Synthesis and characterization of monodisperse Eu-doped luminescent silica nanospheres for biological applications

Luminescent nanoparticles are gaining more and more interest for bio-sensing and bio-imaging applications. In particular it is desiderable to work with cheap and non toxic materials which could be easily functionalized in their surface. To these respects silica nanoparticles seem to be a very promising and interesting solution. The liquid synthesis of silica spheres can be obtained by condensation of tetraethylortosilicate (TEOS) in basic or acid environment. Several strategies have been developed to make them luminescent by the incorporation of organic or inorganic emission centres, but often requiring multiple processing steps and use of expensive or toxic molecules. Moreover, common dyes suffer disadvantages such as a broad spectral band, short fluorescent lifetime and photobleaching. In contrast, rare earths exhibit narrow emission bands, large Stokes shifts and long luminescence lifetimes. In this work we focus our attention on the synthesis and characterization of europium-doped silica spheres. Europium introduction in the spheres can be interesting for biological applications to increase the signal to noise ratio due to the long luminescence lifetime (possibility to perform time-delayed analysis) and to the good emission intensity. The obtained results are presented and discussed, giving suggestions for the optimization of their morphological and optical properties. The possibility of realizing good luminescent silica spheres by following the described procedure is shown and suggestions for future development are given. The cheap and easy synthesis of these luminescent particles, the stability in water, the easy surface functionalization and bio-compatibility makes them very attractive in biological imaging and other applications.