Rapid and ultra-sensitive detection of African swine fever virus antibody on site using QDM based-ASFV immunosensor (QAIS)

Development of a fully automated chemiluminescent immunoassay for the quantitative and qualitative detection of antibodies against African swine fever virus p72

African swine fever (ASF), caused by ASF virus (ASFV), is a highly infectious and severe hemorrhagic disease of pigs that causes major economic losses. Currently, no commercial vaccine is available and prevention and control of ASF relies mainly on early diagnosis. Here, a novel automated double antigen sandwich chemiluminescent immunoassay (DAgS-aCLIA) was developed to detect antibodies against ASFV p72 (p72-Ab). For this purpose, recombinant p72 trimer was produced, coupled to magnetic particles as carriers and labeled with acridinium ester as a signal trace. Finally, p72-Ab can be sensitively and rapidly measured on an automated chemiluminescent instrument. For quantitative analysis, a calibration curve was established with a laudable linearity range of 0.21 to 212.0 ng/mL (R2 = 0.9910) and a lower detection limit of 0.15 ng/mL. For qualitative analysis, a cut-off value was set at 1.50 ng/mL with a diagnostic sensitivity of 100.00% and specificity of 98.33%. Furthermore, antibody response to an ASF gene-deleted vaccine candidate can be accurately quantified using this DAgS-aCLIA, as evidenced by early seroconversion as early as 7 days post-immunization and high antibody levels. Compared with available enzyme-linked immunosorbent assays, this DAgS-aCLIA demonstrated a wider linearity range of 4 to 16-fold, and excellent analytical sensitivity and agreement of over 95.60%. In conclusion, our proposed DAgS-aCLIA would be an effective tool to support ASF epidemiological surveillance.IMPORTANCEAfrican swine fever virus (ASFV) is highly contagious in wild boar and domestic pigs. There is currently no vaccine available for ASF, so serological testing is an important diagnostic tool. Traditional enzyme-linked immunosorbent assays provide only qualitative results and are time and resource consuming. This study will develop an automated chemiluminescent immunoassay (CLIA) that can quantitatively and qualitatively detect antibodies to ASFV p72, greatly reducing detection time and labour-intensive operation, and improving detection sensitivity and linearity range. This novel CLIA would serve as a reliable and convenient tool for ASF pandemic surveillance and vaccine development.

Development of quantum dot-based immunochromatographic strip for detection of antibodies against ASFV pp62

ASFV is the only known double-stranded insect-borne DNA virus, which can rapidly infect domestic pigs and wild boars with ticks as transmission medium. Since it was first discovered in 1921, it quickly spread to all parts of the world and brought huge economic losses to the pig industry all over the world. At present, there is still no safe and effective vaccine for ASFV. Here, we developed a quantum-dot labeled antibody test strip for the detection of antibodies against ASFV pp62. The pp62 protein was labeled with quantum dots, and the antibody test strip was developed uses it in a detection mode of labeled antigen-SPA interceptor-monoclonal antibody quality control. The test strip showed high sensitivity, the positive detection limit of the strip was 1: 106 by continuous multiple dilution using the positive standard serum of ASFV antibody as reference. The test strip showed good specificity, and there was no cross reaction with other swine diseases virus (PCV2, PRRSV, CSFV, PPV). Using the detection results of commercialized kit for African swine fever virus as reference, 80 ASFV antibody negative serum and 4 different ASFV antibody positive serum were detected using the ASFV pp62 quantum-dot labeled antibody test strip. The results were consistent with the commercial kit. This study provides a new detection method for the prevention and control of African swine fever.

Development of plate-type and tubular chemiluminescence immunoassay against African swine fever virus p72

African swine fever (ASF) is a highly contagious and fatal viral disease that has caused huge economic losses to the pig and related industries worldwide. At present, rapid, accurate, and sensitive laboratory detection technologies are important means of preventing and controlling ASF. However, because attenuated strains of African swine fever virus (ASFV) are constantly emerging, an ASFV antibody could be used more effectively to investigate the virus and control the disease on pig farms. The isolation of ASFV-specific antibodies is also essential for the diagnosis of ASF. Therefore, in this study, we developed two chemiluminescence immunoassays (CLIAs) to detect antibodies directed against ASFV p72: a traditional plate-type blocking CLIA (p72-CLIA) and an automatic tubular competitive CLIA based on magnetic particles (p72-MPCLIA). We compared the diagnostic performance of these two methods to provide a feasible new method for the effective prevention and control of ASF and the purification of ASFV. The cut-off value, diagnostic sensitivity (Dsn), and diagnostic specificity (Dsp) of p72-CLIA were 40%, 100%, and 99.6%, respectively, in known background serum, whereas those of p72-MPCLIA were 36%, 100%, and 99.6%, respectively. Thus, both methods show good Dsn, Dsp, and repeatability. However, when analytical sensitivity was evaluated, p72-MPCLIA was more sensitive than p72-CLIA or a commercial enzyme-linked immunosorbent assay. More importantly, p72-MPCLIA reduced the detection time to 15 min and allowed fully automated detection. In summary, p72-MPCLIA showed superior diagnostic performance and offered a new tool for detecting ASFV infections in the future. KEY POINTS: • Two chemiluminescence immunoassay (plate-type CLIA and tubular CLIA) methods based on p72 monoclonal antibody (mAb) were developed to detect ASFV antibody. • Both methods show good diagnostic performance (Dsn (100%), Dsp (99.6%), and good repeatability), and p72-MPCLIA detects antibodies against ASFV p72 with high efficiency in just 15 min.

A Portable Fluorescent Lateral Flow Immunoassay Platform for Rapid Detection of FluA

The spread of the FluA virus poses significant public health concerns worldwide. Fluorescent lateral flow immunoassay (LFIA) test strips have emerged as vital tools for the early detection and monitoring of influenza infections. However, existing quantitative virus-detection methods, particularly those utilizing smartphone-based sensing platforms, encounter accessibility challenges in resource-limited areas and among the elderly population. Despite their advantages in speed and portability, these platforms often lack user-friendliness for these demographics, impeding their widespread utilization. To address these challenges, this study proposes leveraging the optical pick-up unit (OPU) sourced from commercial optical drives as a readily available fluorescence excitation module for the quantitative detection of antibodies labeled with quantum-dot fluorescent microspheres. Additionally, we utilize miniaturized and high-performance optical components and 3D-printed parts, along with a customized control system, to develop an affordable point-of-care testing (POCT) device. Within the system, a stepping motor scans the test strip from the T-line to the C-line, enabling the calculation of the fluorescence-intensity ratio between the two lines. This simple yet effective design facilitates rapid and straightforward field or at-home testing for FluA. The proposed prototype platform demonstrates promising performance, achieving a limit of detection (LOD) of 2.91 ng/mL, a total detection time of no more than 15 min, and dimensions of 151 mm × 11.2 mm × 10.8 mm3. We believe that the proposed approach holds great potential for improving access to an accurate influenza diagnosis.

Current detection methods of African swine fever virus

African swine fever (ASF), caused by the African swine fever virus (ASFV), is a highly contagious and notifiable animal disease in domestic pigs and wild boars, as designated by the World Organization for Animal Health (WOAH). The effective diagnosis of ASF holds great importance in promptly controlling its spread due to its increasing prevalence and the continuous emergence of variant strains. This paper offers a comprehensive review of the most common and up-to-date methods established for various genes/proteins associated with ASFV. The discussed methods primarily focus on the detection of viral genomes or particles, as well as the detection of ASFV associated antibodies. It is anticipated that this paper will serve as a reference for choosing appropriate diagnostic methods in diverse application scenarios, while also provide direction for the development of innovative technologies in the future.

Mucosal and cellular immune responses elicited by nasal and intramuscular inoculation with ASFV candidate immunogens

African swine fever (ASF) is an infectious disease caused by African swine fever virus (ASFV) that is highly contagious and has an extremely high mortality rate (infected by virulent strains) among domestic and wild pigs, causing huge economic losses to the pig industry globally. In this study, SDS-PAGE gel bands hybridized with ASFV whole virus protein combined with ASFV-convalescent and ASFV-positive pig serum were identified by mass spectrometry. Six antigens were detected by positive serum reaction bands, and eight antigens were detected in ASFV-convalescent serum. In combination with previous literature reports and proteins corresponding to MHC-II presenting peptides screened from ASFV-positive pig urine conducted in our lab, seven candidate antigens, including KP177R (p22), K78R (p10), CP204L (p30), E183L (p54), B602L (B602L), EP402R-N (CD2V-N) and F317L (F317L), were selected. Subunit-Group 1 was prepared by mixing above-mentioned seven ASFV recombinant proteins with MONTANIDETM1313 VG N mucosal adjuvant and immunizing pigs intranasally and intramuscularly. Subunit-Group 2 was prepared by mixing four ASFV recombinant proteins (p22, p54, CD2V-N1, B602L) with Montanide ISA 51 VG adjuvant and immunizing pigs by intramuscular injection. Anticoagulated whole blood, serum, and oral fluid were collected during immunization for flow cytometry, serum IgG as well as secretory sIgA antibody secretion, and cytokine expression testing to conduct a comprehensive immunogenicity assessment. Both immunogen groups can effectively stimulate the host to produce ideal humoral, mucosal, and cellular immune responses, providing a theoretical basis for subsequent functional studies, such as immunogens challenge protection and elucidation of the pathogenic mechanism of ASFV.

Development of molecular and antigenic-based rapid tests for the identification of African swine fever virus in different tissues

African swine fever (ASF) is a severe haemorrhagic infectious disease affecting suids, thus representing a great economic concern. Considering the importance of the early diagnosis, rapid point of care testing (POCT) for ASF is highly demanded. In this work, we developed two strategies for the rapid onsite diagnosis of ASF, based on Lateral Flow Immunoassay (LFIA) and Recombinase Polymerase Amplification (RPA) techniques. The LFIA was a sandwich-type immunoassay exploiting a monoclonal antibody directed towards the p30 protein of the virus (Mab). The Mab was anchored onto the LFIA membrane to capture the ASFV and was also labelled with gold nanoparticles for staining the antibody-p30 complex. However, the use of the same antibody for capturing and as detector ligand showed a significant competitive effect for antigen binding, so required an experimental design to minimize reciprocal interference and maximize the response. The RPA assay, employing primers to the capsid protein p72 gene and an exonuclease III probe, was performed at 39 °C. The limit of detection of the method was assessed using a plasmid encoding the target gene and resulted in 5 copy/μL. The new LFIA and RPA were applied for ASFV detection in the animal tissues usually analysed by conventional assays (i.e., real-time PCR), such as kidney, spleen, and lymph nodes. A simple and universal virus extraction protocol was applied for sample preparation, followed by DNA extraction and purification for the RPA. The LFIA only required the addition of 3% H2O2 to limit matrix interference and prevent false positive results. The two rapid methods (25 min and 15 min were needed to complete the analysis for RPA and LFIA, respectively) showed high diagnostic specificity (100%) and sensitivity (93% and 87% for LFIA and RPA, respectively) for samples with high viral load (Ct < 27). False negative results were observed for samples with low viral load (Ct > 28) and/or also containing specific antibodies to ASFV, which decreased antigen availability and were indicative of a chronic, poorly transmissible infection. The simple and rapid sample preparation and the diagnostic performance of the LFIA suggested its large practical applicability for POC diagnosis of ASF.

Method for the Rapid Detection of SARS-CoV-2-Neutralizing Antibodies Using a Nanogel-Based Surface Plasmon Resonance Biosensor

The efficacy of coronavirus disease 2019 (COVID-19) vaccination is closely related to the serum levels of SARS-CoV-2-neutralizing antibodies (NAb) that bind to the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. Therefore, the rapid and quantitative measurement of SARS-CoV-2 NAb in the sera of vaccinated individuals is essential to develop an effective vaccine and further achieve population immunity, that is, herd immunity. The plaque reduction neutralization test, the gold standard for NAb effectiveness in serological tests, is accurate but requires biosafety level 3 facilities because of the use of the virus, which hampers its application in common laboratories and clinical practice. Here, we developed a bioresponsive nanogel-based surface plasmon resonance (nSPR) platform that detects SARS-CoV-2 NAb in clinical samples without complicated pretreatment. We found that multivalent protein binding (MPB) between the nanogel-conjugated RBD protein and SARS-CoV-2 NAb yields significantly enhanced SPR signals compared to the nonspecific interference from serum proteins in the nSPR assay. The excellence of our nanogel-based SARS-CoV-2 NAb test is due to its selectivity for NAb, with resistance to all other proteins, allowing the rapid detection and quantification of NAbs in each individual. Importantly, this nSPR assay provides a NAb detection platform for easier and safer COVID-19 vaccination strategies.

Novel Epitopes Mapping of African Swine Fever Virus CP312R Protein Using Monoclonal Antibodies

African Swine Fever (ASF) is a highly contagious and lethal pig disease and poses a huge threat to the pig industry worldwide. ASF virus (ASFV) encodes more than 150 different proteins, but the biological properties of most viral proteins are still unknown. ASFV CP312R protein has been proven to be one of the most immunogenic proteins during ASFV infection in pigs; however, its specific epitopes have yet to be identified. In this study, we verified the immunogenicity of CP312R protein in the sera from attenuated ASFV-inoculated pigs. We generated seven anti-ASFV CP312R mouse monoclonal antibodies (mAbs) from mice immunized with recombinant CP312R protein (rCP312R). All seven mAbs are the IgG2b-Kappa isotype and specifically interacted with the CP312R protein expressed in various cells that were infected by ASFVs or transfected with plasmid CP312R. The epitope mapping was performed by using these characterized mAbs and the peptide scanning (Pepscan) method followed by Western blot. As a result, two antigenic determinant regions were identified: two of the seven mAbs recognized the ¹²²KNEQGEEIYP¹³¹ amino acids, and the remaining five mAbs recognized the ⁷⁸DEEVIRMNAE⁸⁷ amino acids of the CP312R protein. These antigenic determinants of CP312R are conserved in different ASFV strains of seven genotypes. By using the characterized mAb, confocal microscopy observation revealed that the CP312R was mainly localized in the cytoplasm and, to some extent, in nuclei and on the nuclear membrane of infected host cells. In summary, our results benefit our understanding on the antigenic regions of ASFV CP312R and help to develop better serological diagnosis of ASF and vaccine research.

Portable high-throughput multimodal immunoassay platform for rapid on-site COVID-19 diagnostics

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a causal agent of Coronavirus Disease 2019 (COVID-19) has led to the global pandemic. Though the real-time reverse transcription polymerase chain reaction (RT-PCR) acting as a gold-standard method has been widely used for COVID-19 diagnostics, it can hardly support rapid on-site applications or monitor the stage of disease development as well as to identify the infection and immune status of rehabilitation patients. To suit rapid on-site COVID-19 diagnostics under various application scenarios with an all-in-one device and simple detection reagents, we propose a high-throughput multimodal immunoassay platform with fluorescent, colorimetric, and chemiluminescent immunoassays on the same portable device and a multimodal reporter probe using quantum dot (QD) microspheres modified with horseradish peroxidase (HRP) coupled with goat anti-human IgG. The recombinant nucleocapsid protein fixed on a 96-well plate works as the capture probe. In the condition with the target under detection, both reporter and capture probes can be bound by such target. When illuminated by excitation light, fluorescence signals from QD microspheres can be collected for target quantification often at a fast speed. Additionally, when pursuing simple detection without using any sensing devices, HRP-catalyzed TMB colorimetric immunoassay is employed; and when pursuing highly sensitive detection, HRP-catalyzed luminol chemiluminescent immunoassay is established. Verified by the anti-SARS-CoV-2 N humanized antibody, the sensitivities of colorimetric, fluorescent, and chemiluminescent immunoassays are respectively 20, 80, and 640 times more sensitive than that of the lateral flow colloidal gold immunoassay strip. Additionally, such a platform can simultaneously detect multiple samples at the same time thus supporting high-throughput sensing; and all these detecting operations can be implemented on-site within 50 min relying on field-operable processing and field-portable devices. Such a high-throughput multimodal immunoassay platform can provide a new all-in-one solution for rapid on-site diagnostics of COVID-19 for different detecting purposes.

One-Step Rapid and Sensitive ASFV p30 Antibody Detection via Nanoplasmonic Biosensors

African swine fever (ASF) is one of the most serious transnational swine diseases in the world. The case fatality rate of susceptible pigs is up to 100%. Currently, no commercial vaccine is available, so the prevention and control of ASF mainly relies on early diagnosis and culling of infected pigs. As the ASF virus continues to evolve, develop, and diversify, nucleic acid testing becomes less efficient. Here, we developed a method for the rapid and direct optical measurement of African swine fever virus (ASFV) antibody in vitro. This one-step procedure requires nearly no sample preparation and involves p30 protein-specific label-free integration into standard 96-well plates. Using a nanoplasmonic biosensor with extraordinary optical transmission (EOT) effect, one-step sample addition, ASFV antibody was detected within 20 min. The positive antibody showed a satisfactory sensitivity and linear relationship in the dilution ratio of 1:100-1:16000. It was used for the detection of clinical serum samples with a coincidence rate of 96.6%. The measurement results can be automatically analyzed and displayed on a conventional microplate meter computer and connected device. Our detection method can be widely applied in point-of-care testing (POCT) of ASFV antibody in pig farms. IMPORTANCE African swine fever (ASF) is a serious transnational disease caused by the African swine fever virus (ASFV), which is highly contagious in wild boars and domestic pigs. There is currently no available vaccine for ASF; therefore, development efforts are a key priority as ASFV continues to evolve and diversify. The ASF antibody rapid detection platform comprising the nanoplasmonic biosensor with extraordinary optical transmission effect can greatly reduce the detection time and improve detection flux while maintaining detection sensitivity and specificity. The one-step sample addition can effectively avoid cross contamination of samples in the detection process. The detection method provides a solution for the rapid and accurate real-time monitoring of ASF in pig farms.

Rapid and sensitive detection of African swine fever virus in pork using recombinase aided amplification combined with QDMs-based test strip

African swine fever virus (ASFV) is the pathogen of African swine fever, a highly contagious and fatal disease of wild boar and domestic pigs. The flow of ASFV through pork products is more concealed, higher risky, and more difficult to prevent and control. Presently, on-site ASFV detection methods in preclinical infected pigs and circulated pork products are lacking. Here, fluorescent test strip-based rapid ASFV detection method in pork was established combined with recombinase aided amplification (RAA) and quantum dot microspheres (QDMs). This method is specific to ASFV with no cross-reactivity to pseudorabies virus (PRV), porcine circovirus type 2 (PCV2), and porcine reproductive and respiratory syndrome virus (PRRSV). The method also showed highly sensitivity with a detection limit of 1 copy for ASFV plasmid templates containing B646L gene and 100 copies/g for DNA extracts from clinical pork samples within a short detection time of less than 25 min. Additionally, the method showed 99.17% consistency with real-time PCR in the ASFV detection of 120 clinical pork samples. Overall, the QDMs-based test strip method provides specific, sensitive, rapid, and simple detection of ASFV in pork, which may contribute to maintain the food safety of pork products, and facilitate ASFV traceability and prevention. Rapid and sensitive detection of African swine fever virus in pork by QDMs based test strip assay.

Lateral Flow Assay for the Detection of African Swine Fever Virus Antibodies Using Gold Nanoparticle-Labeled Acid-Treated p72

African swine fever is a widespread and highly contagious disease in the porcine population, which is caused by African swine fever virus (ASFV). The PCR and ELISA detection methods are the main conventional diagnostic methods for ASFV antigen/antibody detection in the field. However, these methods have limitations of expensive equipment, trained technicians, and time-consuming results. Thus, a rapid, inexpensive, accurate and on-site detection method is urgently needed. Here we describe a double-antigen-sandwich lateral-flow assay based on gold nanoparticle-conjugated ASFV major capsid protein p72, which can detect ASFV antibody in serum samples with high sensitivity and specificity in 10 min and the results can be determined by naked eyes. A lateral flow assay was established by using yeast-expressed and acid-treated ASFV p72 conjugated with gold nanoparticles, which are synthesized by seeding method. A high coincidence (97.8%) of the assay was determined using clinical serum compared to a commercial ELISA kit. In addition, our lateral flow strip can detect as far as 1:10,000 diluted clinically positive serum for demonstration of high sensitivity. In summary, the assay developed here was shown to be rapid, inexpensive, accurate and highly selective. It represents a reliable method for on-site ASFV antibody detection and may help to control the ASFV pandemic.