Increasing the efficiency of lanthanide luminescent bioprobes: bioconjugated silica nanoparticles as markers for cancerous cells

Abstract

The lanthanide binuclear helicate [Ln₂(L^C2)₃] has been embedded into bare and NH₂-functionalized silica nanoparticles (NPs) using water-in-oil microemulsion technique. TEM analysis reveals both [Ln₂(L^C2)₃]@SiO₂ and [Ln₂(L^C2)₃]@SiO₂/NH₂ nanoparticles having a spherical morphology and being monodispersed with an average size of 55 ± 5 and 90 ± 10 nm, respectively. The energy of the ligand triplet state, ∼21 800 cm⁻¹ ([Gd₂(L^C2)₃]@NP), does not change upon incorporation into silica nanoparticles and is optimal for sensitizing Eu^III luminescence. As a consequence, [Eu₂(L^C2)₃]@SiO₂ and [Eu₂(L^C2)₃]@SiO₂/NH₂ NPs display red emission due to characteristic ⁵D₀ → ⁷F_J (J = 0–4) transitions with absolute quantum yield reaching 28% for the latter. NH₂-functionalized NPs have then been conjugated with avidin (NP-avidin) or goat anti-mouse IgG antibody (NP-IgG) to test them as luminescent biomarkers. Time-resolved microscopy of immunocytochemical assays involving recognition of mucin-like proteins expressed on breast cancer MCF-7 cells by the 5D10 monoclonal antibody confirms that the NP-IgG bioprobe displays specific luminescent signal with signal-to-noise ratio ≈20% higher than the one obtained for the bioconjugate of molecular [Eu₂(L^C2(COOH))₃] with IgG. In addition, immunoassays using a streptavidin-coated plate and the NP-IgG probe are able to detect 15 ng mL⁻¹ of the biotinylated 5D10 antibody with a signal-to-noise ratio of 100.