Synthesis of stable carboxy-terminated NaYF4: Yb3+, Er3+@SiO2 nanoparticles with ultrathin shell for biolabeling applications

Abstract

Here, a two-step method has been developed for synthesizing carboxy-terminated NaYF₄: Yb³⁺, Er³⁺@SiO₂ core@shell nanoparticles (UCNP@SiO₂) with ultrathin shell (1.5 nm). First, the NaYF₄: Yb³⁺, Er³⁺ upconverting nanoparticles (UCNPs) were prepared using solvothermal technology; then, silica shells (SiO₂) were deposited on the nanocrystals to form core–shell structures by the hydrolysis of tetraethylorthosilicate (TEOS). The ultrathin SiO₂ shell was obtained by increasing surfactant amount and decreasing TEOS amount in the reaction mixture. Carboxyethylsilanetriol (CTES) was used to generate the carboxy group on the particle surface. The carboxy-terminated UCNP@SiO₂ are ideally suited for biolabeling and bioimaging applications because the as-prepared nanoparticles have extreme colloidal and optical stabilities, and the carboxy groups on the particle surface easily react with amino residues of biomolecules. As an example, we reported on the interactions of Ricinus Communis Agglutinin (RCA 120) conjugated UCNP@SiO₂ with HeLa cells. The excellent performance of the RCA 120 conjugated UCNP@SiO₂ in cellular fluorescence imaging was demonstrated.