Preparation and time-gated luminescence bioimaging applications of long wavelength-excited silica-encapsulated europium nanoparticles

Silica-encapsulated luminescent lanthanide nanoparticles have shown great potential as biolabels for various time-gated luminescence bio-detections in recent years. The main problem of these nano-biolabels is their short excitation wavelengths within the UV region. In this work, a new type of silica-encapsulated luminescent europium nanoparticle, with a wide excitation range from UV to visible light in aqueous solutions, has been prepared using a conjugate of (3-isocyanatopropyl)triethoxysilane bound to a visible light-excited Eu3+ complex, 2,6-bis(1′,1′,1′,2′,2′,3′,3′-heptafluoro-4′,6′-hexanedion-6′-yl)-dibenzothiophene–Eu3+-2-(N,N-diethylanilin-4-yl)-4,6-bis(pyrazol-1-yl)-1,3,5-triazine (IPTES–BHHD–Eu3+–BPT conjugate), as a functionalized precursor. The nanoparticles, which are prepared by the copolymerization of the IPTES–BHHD–Eu3+–BPT conjugate, tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane in a water-in-oil reverse microemulsion consisting of Triton X-100, n-octanol, cyclohexane and water in the presence of aqueous ammonia, are monodisperse, spherical and uniform in size. Their diameter is 42 ± 3 nm and they are strongly luminescent with a wide excitation range from UV to ∼475 nm and a long luminescence lifetime of 346 μs. The nanoparticles were successfully used for streptavidin labeling and the time-gated luminescence imaging detection of two environmental pathogens, cryptosporidium muris and cryptosporidium parvium, in water samples. The results demonstrated the practical utility of the new nanoparticles as visible light-excited biolabels for time-gated luminescence bioassay applications.