Boosting SARS-CoV-2 Enrichment with Ultrasmall Immunomagnetic Beads Featuring Superior Magnetic Moment

The isolation and enrichment efficiencyof SARS-CoV-2virus incomplex biological environments is often relatively low, presentingchallenges in direct detection and an increased risk of false negatives,particularly during the early stages of infection. To address thisissue, we have developed a novel approach using ultrasmall magnetosome-likenanoparticles (& LE;10 nm) synthesized via biomimetic mineralizationof the Mms6 protein derived from magnetotactic bacteria. These nanoparticlesare surface-functionalized with hydrophilic carboxylated polyethyleneglycol (mPEG2000-COOH) to enhance water solubility and monodispersity.Subsequently, they are coupled with antibodies targeting the receptor-bindingdomain (RBD) of the virus. The resulting magnetosome-like immunomagneticbeads (Mal-IMBs) exhibit high magnetic responsiveness comparable tocommercial magnetic beads, with a saturation magnetization of 90.6emu/g. Moreover, their smaller particle size provides a significantadvantage by offering a higher specific surface area, allowing fora greater number of RBD single-chain fragment variable (RBD-scFv)antibodies to be coupled, thereby enhancing immune capture abilityand efficiency. To validate the practicality of Mal-IMBs, we evaluatedtheir performance in recognizing the RBD antigens, achieving a maximumcapture ability of 83 & mu;g/mg per unit mass. Furthermore, we demonstratedthe binding capability of Mal-IMBs to SARS-CoV-2 pseudovirus usingfluorescence microscopy. The Mal-IMBs effectively enriched the pseudovirusat a low copy concentration of 70 copies/mL. Overall, the small Mal-IMBexhibited excellent magnetic responsiveness and binding efficiency.By employing a multisite virus binding mechanism, it significantlyimproves the enrichment and separation of SARS-CoV-2 in complex environments,facilitating rapid detection of COVID-19 and contributing to effectivemeasures against its spread.