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

• Published in: European journal of inorganic chemistry 2017-07, Vol.2017 (25), p.3205-3213
• Main Authors: Francis, Biju, Neuhaus, Bernhard, Reddy, M. L. P., Epple, Matthias, Janiak, Christoph
• Format: Article
• Language: English
• Subjects: Aminopropyltriethoxysilane; Biocompatibility; Biosensors; Carbazoles; Cell uptake; Covalence; Europium; Excitation; In vitro methods and tests; Inorganic chemistry; Ligands; Luminescence; Nanoparticles; Optical properties; Phosphine oxide; Silicon dioxide; Synthesis
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201700240

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 β‐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)‐10H‐phenoxazine (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. A visible‐light‐excitable, carbazole‐based Eu3+ complex, covalently incorporated into silica nanoparticles, has a luminescence quantum yield as high as 38 % and an excited‐state lifetime of up to 638 µs at physiological pH. Cell‐uptake studies with HeLa cells revealed that the nanoparticles enter the cells and are not cytotoxic.