Fluorescent hybrid organic–inorganic particles: influence of physical encapsulation versus covalent attachment on leaching and UV stability

Hybrid organic–inorganic materials provide the opportunity for combining organic chromophores into inorganic networks. The resulting hybrids can be used for numerous optical, biomedical and nanotechnology applications. Hybrid organic–inorganic particles that absorb and fluoresce in visible or ultraviolet light are particularly useful for bio-imaging, sensors, and as a safe sun-screen. The organic component can be incorporated through physical entrapment or through covalent incorporation through siloxane linkages. By containment in the hybrid material, the performance lifetime of the chromophore can be extended significantly and environmental contamination by its leaching out can be reduced. In this study, silica particles containing 1 mol % dimethylaminonathyl-sulfonamide (dansyl) dyes were prepared by three different methods: 1) physical encapsulation inside a hollow silica particle, 2) covalent attachment of pendant chromophores through a single silyl group and 3) covalent attachment through two silyl groups. The influence of the mode of entrapment on the particles’ spectroscopic properties, the propensity of the chromophores to leach from the particles, and photochemical degradation of chromophores were determined for the three classes of hybrid materials.