Increasing the efficiency of lanthanide luminescent bioprobes: bioconjugated silica nanoparticles as markers for cancerous cellsElectronic supplementary information (ESI) available: Description of synthesis of nanoparticle bioconjugates with avidin, comparison between luminescence spectra of un-doped SiO2/NH2 and doped with [Eu2(LC2)3] nanoparticles (Fig. S1), and immunoluminescent detection of 5D10 Ag on MCF-7 cells by 5D10 with the NP-IgG probe (Fig. S2). See DOI: 10.1039/c0nj00440e

The lanthanide binuclear helicate [Ln 2 (L C2 ) 3 ] has been embedded into bare and NH 2 -functionalized silica nanoparticles (NPs) using water-in-oil microemulsion technique. TEM analysis reveals both [Ln 2 (L C2 ) 3 ]@SiO 2 and [Ln 2 (L C2 ) 3 ]@SiO 2 /NH 2 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 ([Gd 2 (L C2 ) 3 ]@NP), does not change upon incorporation into silica nanoparticles and is optimal for sensitizing Eu III luminescence. As a consequence, [Eu 2 (L C2 ) 3 ]@SiO 2 and [Eu 2 (L C2 ) 3 ]@SiO 2 /NH 2 NPs display red emission due to characteristic 5 D 0 → 7 F J ( J = 0-4) transitions with absolute quantum yield reaching 28% for the latter. NH 2 -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 [Eu 2 (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. Lanthanide binuclear helical luminescent bioprobes are introduced into IgG conjugated silica nanoparticles and used to detect the 5D10 antigen expressed by breast cancer MCF-7 cells via a time-resolved immunoluminescent assay.