Tuning the composition of immiscible gold and nickel colloidal nanoalloys through plasmon induced laser mixing Gabriele C. Messina 1 *, Marco G. Sinatra 2 , Valentina Bonanni 3,4 , Rosaria Brescia 5 , Giulio Campo 3 , Francesco Pineider 3,6 , Claudio Sangregorio 7 , Giovanni Li-Destri 8 , Gianfranco Sfuncia 9 , Giovanni Marletta 9 , Alessandro Alabastri 10 , Remo Proietti Zaccaria 1 , Francesco De Angelis 1 , Giuseppe Compagnini 2 1 Plasmon Nanotechnologies, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy 2 Laboratory for Thin Films and Nanostructures (LABFSN), Department of Chemical Sciences, University of Catania, Viale Andrea Doria 6, 95124 Catania, Italy 3 Department of Chemistry, University of Florence & INSTM, Via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy 4 Department of Physics, University of Milan & CNR-IOM, Trieste, I-34149, Italy 5 Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy 6 Department of Chemistry and Industrial Chemistry, University of Pisa, Via Moruzzi 3, 56124 Pisa, Italy 7 ICCOM-CNR, Sesto Fiorentino, Florence, I-50019, Italy 8 European Synchrotron Radiation Facility, 71 Avenue des Martyrs, 38000 Grenoble, Francia 9 Laboratory for Molecular Surfaces and Nanotechnology (LAMSUN), Department of Chemical Sciences, University of Catania and CSGI, Viale Andrea Doria 6, 95124, Catania, Italy 10 Department of Physics and Astronomy MS 61, Laboratory for Nanophotonics, Smalley-Curl Institute, Rice University, Houston, TX 77005, USA *corresponding author: gabriele.messina@iit.it ABSTRACT We report the formation of Au x Ni 1-x alloy nanoparticles obtained by pulsed laser irradiation of Au and Ni@NiO colloidal mixtures. Structural and compositional characterization performed through X-Ray Diffraction and Transmission Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy has shown a correlation between the final alloy composition and the different Au/Ni@NiO ratio in the irradiated mixture.