A Newly Identified Spike Protein Targeted Linear B-Cell Epitope Based Dissolvable Microneedle Array Successfully Eliciting Neutralizing Activities against SARS-CoV-2 Wild-Type Strain in Mice.

Vaccination is a cost-effective medical intervention. Inactivated whole virusor large protein fragments-based severe acute respiratory syndrome coronavirus (SARS-CoV-2) vaccines have high unnecessary antigenic load to induce allergenicity and/orreactogenicity, which can be avoided by peptide vaccines of short peptide fragments that may induce highly targeted immune response. However, epitope identification and peptide delivery remain the major obstacles in developing peptide vaccines. Here, a multi-source data integrated linear B-cell epitope screening strategy is presented and a linear B-cell epitope enriched hotspot region is identified in Spike protein, from which a monomeric peptide vaccine (Epitope25) is developed and applied to subcutaneously immunize wildtype BALB/c mice. Indirect ELISA assay reveals specific and dose-dependent binding between Epitope25 and serum IgG antibodies from immunized mice. The neutralizing activity of sera from vaccinated mice is validated by pseudo and live SARS-CoV-2 wild-type strain neutralization assays. Then a dissolvable microneedle array (DMNA) is developed to pain-freely deliver Epitope25. Compared with intramuscular injection, DMNA and subcutaneous injection elicit neutralizing activities against SARS-CoV-2 wild-type strain as demonstrated by live SARS-CoV-2 virus neutralization assay. No obvious damages are found in major organs of immunized mice. This study may lay the foundation for developing linear B-cell epitope-based vaccines against SARS-CoV-2.

A copper ion-mediated on-off-on gold nanocluster for pyrophosphate sensing and bioimaging in cells.

Herein, gold nanoclusters (AuNCs@EW@Lzm, AuEL) with the bright red fluorescence at 650 nm were prepared by egg white and lysozyme as double protein ligands, which exhibited good stability and high biocompatibility. The probe displayed highly selective detected pyrophosphate (PPi) based on Cu2+-mediated AuEL fluorescence quenching. Specifically, the fluorescence of AuEL was quenched once the Cu2+/Fe3+/Hg2+ is added to chelate with amino acids on the AuEL surface, respectively. Interestingly, the fluorescence of quenched AuEL-Cu2+ was significantly recovered by PPi, but not the other two. This phenomenon was attributed to the stronger bond between PPi and Cu2+ than that of Cu2+ with AuEL nanoclusters. The results demonstrated a good linear relationship between PPi concentration and the relative fluorescence intensity of AuEL-Cu2+ in the range of 131.00-685.40 µM with a detection limit of 2.56 µM. In addition, the quench AuEL-Cu2+ system can also be recovered in acidic environments (pH ≤ 5). And the as-synthesized AuEL showed excellent cell imaging and target the nucleus. Thus the fabrication of AuEL offers a facile strategy for efficient PPi assay and offers the potential for drug/gene delivery to the nucleus.

Lysozyme-encapsulated gold nanoclusters for ultrasensitive detection of folic acid and in vivo imaging.

Herein, lysozyme-encapsulated gold nanoclusters (AuNCs@Lzm, AuL) were favorably obtained by a simple and economical synthesis. The resulting AuL exhibits low toxicity, exceptional stability and intense red fluorescence at 650 nm, which can enter living cells and is mainly located in lysosomes. The AuL selectively and sensitively drove to detect folic acid (FA) with a detection limit as low as 0.19 nM based on the combination of the static quenching and the internal filtering effect. Interestingly, the fascinating results discovered that the AuL with ignorable toxicity was adsorbed from the intestine into the liver, and essentially was cleared from the body in 6 days without significant bioaccumulation in zebrafish. Furthermore, the hyaluronic acid (HA) coating AuLH exhibits remarkably targeted tumors towards MCF-7>HeLa > HepG2¼NIH/3T3≈DC, which attributed to the number of receptors expressed by the cells. All these advantages highlight that the AuL is a versatile nanoplatform for sensing, in vivo fluorescence imaging and tumor targeting.