Amine-Functionalized Silica Nanoparticles Incorporating Covalently Linked Visible-Light-Excitable Eu3+ Complexes: Synthesis, Characterization, and Cell-Uptake Studies

Abstract

We report the synthesis, characterization, photophysical investigations, and cell-uptake studies of luminescent silica nanoparticles incorporating covalently linked visible-light-excitable Eu3+ complexes. Visible-light excitation was accomplished by using highly conjugated carbazole-based -diketonate ligands. Covalent incorporation of the Eu3+ complexes into the silica nanoparticles was achieved by modification of the bidentate phosphine oxide 4,6-bis(diphenylphosphoryl)-10Hphenoxazine (DPOXPO), which was used as the neutral donor for the Eu3+ ion. The surface amine functionalization of the nanoparticles was carried out using aminopropyltriethoxysilane (APTES). The prepared nanoparticles (Eu@Si-OH and Eu@Si- NH2) are around 35–40 nm in diameter, monodisperse, stable in aqueous dispersion, and also retain the luminescent properties of the incorporated Eu3+ complex. The synthesized nanoparticles exhibit a promising luminescence quantum yield of 38 % and an excited-state lifetime of 638 μs at physiological pH. The photobleaching experiments revealed that the developed nanoparticles are more photostable than the parent Eu3+ complex 1. In vitro experiments with Eu@Si-NH2 nanoparticles on HeLa cells showed that they are biocompatible and are readily taken up by cells.