Ultrastable Silver Nanoparticles for Rapid Serology Detection of Anti-SARS-CoV-2 Immunoglobulins G

Abstract

Dipstick assays using silver nanoparticles (AgNPs) stabilized by a thin calix[4]arene-based coating were developed and used for the detection of Anti-SARS-CoV-2 IgG in clinical samples. The calixarene-based coating enabled the covalent bioconjugation of the SARS-CoV-2 Spike Protein via the classical EDC/sulfo-NHS procedure. It further conferred remarkable stability to the resulting bioconjugated AgNPs, as no degradation was observed over several months. In comparison with lateral-flow immunoassays (LFIAs) based on classical gold nanoparticles, our AgNP-based system constitutes a clear step forward, as the limit of detection for Anti-SARS-CoV-2 IgG was reduced by 1 order of magnitude and similar signals were observed with 10 times fewer particles. In real clinical samples, the AgNP-based dipstick assays showed impressive results: 100% specificity was observed for negative samples, while a sensitivity of 73% was determined for positive samples. These values match the typical sensitivities obtained for reported LFIAs based on gold nanoparticles. These results (i) represent one of the first examples of the use of AgNP-based dipstick assays in the case of real clinical samples, (ii) demonstrate that ultrastable calixarene-coated AgNPs could advantageously replace AuNPs in LFIAs, and thus (iii) open new perspectives in the field of rapid diagnostic tests.

Ultra-stable silver nanoplates: efficient and versatile colorimetric reporters for dipstick assays

“…21,25–27 Very recently, we have shown that calixarene-coated AgNPs could advantageously replace gold nanoparticles of the same size ( i.e. around 20 nm) in a serological dipstick assay for the detection of Anti-SARS-CoV-2 Immunoglobulin G. 22 An improvement by one order of magnitude of the limit of detection was indeed obtained compared to AuNPs due to the better optical properties of silver. However, due to a lack of contrast with the white strip, the yellow band generated at the test line by the 20 nm AgNPs was difficult to observe with the naked eye.…”

“…17,18 In this context, we have recently reported the synthesis of ultra-stable Ag or AuNPs 19 and their use as colorimetric reporter in biosensing applications. [20][21][22] For this, the nanoparticles were stabilized with an ultra-thin calixarene-based layer obtained from the reductive grafting of calixarene-tetradiazonium salts. 23,24 Up to four bonds per calixarene can be formed with the surface, leading to a strongly anchored organic layer that provides extreme resistance to the nanomaterial and enables its conjugation with biomolecules.…”

Di-Arginine Additives for Dissociation of Gold Nanoparticle Aggregates: A Matrix-Insensitive Approach with Applications in Protease Detection

“…Noble nanomaterials and particularly gold nanoparticles (AuNPs) have emerged as remarkable colorimetric reporters due to their plasmonic properties. − AuNPs possess a localized surface plasmon resonance (LSPR) band in the visible region that is modulated by their size, shape, and dielectric environment. − Citrate-capped AuNPs (AuNPs–citrate) are the most common, convenient, and cost-effective form of gold colloids, and their synthesis via the Turkevich method is well established in the literature . AuNPs have been extensively studied, and various AuNP-based colorimetric sensors have been developed. − …”

Gold–Silver Core–Shell Nanoparticle Crosslinking Mediated by Protease Activity for Colorimetric Enzyme Detection

“…Spherical gold nanoparticles (AuNPs) are typically employed for colorimetric assays even though spherical silver nanoparticles (AgNPs) have an extinction coefficient that is one order of magnitude higher. , Therefore, plasmonic colorimetric biosensors that use AgNPs instead of AuNPs should result in lower limits of detection (LOD) . The reason for this discrepancy in adoption is because AuNPs have a superior colloidal stability in biological fluids and under oxidative conditions. , Although AgNPs are disadvantageous for applications where stability is of utmost importance, some groups have leveraged this instability by creating sensors that measure the optical change of pristine and degraded AgNPs in response to a target analyte. − …”