RESEARCH PAPER High-yield aqueous synthesis of multi-branched iron oxide core–gold shell nanoparticles: SERS substrate for immobilization and magnetic separation of bacteria Ugur Tamer • Aykut Onay • Hakan Ciftci • Akif Go ¨ktug ˘ Bozkurt • Demet Cetin • Zekiye Suludere • I ˙ smail Hakkı Boyacı • Philippe Daniel • Fabienne Lagarde • Nader Yaacoub • Jean-Marc Greneche Received: 14 May 2014 / Accepted: 22 August 2014 Ó Springer Science+Business Media Dordrecht 2014 Abstract The high product yield of multi-branched core–shell Fe 3-x O 4 @Au magnetic nanoparticles was synthesized used as magnetic separation platform and surface-enhanced Raman scattering (SERS) sub- strates. The multi-branched magnetic nanoparticles were prepared by a seed-mediated growth approach using magnetic gold nanospheres as the seeds and subsequent reduction of metal salt with ascorbic acid in the presence of a stabilizing agent chitosan biopolymer and silver ions. The anisotropic growth of nanoparticles was observed in the presence of chitosan polymer matrix resulting in multi-branched nanoparticles with a diameter over 100 nm, and silver ions also play a crucial role on the growth of multi- branched nanoparticles. We propose the mechanism of the formation of multi-branched nanoparticles while the properties of nanoparticles embedded in chitosan matrix are discussed. The surface morphology of nanoparticles was characterized with transmission electron microscopy, scanning electron microscopy, ultraviolet visible spectroscopy (UV–Vis), X-ray diffraction, and fourier transform infrared spectros- copy and 57 Fe Mo ¨ssbauer spectrometry. Additionally, the magnetic properties of the nanoparticles were also examined. We also demonstrated that the synthesized Fe 3-x O 4 @Au multi-branched nanoparticle is capable of targeted separation of pathogens from matrix and sensing as SERS substrates. Electronic supplementary material The online version of this article (doi:10.1007/s11051-014-2624-7) contains supple- mentary material, which is available to authorized users. U. Tamer (&)  A. Onay Department of Analytical Chemistry, Faculty of Pharmacy, Gazi University, 06330 Ankara, Turkey e-mail: utamer@gazi.edu.tr H. Ciftci Department of Chemistry and Chemical Processing Technologies, Kırıkkale Vocational High School, Kırıkkale University, Yahs ¸ihan, 71450 Kırıkkale, Turkey A. G. Bozkurt Department of Food Engineering, Faculty of Engineering, Hacettepe University, Beytepe, 06800 Ankara, Turkey D. Cetin Science Teaching Programme, Gazi Faculty of Education, Gazi University, 06500 Ankara, Turkey Z. Suludere Department of Biology, Faculty of Science, Gazi University, 06500 Ankara, Turkey I ˙ . Hakkı Boyacı Department of Food Engineering, Faculty of Engineering and Food Research Center, Hacettepe University, Beytepe, 06800 Ankara, Turkey P. Daniel  F. Lagarde  N. Yaacoub  J.-M. Greneche Institut des Mole ´cules et des Mate ´riaux du Mans – IMMM – UMR CNRS 6283, Universite ´ du Maine, Av. O. Messiaen, 72085 Le Mans Cedex 9, France 123 J Nanopart Res (2014) 16:2624 DOI 10.1007/s11051-014-2624-7