Comparison of double antigen sandwich and indirect enzyme-linked immunosorbent assay for the diagnosis of hepatitis C virus antibodies

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.

WITHDRAWN: Development of a double-antigen sandwich ELISA for African swine fever virus antibody detection based on K205R protein

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/policies/article-withdrawal.

Development of an effective one-step double-antigen sandwich ELISA based on p72 to detect antibodies against African swine fever virus

African swine fever (ASF), caused by ASF virus (ASFV), is a highly contagious and lethal disease of domestic pigs leading to tremendous economic losses. As there are no vaccines and drugs available. An effective diagnosis to eliminate ASFV-infected pigs is a crucial strategy to prevent and control ASF. To this end, ASFV capsid protein p72 was expressed using Chinese hamster ovary (CHO) cells and subsequently conjugated with horseradish peroxidase (HRP) to develop a one-step double-antigen sandwich enzyme-linked immunosorbent assay (one-step DAgS-ELISA). The performance of this ELISA for detecting ASFV antibodies was evaluated. Overall, a diagnostic sensitivity of 97.96% and specificity of 98.96% was achieved when the cutoff value was set to 0.25. No cross-reaction with healthy pig serum and other swine viruses was observed. The coefficients of variation of the intra-assay and inter-assay were both <10%. Importantly, this ELISA could detect antibodies in standard serum with 12,800-fold dilution, and seroconversion started from the 7th day post-inoculation (dpi), showing excellent analytical sensitivity and great utility. Furthermore, compared to the commercial kit, this ELISA had a good agreement and significantly shorter operation time. Collectively, a novel one-step DAgS-ELISA for detecting antibodies against ASFV is developed, which will be reliable and convenient to monitor ASFV infection.

Development of a novel double-antibody sandwich quantitative ELISA for detecting SADS-CoV infection

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is an emerging swine enteric alphacoronavirus that can cause acute diarrhea, vomiting, dehydration, and death of newborn piglets. In this study, we developed a double-antibody sandwich quantitative enzyme-linked immunosorbent assay (DAS-qELISA) for detection of SADS-CoV by using an anti-SADS-CoV N protein rabbit polyclonal antibody (PAb) and a specific monoclonal antibody (MAb) 6E8 against the SADS-CoV N protein. The PAb was used as the capture antibodies and HRP-labeled 6E8 as the detector antibody. The detection limit of the developed DAS-qELISA assay was 1 ng/mL of purified antigen and 10^1.08TCID₅₀/mL of SADS-CoV, respectively. Specificity assays showed that the developed DAS-qELISA has no cross-reactivity with other swine enteric coronaviruses, such as porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine deltacoronavirus (PDCoV). Three-day-old piglets were challenged with SADS-CoV and collected anal swab samples which were screened for the presence of SADS-CoV by using DAS-qELISA and reverse transcriptase PCR (RT-PCR). The coincidence rate of the DAS-qELISA and RT-PCR was 93.93%, and the kappa value was 0.85, indicating that DAS-qELISA is a reliable method for applying antigen detection of clinical samples. KEY POINTS: • The first double-antibody sandwich quantitative enzyme-linked immunosorbent assay for detection SADS-CoV infection. • The custom ELISA is useful for controlling the SADS-CoV spread.

Quantum dots assembly enhanced and dual-antigen sandwich structured lateral flow immunoassay of SARS-CoV-2 antibody with simultaneously high sensitivity and specificity

Exploring reliable and highly-sensitive SARS-CoV-2 antibody diagnosis by point-of-care (POC) manner, holds great public health significance for extensive COVID-19 screening and controlling. Unfortunately, the currently applied gold based lateral flow immunoassay (GLFIA) may expose both false-negative and false-positive interpretations owing to the sensitivity and specificity limitations, which may cause significant risk and waste of public resources for large population screening. To simultaneously overcome the drawbacks of GLFIA, a novel fluorescent LFIA based on signal amplification and dual-antigen sandwich structure was established with largely improved sensitivity and specificity. The compact three-dimensional incorporation of hydrophobic quantum dots within dendritic affinity templates and multilayer surface derivation guaranteed a high and robust fluorescence of single label, which lowered the false negative rate of GLFIA prominently. A dual-antigen sandwich structure using labeled/immobilized SARS-CoV-2 spike receptor binding domain antigen for capturing total human SARS-CoV-2 antibody was developed, instead of general indirect antibody capturing approach, to reduce the false positive rate of GLFIA. Over 300 cases of COVID-19 negative and 97 cases of COVID-19 positive samples, the current assay revealed a 100% sensitivity and 100% specificity confirmed by both polymerase chain reaction (PCR) and chemiluminescence immunoassay (CLIA), compared with the considerable misinterpretation cases by currently applied GLFIA. The quantitative results verified by receiver operating characteristic curve and other statistical analysis indicated a well-distinguished positive/negative sample groups. The proposed strategy is highly sensitive towards low concentrated SARS-CoV-2 antibody serums and highly specific towards serums from COVID-19 negative persons and patients infected by other viruses.

A Fluorescent Biosensor for Sensitive Detection of Salmonella Typhimurium Using Low-Gradient Magnetic Field and Deep Learning via Faster Region-Based Convolutional Neural Network

In this study, a fluorescent biosensor was developed for the sensitive detection of Salmonella typhimurium using a low-gradient magnetic field and deep learning via faster region-based convolutional neural networks (R-CNN) to recognize the fluorescent spots on the bacterial cells. First, magnetic nanobeads (MNBs) coated with capture antibodies were used to separate target bacteria from the sample background, resulting in the formation of magnetic bacteria. Then, fluorescein isothiocyanate fluorescent microspheres (FITC-FMs) modified with detection antibodies were used to label the magnetic bacteria, resulting in the formation of fluorescent bacteria. After the fluorescent bacteria were attracted against the bottom of an ELISA well using a low-gradient magnetic field, resulting in the conversion from a three-dimensional (spatial) distribution of the fluorescent bacteria to a two-dimensional (planar) distribution, the images of the fluorescent bacteria were finally collected using a high-resolution fluorescence microscope and processed using the faster R-CNN algorithm to calculate the number of the fluorescent spots for the determination of target bacteria. Under the optimal conditions, this biosensor was able to quantitatively detect Salmonella typhimurium from 6.9 × 10¹ to 1.1 × 10³ CFU/mL within 2.5 h with the lower detection limit of 55 CFU/mL. The fluorescent biosensor has the potential to simultaneously detect multiple types of foodborne bacteria using MNBs coated with their capture antibodies and different fluorescent microspheres modified with their detection antibodies.

Switching from Multiplex to Multimodal Colorimetric Lateral Flow Immunosensor

Multiplex lateral flow immunoassay (LFIA) is largely used for point-of-care testing to detect different pathogens or biomarkers in a single device. The increasing demand for multitargeting diagnostics requires multi-informative single tests. In this study, we demonstrated three strategies to upgrade standard multiplex LFIA to multimodal capacity. As a proof-of-concept, we applied the strategies to the differential diagnosis of Human Immunodeficiency Virus (HIV) infection, a widespread pathogen, for which conventional multiplex LFIA testing is well-established. In the new two-parameter LFIA (x2LFIA), we exploited color encoding, in which the binding of multiple targets occurs in one reactive band and the color of the probe reveals which one is present in the sample. By combining the sequential alignment of several reactive zones along the membrane of the LFIA strip and gold nanoparticles and gold nanostars for the differential visualization, in this demonstration, the x2LFIA can furnish information on HIV serotype and stage of infection in a single device. Three immunosensors were designed. The use of bioreagents as the capturing ligand anchored onto the membrane or as the detection ligand labelled with gold nanomaterials affected the performance of the x2LFIA. Higher detectability was achieved by the format involving the HIV-specific antigens as capturing agent and labelled secondary bioligands (anti-human immunoglobulins M and protein G) as the probes.