Bifunctional Au@Pt/Au nanoparticles as electrochemiluminescence signaling probes for SARS-CoV-2 detection.

A novel immunosensor based on electrochemiluminescence resonance energy transfer (ECL-RET) for the sensitive determination of N protein of the SARS-CoV-2 coronavirus is described. For this purpose, bifunctional core@shell nanoparticles composed of a Pt-coated Au core and finally decorated with small Au inlays (Au@Pt/Au NPs) have been synthesized to act as ECL acceptor, using [Ru (bpy)3]2+ as ECL donor. These nanoparticles are efficient signaling probes in the immunosensor developed. The proposed ECL-RET immunosensor has a wide linear response to the concentration of N protein of the SARS-CoV-2 coronavirus with a detection limit of 1.27 pg/mL. Moreover, it has a high stability and shows no response to other proteins related to different virus. The immunosensor has achieved the quantification of N protein of the SARS-CoV-2 coronavirus in saliva samples. Results are consistent with those provided by a commercial colorimetric ELISA kit. Therefore, the developed immunosensor provides a feasible and reliable tool for early and effective detection of the virus to protect the population.

Electrochemiluminescence resonance energy transfer biosensing platform between g-C3N4 nanosheet and Ru-SiO2@FA for dual-wavelength ratiometric detection of SARS-CoV-2 RdRp gene.

Rational detection of syndrome coronavirus 2 (SARS-CoV-2) is crucial to prevention, control, and treatment of disease. Herein, a dual-wavelength ratiometric electrochemiluminescence (ECL) biosensor based on resonance energy transfer (RET) between g-C3N4 nanosheets and Ru-SiO2@folic acid (FA) nanomaterials was designed to realize ultrasensitive detection of SARS-CoV-2 virus (RdRp gene). Firstly, the unique g-C3N4 nanosheets displayed very intense and stable ECL at 460 nm, then the triple helix DNA was stably and vertically bound to g-C3N4 on electrode by high binding affinity between ssDNA and g-C3N4. Meanwhile, trace amounts of target genes were converted to a large number of output by three-dimensional (3D) DNA walker multiple amplification, and the output bridged a multifunctional probe Ru-SiO2@FA to electrode. Ru-SiO2@FA not only showed high ECL at 620 nm, but also effectively quenched g-C3N4 ECL. As a result, ECL decreased at 460 nm and increased at 620 nm, which was used to design a rational ECL biosensor for detection of SARS gene. The results show that the biosensor has excellent detection sensitivity for RdRp gene with a dynamic detection range of 1 fM to 10 nM and a limit of detection (LOD) of 0.18 fM. The dual-wavelength ratio ECL biosensor has inestimable value and application prospects in the fields of biosensing and clinical diagnosis.

Rapid determination of SARS-CoV-2 nucleocapsid proteins based on 2D/2D MXene/P-BiOCl/Ru(bpy)32+ heterojunction composites to enhance electrochemiluminescence performance.

At the end of 2019, the novel coronavirus disease 2019 (COVID-19), a cluster of atypical pneumonia caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been known as a highly contagious disease. Herein, we report the MXene/P-BiOCl/Ru(bpy)32+ heterojunction composite to construct an electrochemiluminescence (ECL) immunosensor for SARS-CoV-2 nucleocapsid protein (CoVNP) determination. Two-dimensional (2D) material ultrathin phosphorus-doped bismuth oxychloride (P-BiOCl) is exploited and first applied in ECL. 2D architectures MXene not only act as "soft substrate" to improve the properties of P-BiOCl, but also synergistically work with P-BiOCl. Owing to the inimitable set of bulk and interfacial properties, intrinsic high electrochemical conductivity, hydrophilicity and good biocompatible of 2D/2D MXene/P-BiOCl/Ru(bpy)32+, this as-exploited heterojunction composite is an efficient signal amplifier and co-reaction accelerator in the presence of tri-n-propylamine (TPA) as a coreactant. The proposed MXene/P-BiOCl/Ru(bpy)32+-TPA system exhibits a high and stable ECL signal and achieves ECL emission quenching for "signal on-off" recognition of CoVNP. Fascinatingly, the constructed ECL biosensor towards CoVNP allows a wide linear concentration range from 1 fg/mL to 10 ng/mL and a low limit of detection (LOD) of 0.49 fg/mL (S/N = 3). Furthermore, this presented strategy sheds light on designing a highly efficient ECL nanostructure through the combination of 2D MXene architectures with 2D semiconductor materials in the field of nanomedicine. This ECL biosensor can successfully detect CoVNP in human serum, which can promote the prosperity and development of diagnostic methods of SARS-CoV-2.

Charge-Dependent Signal Changes for Label-Free Electrochemiluminescence Immunoassays.

Label-free electrochemiluminescence (ECL) immunoassays (lf-ECLIA), based on biomarker-induced ECL signal changes, have attracted increasing attention due to the simple, rapid, and low-cost detection of biomarkers without secondary antibodies and complicated labeling procedures. However, the interaction rule and mechanism between analytical interfaces and biomarkers have rarely been explored. Herein, the interactions between biomarkers and analytical interfaces constructed by assembly of a nanoluminophore and antibody-functionalized gold nanoparticles on an indium tin oxide electrode were studied. The nanoluminophore was synthesized by mixing Cu2+/l-cysteine chelate and N-(4-Aminobutyl)-N-ethylisoluminol-bifunctionalized gold nanoparticles with chitosan. It was found that positively charged biomarkers increased the ECL intensity, whereas negatively charged biomarkers decreased the ECL intensity. The assembly pH influenced the biomarker charges, which determined the ECL enhancement or inhibition. The detection pH only affected the ECL intensity but not the ECL changing trends. Based on the ECL signal changes, a charge-dependent lf-ECLIA was established, which exhibited inhibition responses to negatively charged human immunoglobulin G and copeptin and enhancement responses to positively charged cardiac troponin I, heart-type fatty acid binding protein, brain natriuretic peptide, and SARS-CoV-2 N protein. The linear range was 0.1-1000 pg/mL, and the detection limits were distributed in 0.024-0.091 pg/mL. Besides, a mechanism of the charge-dependent ECL enhancement and inhibition effects is proposed, which is very important for the development of new lf-ECLIA methodologies.

Hydrophobic Localized Enrichment of Co-reactants to Enhance Electrochemiluminescence of Conjugated Polymers for Detecting SARS-CoV-2 Nucleocapsid Proteins.

The enrichment of co-reactants is one of the keys to improving the sensitivity of electrochemiluminescence (ECL) detection. This work developed a novel hydrophobic localized enrichment strategy of co-reactants utilizing the inner hydrophobic cavity of ß-cyclodextrin (ß-CD). Pt nanoparticles (Pt NPs) were grown in situ on the coordination sites for metal ions of ß-CD to prepare the ß-CD-Pt nanocomposite, which could not only enrich co-reactant 3-(dibutylamino) propylamine (TDBA) highly efficiently through its hydrophobic cavity but also immobilize TDBA via the Pt-N bond. Meanwhile, the carboxyl-functionalized poly[2,5-dioctyl-1,4-phenylene] (PDP) polymer nanoparticles (PNPs) were developed as excellent ECL luminophores. With SARS-CoV-2 nucleocapsid protein (ncovNP) as a model protein, the TDBA-ß-CD-Pt nanocomposite combined PDP PNPs to construct a biosensor for ncovNP determination. The PDP PNPs were modified onto the surface of a glassy carbon electrode (GCE) to capture the first antibody (Ab1) and further capture antigen and secondary antibody complexes (TDBA-ß-CD-Pt@Ab2). The resultant biosensor with a sandwich structure achieved a highly sensitive detection of ncovNP with a detection limit of 22 fg/mL. TDBA-ß-CD-Pt shared with an inspiration in hydrophobic localized enrichment of co-reactants for improving the sensitivity of ECL detection. The luminophore PDP PNPs integrated TDBA-ß-CD-Pt to provide a promising and sensitive ECL platform, offering a new method for ncovNP detection.

A protease-activatable luminescent biosensor and reporter cell line for authentic SARS-CoV-2 infection.

Efforts to define serological correlates of protection against COVID-19 have been hampered by the lack of a simple, scalable, standardised assay for SARS-CoV-2 infection and antibody neutralisation. Plaque assays remain the gold standard, but are impractical for high-throughput screening. In this study, we show that expression of viral proteases may be used to quantitate infected cells. Our assays exploit the cleavage of specific oligopeptide linkers, leading to the activation of cell-based optical biosensors. First, we characterise these biosensors using recombinant SARS-CoV-2 proteases. Next, we confirm their ability to detect viral protease expression during replication of authentic virus. Finally, we generate reporter cells stably expressing an optimised luciferase-based biosensor, enabling viral infection to be measured within 24 h in a 96- or 384-well plate format, including variants of concern. We have therefore developed a luminescent SARS-CoV-2 reporter cell line, and demonstrated its utility for the relative quantitation of infectious virus and titration of neutralising antibodies.

An Evolving Technology That Integrates Classical Methods with Continuous Technological Developments: Thin-Layer Chromatography Bioautography.

Thin-layer chromatography (TLC) bioautography is an evolving technology that integrates the separation and analysis technology of TLC with biological activity detection technology, which has shown a steep rise in popularity over the past few decades. It connects TLC with convenient, economic and intuitive features and bioautography with high levels of sensitivity and specificity. In this study, we discuss the research progress of TLC bioautography and then establish a definite timeline to introduce it. This review summarizes known TLC bioautography types and practical applications for determining antibacterial, antifungal, antitumor and antioxidant compounds and for inhibiting glucosidase, pancreatic lipase, tyrosinase and cholinesterase activity constitutes. Nowadays, especially during the COVID-19 pandemic, it is important to identify original, natural products with anti-COVID potential compounds from Chinese traditional medicine and natural medicinal plants. We also give an account of detection techniques, including in situ and ex situ techniques; even in situ ion sources represent a major reform. Considering the current technical innovations, we propose that the technology will make more progress in TLC plates with higher separation and detection technology with a more portable and extensive scope of application. We believe this technology will be diffusely applied in medicine, biology, agriculture, animal husbandry, garden forestry, environmental management and other fields in the future.

Chemiluminescence Immunoassay Based Serological Immunoassays for Detection of SARS-CoV-2 Neutralizing Antibodies in COVID-19 Convalescent Patients and Vaccinated Population.

The development of rapid serological detection methods re urgently needed for determination of neutralizing antibodies in sera. In this study, four rapid methods (ACE2-RBD inhibition assay, S1-IgG detection, RBD-IgG detection, and N-IgG detection) were established and evaluated based on chemiluminescence technology. For the first time, a broadly neutralizing antibody with high affinity was used as a standard for the quantitative detection of SARS-CoV-2 specific neutralizing antibodies in human sera. Sera from COVID-19 convalescent patients (N = 119), vaccinated donors (N = 86), and healthy donors (N = 299) confirmed by microneutralization test (MNT) were used to evaluate the above methods. The result showed that the ACE2-RBD inhibition assay calculated with either ACE2-RBD binding inhibition percentage rate or ACE2-RBD inhibiting antibody concentration were strongly correlated with MNT (r ≥ 0.78, p < 0.0001) and also highly consistent with MNT (Kappa Value ≥ 0.94, p < 0.01). There was also a strong correlation between the two evaluation indices (r ≥ 0.99, p < 0.0001). Meanwhile, S1-IgG and RBD-IgG quantitative detection were also significantly correlated with MNT (r ≥ 0.73, p < 0.0001), and both methods were highly correlated with each other (r ≥ 0.95, p < 0.0001). However, the concentration of N-IgG antibodies showed a lower correlation with the MNT results (r < 0.49, p < 0.0001). The diagnostic assays presented here could be used for the evaluation of SARS-CoV-2 vaccine immunization effect and serological diagnosis of COVID-19 patients, and could also have guiding significance for establishing other rapid serological methods to surrogate neutralization tests for SARS-CoV-2.

Performance characteristics of five SARS-CoV-2 serological assays: Clinical utility in health-care workers.

STUDY OBJECTIVE: SARS-CoV-2, which causes coronavirus disease (COVID-19), continues to cause significant morbidity and mortality. The diagnosis of acute infection relies on reverse transcription-polymerase chain reaction (RT-PCR)-based viral detection. The objective of this study was to evaluate the optimal serological testing strategy for anti-SARS-CoV-2 antibodies which provides an important indicator of prior infection and potential short-term immunity. METHODS: The sensitivity and specificity of four different ELISA assays (Euroimmun IgG, Euroimmun NCP-IgG, Fortress and DIAsource) and one CLIA assay (Roche ELECSYS) were evaluated in 423 samples; 137 patients with confirmed RT-PCR COVID-19 infection (true positives), and 100 pre-pandemic samples collected prior to October 2019 (true negatives). A further 186 samples were collected from health-care staff and analysed by all five assays. RESULTS: The Fortress ELISA assay demonstrated the highest sensitivity and specificity followed by the Roche ECLIA assay. The highest overall sensitivity came from the assays that measured total antibody (IgM-IgG combined) and the three assays that performed the best (Fortress, Roche, Euroimmun IgG) all have different antigens as their target proteins which suggests that antigen target does not affect assay performance. In mildly symptomatic participants with either a negative RT-PCR or no RT-PCR performed, 16.76% had detectable antibodies suggesting previous infection. CONCLUSIONS: We recommend a combined testing strategy utilizing assays with different antigenic targets using the fully automated Roche ECLIA assay and confirming discordant samples with the Fortress Total Antibody ELISA assay. This study provides an important indicator of prior infection in symptomatic and asymptomatic individuals.

Serologic Response to SARS-CoV-2 in COVID-19 Patients with Different Severity.

The immense patient number caused by coronavirus disease 2019 (COVID-19) global pandemic brings the urge for more knowledge about its immunological features, including the profile of basic immune parameters. In this study, eighty-eight reported COVID-19 patients in Wuhan were recruited from January to February, 2020, including 32 severe/critical cases and 56 mild/moderate cases. Their mean age was 56.43 years (range 17-83) and gender ratio (male/female) was 43:45. We tested SARS-CoV-2 RNA with commercial kits, investigated the level of serologic IgM and IgG antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using magnetic particle chemiluminescence immunoassays, and compared the results of serologic tests and nucleic acid test (NAT). Among 88 patients, 95.45% were confirmed as positive by the combination of NAT and antibody test, which was significantly higher (P < 0.001) than by single nucleic acid test (73.86%) or serologic test (65.91%). Then the correlation between temporal profile and the level of antibody response was analyzed. It showed that seroconversion started on day 5 after disease onset and IgG level was rose earlier than IgM. Comparison between patients with different disease severity suggested early seroconversion and high antibody titer were linked with less severe clinical symptoms. These results supported the combination of serologic testing and NAT in routine COVID-19 diagnosis and provided evidence on the temporal profile of antibody response in patients with different disease severity.

Clinical usefulness of fully automated chemiluminescent immunoassay for quantitative antibody measurements in COVID-19 patients.

Since December 2019, we have been in the battlefield with a new threat to the humanity, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), characterized by viral pneumonia. It may be asymptomatic or cause various symptoms, ranging from flu-like symptoms to acute respiratory distress syndrome and eventually death. At present, the only reliable test for COVID-19 diagnosis is quantitative reverse transcriptase-polymerase chain reaction. Assessing the immune response against SARS-CoV-2 could increase the detection sensitivity of infected population. Hereby, we report the performances of a fully automated chemiluminescent immunoassay (CLIA) on 276 serum samples. One hundred samples obtained from COVID-19 negative subjects (COVID-19 free) were analyzed to evaluate the diagnostic specificity of antibody (Ab) detection. Thereafter, 176 samples obtained from 125 patients with confirmed COVID-19 (COVID-19 patients) were selected to assess the diagnostic sensitivity of the CLIA. All samples were analyzed on MAGLUMI 800 platform. All COVID-19 free samples had Ab levels below the cutoff values. Hence, the diagnostic specificity was estimated at 100% (95% confidence interval [CI] = 96.3-100.0; positive predictive value = 100%). By the 18th day from the onset of symptoms, we reached an optimal diagnostic sensitivity (more than 95.0%) In fact, the diagnostic sensitivity increased over time and between 15 and 25 days after symptoms onset, reached 95.5% (95% CI = 84.9-99.2). The new automated CLIA analyzer appeared to be a robust and reliable method to measure specific Ab against COVID-19 at high throughput. Our data suggest that combining Ab and nucleic acid detection could increase diagnostic sensitivity.

Validation and performance comparison of three SARS-CoV-2 antibody assays.

Serology testing of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is increasingly being used during the current pandemic of coronavirus disease 2019 (COVID-19), although its clinical and epidemiologic utilities are still debatable. Characterizing these assays provides scientific basis to best use them. The current study assessed one chemiluminescent assay (Abbott COVID-2 IgG) and two lateral flow assays (STANDARD Q [SQ] IgM/IgG Duo and Wondfo total antibody test) using 113 blood samples from 71 PCR-confirmed COVID-19 hospitalized patients, 119 samples with potential cross-reactions, and 1068 negative controls including 942 pre-pandemic samples. SARS-CoV-2 IgM antibodies became detectable 3-4 days post-symptom onset using SQ IgM test and IgG antibodies were first detected 5-6 days post-onset using SQ IgG. Abbott IgG and Wondfo Total were able to detect antibodies 7 to 8 days post-onset. After 14 days post-symptom onset, the SQ IgG, Abbott IgG and Wondfo Total tests were able to detect antibodies from 100% of the PCR-confirmed patients in this series; 87.5% sensitivity for SQ IgM. Overall agreement was 88.5% between SQ IgM/IgG and Wondfo Total and 94.6% between SQ IgG and Abbott IgG. No cross-reaction due to recent sera with three of the endemic coronaviruses was observed. Viral hepatitis and autoimmune samples were the main source of limited cross-reactions. The specificities were 100% for SQ IgG and Wondfo Total, 99.62% for Abbott IgG, and 98.87% for SQ IgM. These findings demonstrated high sensitivity and specificity of appropriately validated SARS-CoV-2 serologic assays with implications for clinical use and epidemiological seroprevalence studies.

Interpretive discrepancies caused by target values inter-batch variations in chemiluminescence immunoassay for SARS-CoV-2 IgM/IgG by MAGLUMI.

Plasma specimens from coronavirus disease 2019 patients were double-tested for anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies by two different batches of MAGLUMI 2019-nCov immunoglobulin M/immunoglobulin G (IgM/IgG) assays to evaluate IgM/IgG levels, qualitative interpretation, antibody kinetics, and linearity of diluted specimen. Here we show that (i) high-level IgM specimens need to be diluted with negative human plasma but not kit diluents and (ii) measured anti-SARS-CoV-2 IgM/IgG concentrations are substantially higher with later marketed immunoassay batch leading to (iii) the change of qualitative interpretation (positive vs. negative) in 12.3% of specimens measured for IgM, (iv) the informative time-course pattern of antibody production only when data from different immunoassay batches are not combined.

Clinical Performance of SARS-CoV-2 IgG and IgM Tests Using an Automated Chemiluminescent Assay.

Serology tests for viral antibodies provide an important tool to support nucleic acid testing for diagnosis of the novel coronavirus disease 2019 (COVID-19) and is useful for documenting previous exposures to SARS-CoV-2, the etiological agent of COVID-19. The sensitivities of the chemiluminescent SARS-CoV-2 IgG/IgM immunoassay were assessed by using serum samples collected from 728 patients testing positive for SARS-CoV-2 RNA. The specificity was evaluated on a panel of 60 serum samples from non-COVID-19 patients with high levels of rheumatoid factor, antinuclear antibody, or antibodies against Epstein-Barr virus (EBV), cytomegalovirus (CMV), mycoplasma pneumonia, human respiratory syncytial virus (RSV), adenovirus, influenza A or influenza B. The imprecision and interference were assessed by adopting the Clinical and Laboratory Standards Institute (CLSI) EP15-A2 and EP7-A2, respectively. Sensitivities between 1 and 65 days after onset of symptoms were 94.4% and 78.7%, for IgG and IgM test, respectively. The sensitivity increased with the time after symptom onset, and rose to the top on the 22nd to 28th days. The total imprecision (CVs) was less than 6.0% for IgG and less than 6.5% for IgM. Limited cross-reactions with antibodies against EBV, CMV, mycoplasma pneumonia, human RSV, adenovirus, influenza A or influenza B were found. These data suggested the chemiluminescent SARS-CoV-2 IgG and IgM, assay with reliable utility and sensitivity, could be used for rapid screening and retrospective surveillance of COVID-19.

Comparison of the disinfecting effect of sodium hypochlorite aqueous solution and surfactant on hospital kitchen hygiene using adenosine triphosphate swab testing.

The Japanese Ministry of Health requires large-scale cooking facilities to use sodium hypochlorite aqueous solution (HYP) on food preparation tools, equipment, and facilities to prevent secondary contamination. This study aimed to compare the disinfecting effect of HYP and surfactant using adenosine triphosphate (ATP) swab testing on large-scale equipment and facilities that could not be disassembled and disinfected in hospital kitchen. From May 2018 to July 2018, ATP swab tests were performed on the following six locations in the Shizuoka Cancer Centre Dietary Department Kitchen: cooking counter, mobile cooking counter, refrigerator handle, conveyor belt, tap handle, and sink. Six relative light unit (RLU) measurements were taken from each location. The log10 values of the RLU measurements were evaluated by dividing the samples into two groups: the control group (surfactant followed by HYP swabbing) and the HYP group (HYP swabbing only). The results showed that the RLUs (log10 values) in both the groups improved after disinfection (p<0.05), except for the RLUs (log10 values) of the mobile cooking counter, tap handle, and sink in the control group after the HYP swab. The changes in the RLU (log10 value) did not differ between the two groups for all locations of the kitchen. Hence, HYP swabbing of large-scale equipment and facilities provides the same level of disinfection as surfactants and can be as beneficial.

Structure-based Design of a Specific, Homogeneous Luminescence Enzyme Reporter Assay for SARS-CoV-2.

Recombinant antibodies (Abs) against the SARS-CoV-2 virus hold promise for treatment of COVID-19 and high sensitivity and specific diagnostic assays. Here, we report engineering principles and realization of a Protein-fragment Complementation Assay (PCA) detector of SARS-CoV-2 antigen by coupling two Abs to complementary N- and C-terminal fragments of the reporter enzyme Gaussia luciferase (Gluc). Both Abs display comparably high affinities for distinct epitopes of viral Spike (S)-protein trimers. Gluc activity is reconstituted when the Abs are simultaneously bound to S-protein bringing the Ab-fused N- and C-terminal fragments close enough together (8 nm) to fold. We thus achieve high specificity both by requirement of simultaneous binding of the two Abs to the S-protein and also, in a steric configuration in which the two Gluc complementary fragments can fold and thus reconstitute catalytic activity. Gluc activity can also be reconstituted with virus-like particles that express surface S-protein with detectable signal over background within 5 min of incubation. Design principles presented here can be readily applied to develop reporters to virtually any protein with sufficient available structural details. Thus, our results present a general framework to develop reporter assays for COVID-19, and the strategy can be readily deployed in response to existing and future pathogenic threats and other diseases.

Performance of the rapid high-throughput automated electrochemiluminescence immunoassay targeting total antibodies to the SARS-CoV-2 spike protein receptor binding domain in comparison to the neutralization assay.

BACKGROUND: Neutralization tests (NT) are the gold standard for detecting and quantifying anti-SARS-CoV-2 neutralizing antibodies (NAb), but their complexity restricts them to research settings or reference laboratories. Antibodies against S protein receptor binding domain (RBD) have been shown to confer a neutralizing activity against SARS-CoV-2. Assays quantitatively measuring anti-S1-RBD-SARS-CoV-2 antibodies could be of great value for NAb screening of potential donors for convalescent-phase plasma therapy, assessing natural or vaccine-induced immunity, stratifying individuals for vaccine receipt, and documenting vaccine response. METHODS: Elecsys Anti-SARS-CoV-2 S (Elecsys-S), a high-throughput automated electrochemiluminescence double-antigen sandwich immunoassay for quantitative measurement of pan-anti-S1-RBD-SARS-CoV-2 antibodies, was evaluated against NT on 357 patients with PCR-confirmed SARS-CoV-2 infection. NT was performed in a BSL-3 laboratory using a Slovenian SARS-CoV-2 isolate; the NT titer ≥1:20 was considered positive. RESULTS: Elecsys-S detected pan-anti-S1-RBD-SARS-CoV-2 antibodies in 352/357 (98.6 %) samples. NAb were identified by NT in 257/357 (72 %) samples. The Elecsys-S/NT agreement was moderate (Cohen's kappa 0.56). High NT titer antibodies (≥1:160) were detected in 106/357 (30 %) samples. Elecsys-S's pan-anti-S1-RBD-SARS-CoV-2 antibody concentrations correlated with individual NT titer categories (the lowest concentrations were identified in NT-negative samples and the highest in samples with NT titer 1:1,280), and the Elecsys-S cutoff value for reasonable prediction of NAb generated after natural infection was established (133 BAU/mL). CONCLUSION: Although NT should remain the gold standard for assessing candidates for convalescent-phase plasma donors, selected commercial anti-SARS-CoV-2 assays with optimized cutoff, like Elecsys-S, could be used for rapid, automated, and large-scale screening of individuals with clinically relevant NAb levels as suitable donors.

Diagnostic accuracy comparison of three fully automated chemiluminescent immunoassay platforms for the detection of SARS-CoV-2 antibodies.

BACKGROUND: Serological test is an essential surveillance tool to track down the extensiveness of SARS-CoV-2 transmission and subsequently to move out from the enforced lockdown stage. OBJECTIVE: The study measures the diagnostic accuracy of three popular chemiluminescent immunoassay (CLIA) based automated platforms for the detection of anti-SARS-CoV-2 antibodies and compares their agreements. STUDY DESIGN: Serum samples of 594 COVID-19 positive patients and 100 samples from pre-COVID cases were tested by three CLIA based automated platforms: Abbott architect i2000SR, Roche cobas e411 and Yhlo iFlash 1800 and their diagnostic accuracy were compared by the area under the curves (AUC) value obtained from receiver operator characteristic (ROC) curves. Cohen's kappa statistic and McNemar's test were used to interpret the agreement between the platforms. RESULTS: All three platforms showed high specificity as claimed by the manufacturer. Sensitivity was calculated as 64.48 % (58.67-70.3) for Abbott, 80.48 % (76.62-84.34) for Roche and 76.94 % (72.65-81.23) for Yhlo. AUC was maximum for Roche (0.929). The Cohen's kappa value was determined in between 0.69-0.89 as the inter-rater agreements. CONCLUSION: The overall statistical analysis demonstrated cobas e411 as the diagnostically most accurate platform among the three.

Validation of a new automated chemiluminescent anti-SARS-CoV-2 IgM and IgG antibody assay system detecting both N and S proteins in Japan.

PCR methods are presently the standard for the diagnosis of Coronavirus disease 2019 (COVID-19), but additional methodologies are needed to complement PCR methods, which have some limitations. Here, we validated and investigated the usefulness of measuring serum antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using the iFlash3000 CLIA analyzer. We measured IgM and IgG titers against SARS-CoV-2 in sera collected from 26 PCR-positive COVID-19 patients, 53 COVID-19-suspected but PCR-negative patients, and 20 and 100 randomly selected non-COVID-19 patients who visited our hospital in 2020 and 2017, respectively. The repeatability and within-laboratory precision were obviously good in validations, following to the CLSI document EP15-A3. Linearity was also considered good between 0.6 AU/mL and 112.7 AU/mL for SARS-CoV-2 IgM and between 3.2 AU/mL and 55.3 AU/mL for SARS-CoV-2 IgG, while the linearity curves plateaued above the upper measurement range. We also confirmed that the seroconversion and no-antibody titers were over the cutoff values in all 100 serum samples collected in 2017. These results indicate that this measurement system successfully detects SARS-CoV-2 IgM/IgG. We observed four false-positive cases in the IgM assay and no false-positive cases in the IgG assay when 111 serum samples known to contain autoantibodies were evaluated. The concordance rates of the antibody test with the PCR test were 98.1% for SARS-CoV-2 IgM and 100% for IgG among PCR-negative cases and 30.8% for SARS-CoV-2 IgM and 73.1% for SARS-CoV-2 IgG among PCR-positive cases. In conclusion, the performance of this new automated method for detecting antibody against both N and S proteins of SARS-CoV-2 is sufficient for use in laboratory testing.