interdisciplinary study aims at designing new synthetic peptides inspired by the SARS-CoV-2 spike protein (SARS-CoV-2S) to produce rapid detection tests relying on nanomaterial-based colorimetric properties. Hence, in silico analyses of SARS-CoV-2S were performed using advanced bioinformatic simulation tools and algorithms. Five novel peptide sequences were proposed, and three were selected (P2, J4, and J5) based on their prospective reactivity against positive serum from naturally COVID-19-infected humans. Next, hyperimmune sera against the selected peptides were produced in rabbits. Concurrently, gold nanoparticles (AuNP) were synthesized using a green aqueous method under mild conditions through in situ reduction by trisodium citrate salt. They were extensively characterized by their morphological, physicochemical, and optical properties. The AuNPs demonstrated colloidal chemical stability in aqueous media, with an average size of approximately 29 nm (metallic core), and zeta potential before and after bioconjugation of -43 mV and -31 mV, respectively. Moreover, they presented an intense reddish-bluish color due to the surface plasmon resonance (SPR) effect, with maxima at λ = 525 nm and 536 nm, before and after bioconjugation, respectively, evidencing their applicability as colorimetric biomarkers for antigen-antibody immunoassay detection. To develop a rapid COVID-19 diagnosis test using lateral flow assay (LFA), semi-purified anti-SARS-CoV-2S sera against the three selected peptides were bioconjugated to the AuNPs as the highly optically sensitive agents using a considerably low antibody concentration (0.2 mg mL-1). All tested peptide sequences (P2, J4, and J5) induced antibodies capable of identifying the presence of SARS-CoV-2 virus inactivate suspensions (1 : 10, 1 : 100, or 1 : 1000 dilutions). For LFA positive test control, an anti-rabbit antibody was used. In summary, this research comprises several contributions and advances to the broad and multidisciplinary field of nanomaterials-based immunodiagnosis tools, encompassing: (a) the novelty of designing and synthesizing new immunogenic peptides inspired by SARS-CoV-2 virus epitopes using in silico bioinformatics; (b) the peptides induced the immune response in rabbit animal model producing hyperimmune serum; (c) the semi-purified hyperimmune serum rendered effective antibodies to detect SARS-CoV-2 virus in cell suspension; (d) colloidal gold nanoparticles were produced and bioconjugated to the antibodies for qualitative colorimetric detection. As the overall result of this study, it was designed, developed, produced, and validated a new simple, rapid, and sensitive LFA diagnostic test for the SARS-CoV-2 virus using a nanotechnology-based qualitative colorimetric assay, which can be envisioned as promising nanoplatforms for detecting other diseases.

Recombinase Polymerase Amplification Combined with Fluorescence Immunochromatography Assay for On-Site and Ultrasensitive Detection of SARS-CoV-2

This study established a portable and ultrasensitive detection method based on recombinase polymerase amplification (RPA) combined with high-sensitivity multilayer quantum dot (MQD)-based immunochromatographic assay (ICA) to detect the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The RPA-MQD-based ICA method is reported for the first time and has the following advantages: (i) RPA is free from the constraints of instruments and can be promoted in point-of-care testing (POCT) scenarios, (ii) fluorescence ICA enhances the portability of detection operation so that the entire operation time is controlled within 1 h, and (iii) compared with common colorimetric-based RPA-ICA, the proposed assay used MQD to provide strong and quantifiable fluorescence signal, thus enhancing the detection sensitivity. With this strategy, the proposed RPA-MQD-based ICA can amplify and detect the SARS-CoV-2 nucleic acid on-site with a sensitivity of 2 copies/reaction, which is comparable to the sensitivity of commercial reverse transcription quantitative polymerase chain reaction (RT-qPCR) kits. Moreover, the designed primers did not cross-react with other common respiratory viruses, including adenovirus, influenza virus A, and influenza virus B, suggesting high specificity. Thus, the established portable method can sensitively detect SARS-CoV-2 nucleic acid without relying on equipment, having good application prospects in SARS-CoV-2 detection scenarios under non-lab conditions.

Conductive Silver/Carbon Fiber Films for Rapid Detection of Human Coronavirus

Polymerase chain reaction has gained attention since the outbreak of novel coronavirus in 2019. Due to its high specificity and capability for early detection, it is considered a standard method for the diagnosis of infectious diseases. However, the conventional thermocyclers used for nucleic acid amplification are not suitable for point-of-care testing applications, as they require expensive instruments, high-power consumption, and a long turnaround time. To suppress the widespread of the pandemic, there is an urgent need for the development of a rapid, inexpensive, and portable thermal cycler. Therefore, in this paper, we present a conductive silver/carbon fiber film-based thermal cycler with low power consumption (<5 W), efficient heating (~4.5 °C/s), low cost (<USD 200), and handheld size (11.5 × 7.1 × 7.5 mm). The conductive film, which was used as a heating source of the thermal cycler, was fabricated by the electrochemical deposition method. The successful coating of Ag was characterized by a scanning electron microscope and confirmed by energy-dispersive X-ray spectroscopy. The film showed excellent electrical/thermal conductivity and durability. Using our thermal cycler, 35 cycles of amplification were accomplished within 10 min. We also successfully demonstrated the multiplexed detection of various human coronaviruses (e.g., OC43, 229E, and NL63) using our thermal cycler.