RESEARCH PAPER Photoluminescent properties of spider silk coated with Eu-doped nanoceria Svetlana Dmitrović & Marko G. Nikolić & Branislav Jelenković & Marija Prekajski & Mihailo Rabasović & Aleksandra Zarubica & Goran Branković & Branko Matović Received: 28 June 2016 /Accepted: 23 January 2017 # Springer Science+Business Media Dordrecht 2017 Abstract Spider dragline silk was coated with pure as well as Eu-doped ceria nanopowders at the room tem- perature. The treatment was done by immersion of the spider silk mesh into aqueous solutions of cerium nitrate (Ce(NO 3 ) 3 ) and ammonium hydroxide (NH 4 OH). De- pending on the relationship between Ce 3+ ion and am- monium hydroxide concentration, coated fibers exhibit- ed a different thickness. Obtained materials were studied by means of FESEM. It was found that ceria nanoparti- cles of average size of 3 nm were coated along spider thread. X-ray diffraction (XRD) and selected-area elec- tron diffraction (SAED) confirmed crystal nature of nanoparticle coating of spider silk. By using Williamson-Hall plots, crystallite size and strain were estimated. EDS measurement confirmed the presence of Eu in spider-Eu-doped ceria composite, and according to FTIR analysis, the interaction between CeO2 and spider silk was proposed. The morphology of obtained composite was observed by TEM. The photoluminescence emission spectra of spider silk coat- ed with Eu-doped ceria were measured with two differ- ent excitations of 385 and 466 nm. The two-photon excited auto-fluorescence of spider silk coated with Eu-doped ceria was detected using a nonlinear laser scanning microscope. Obtained composite has a poten- tial as a fluorescent labeling material in diverse applications. Keywords Spider silk . Nanoceria . Europium . Coating . Photoluminescence . Nanoparticles Introduction Spider silk is a protein fiber spun by spiders and it can be used in various applications. Spiders can produce up to seven different types of fibers (Sponner et al. 2007). Among them, the dragline silk, that is produced in the major ampullate gland, is the most studied because of its high strength, stiffness, and toughness, joined with mod- erated elasticity, e.g., the strength of dragline silk of European garden spider Araneus diadematus spider is comparable to high-tech materials made by man (e.g., nylon, Kevlar, high tensile steel…), and silk produced by the major ampullate gland of spiders is among the stiffest and strongest polymeric biomaterials known (Gosline et al. 1999). Biocompatibility of spider silk is rather satisfying—it showed low local tolerance re- sponse and does not evoke strong immunological J Nanopart Res (2017) 19:47 DOI 10.1007/s11051-017-3750-9 S. Dmitrović (*) : M. Prekajski : B. Matović Vinča Institute of Nuclear Sciences, University of Belgrade, P. O. Box 522, Belgrade 11000, Serbia e-mail: svetlana8@vin.bg.ac.rs M. G. Nikolić : B. Jelenković : M. Rabasović Institute of Physics, University of Belgrade, Pregrevica 118, 11080, Zemun, Belgrade 11000, Serbia A. Zarubica Department of Chemistry, Faculty of Science and Mathematics, University of Niš, Višegradska 33, Niš 18000, Serbia G. Branković Institute for Multidisciplinary Research, Department of Material Science, University of Belgrade, Kneza Višeslava 1, Belgrade 11000, Serbia