1 DOI: 10.1002/((please add manuscript number)) Article type: Communication Photothermally Responsive Inks For Inkjet-Printing Secure Information Giuseppe Chirico, Giacomo Dacarro, Colm O'Regan, Jouko Peltonen, Jawad Sarfraz, Angelo Taglietti, Mykola Borzenkov, * and Piersandro Pallavicini * Dr. M. Borzenkov Dipartimento di Medicina e Chirurgia and Nanomedicine Center, Università di Milano-Bicocca, piazza dell’Ateneo Nuovo, 20126, Milano, Italy; Prof. G. Chirico Dipartimento di Fisica and Nanomedicine Center, Università di Milano-Bicocca, piazza dell’Ateneo Nuovo, 20126, Milano, Italy; CNR - ISASI, Institute of Applied Sciences & Intelligent Systems, Via Campi Flegrei 34, Pozzuoli, NA, Italy E-mail: mykola.borzenkov@unimib.it Prof. G. Dacarro, A. Taglietti, P. Pallavicini Dipartimento di Chimica, Università di Pavia, viale Taramelli, 12, 27100 Pavia, Italy E-mail: piersandro.pallavicini@unipv.it Dr. Colm O’Regan King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering (BESE) Division, NABLA Lab, 23955-5900 Thuwal, Saudi Arabia Dr. J. Peltonen Laboratory of Physical Chemistry, Center for Functional Materials, Åbo Akademi University, Porthaninkatu 3-5, 20500, Turku, Finland Dr. J. Sarfraz, Nofima—Norwegian Institute of Food, Fisheries and Aquaculture Research, P.O. Box 210, NO- 1431 Ås, Norway and Laboratory of Physical Chemistry, Center for Functional Materials, Åbo Akademi University, Porthaninkatu 3-5, 20500, Turku, Finland Keywords: nanoinks, gold nanostars, secure information, inkjet printing, photothermal effect Abstract. 2D patterns of photothermally responsive Near-Infrared (NIR) absorbing gold nanostars (GNS), coated with multiple charged polymer layers, have been inkjet-printed on a glass surface. The shape of the LSPR NIR absorption bands in the printed patterns looses its peaked form due to plasmon coupling, unless GNS are enveloped in multiple coating layers, keeping the inter-GNS distance sufficiently large. In the latter case, the photo-thermal temperature increase (T) induced by the NIR laser irradiation follows a T vs irradiation wavelength (irr) profile with the same sharply peaked shape of the LSPR bands of the liquid ink. With this result, a new paradigm for inkjet-writing secure information is introduced, as an alternative to the current methods based on direct visual inspection of printed patterns. While the