Bacterial ligands as flexible and sensitive detectors in rapid tests for antibodies to SARS-CoV-2

Abstract

Lateral flow immunoassay (LFIA) is widely employed as point-of-care tests (POCT) for the diagnosis of infectious diseases. The accuracy of LFIA largely depends on the quality of the immunoreagents used. Typical LFIAs to reveal the immune response to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) employ anti-human immunoglobulin (hIG) antibodies and recombinant viral antigens, which usually are unstable and poorly soluble. Broad selective bacterial proteins, such as Staphylococcal protein A (SpA) and Streptococcal protein G (SpG) can be considered alternatives to anti-hIG to increase versatility and sensitivity of serological LFIAs because of their high binding capacity, interspecies reactivity, and robustness. We developed two colorimetric LFA devices including SpA and SpG linked to gold nanoparticles (GNP) as detectors and explored the use of a specific, stable, and soluble immunodominant fraction of the nucleocapsid protein from SARS-CoV-2 as the capturing agent. The optimal amount of SpA-GNP and SpG-GNP conjugates and the protein-to-GNP ratios were defined through a full factorial experimental design to maximize the diagnostic sensitivity of the LFIAs. The new LFA devices were applied to analyze 105 human serum samples (69 positive and 36 negatives according to reference molecular diagnostic methods). The results showed higher sensitivity (89.9%, 95% CI 82.7–97.0) and selectivity (91.7%, 82.6–100) for the SpA-based compared to the SpG-based LFA. In addition, 18 serum samples from cats and dogs living with COVID-19 patients were analyzed and 14 showed detectable levels of anti-SARS-CoV-2 antibodies, thus illustrating the flexibility of the SpA- and SpG-based LFAs. Graphical abstract

Investigation of the “Antigen Hook Effect” in Lateral Flow Sandwich Immunoassay: The Case of Lumpy Skin Disease Virus Detection

“…The following supporting information can be downloaded at: . Chemicals, AuNP synthesis, flocculation test [ 32 ]. Figure S1: Flocculation stress test for the mAb #2C6 (a) and for the mAb #2F10 (b).…”

Point-of-care electrochemical testing of biomarkers involved in inflammatory and inflammatory-associated medical conditions

“…The fast (30 min) and sensitive detection of SARS-CoV-2 antibodies was recorded with a LOD of 1 ng/mL that enabled the application of the sensor only in serum samples as for human nasopharyngeal swabs the values of IgG and IgM go down to pg/mL [ 144 ]. Unlike lateral flow immunoassay (LFA) platforms where multiple antibodies are exploited in charge of the reporter, no antibodies are required if label-free electrochemical systems are applied [ 150 ]. Although sensitive and cost-effective, ePADs fail to accurately and uniformly control the flow rate that dramatically influences the performance of the sensor.…”

“…Among these, we mention the high sensitivity ensured by the easy functionalization with nanomaterials, the high selectivity when using biological or biomimetic elements, the fast response, but especially their suitability for miniaturization and automation, basic properties in the field of POCT sensing devices. It can be observed that only one example of detection devices does not meet the criteria “Specific” [ 36 ], respectively, “Sensitive” [ 150 ], which can be a justification for the large number of recent studies that include electrochemical sensors and biosensors aimed at the development of POCT devices for biomedical and clinical practice, where real, biological samples are very complex in composition and usually contain very low concentrations of analytes.…”

“…It can be observed that only one example of detection devices does not meet the criteria “Specific” [ 36 ], respectively, “Sensitive” [ 150 ], which can be a justification for the large number of recent studies that include electrochemical sensors and biosensors aimed at the development of POCT devices for biomedical and clinical practice, where real, biological samples are very complex in composition and usually contain very low concentrations of analytes.…”

Silent Antibodies Start Talking: Enhanced Lateral Flow Serodiagnosis with Two-Stage Incorporation of Labels into Immune Complexes

“…Serodiagnosis is typically implemented using immunoglobulin-binding proteins, such as anti-species antibodies or bacterial protecting compounds (staphylococcal protein A, streptococcal protein G, etc.) [ 16 ]. In the common LFIA format, they are immobilized on colored nanoparticles, applied on a test strip, and form complexes with all immunoglobulins, including those specific to the target pathogen during lateral flow.…”