Unraveling the nature of NIR resonant nanoparticles

R. C. SALVAREZZA; M. S. MORENO; 1, C. VERICAT; C. M. MAIER; L. GIOVANETTI; F. G. REQUEJO; M. A. HUERGO

Campinas

Congreso; LNLS 27th Annual Users' Meeting (RAU); 2017

CNPEM

The selection of ideal materials for biomedical applications requires certain conditions not always easy to combine. Ideally, it is needed a nontoxic material, that could be reutilized to diminish doses to a minimum, with an adequate size for cell and tissues interaction and of course, that is efficient to remove malignant cells. Gold is an inert material that does not damage tissues itself due it does not chemically interact with them. This property makes it also very stable in an oxidative ambient, such as the biological medium. On the other hand, it is relatively easy to manipulate gold in the nanoscale, making it possible to grow nanostructures in the appropriate size to interact with cells and its components, that is neither too big, because it would not reach several locations, nor too small to become dangerous[1]. This malleability of gold allows scientists to synthetize nanoparticles (NP) with localized surface plasmon resonances (LSPR) in different positions of electromagnetic spectrum. In the last years, much effort has been done to improve the synthesis of gold nanoprisms because of the obvious advantages related to size and the energy of its LSPR in the NIR. One most popular strategy to synthetize gold nanoprisms is the use of sulfur compounds as reducing agents of the Au(III) ions. Sulfide and thiosulfate have been alternatively used to yield truncated gold nanoprims with excellent NIR absorption but also to a collection of non-active NIR spherical nanoparticles [3]. In particular the thiosulfate synthetic route has attracted great interest due to the large yield of nanoprims in relation to spherical particles. In this work we show preliminary results of the analysis of physical and chemical properties of Au NS resulting from the Au (III) reaction with thiosulfate ions. Our results shown that these NP are comparable in optical properties and bulk composition to those produced by the sulfide reaction, although with a better yield and easier control. Our data reveal that the thiosulfate synthesis proceeds by the same chemical route than that observed for the sulfide synthesis discarding the widely accepted route of thiosulfate oxidation to sulfate. XANES at the sulfur K edge reveals that the Thiosulfate decomposition to sulfide and the oxidation of these species to sulfur results in gold NP covered by a mixture of strongly adsorbed reduced sulfur species, similarly to those found when sulfide ions are used as reducing agents. The presence of Au0 in the nanostructure bulk was confirmed by EXAFS signal at the Au L edge. The presence of these species on the 3 nanostructure surface is crucial to understand and improve their biocompatibility, in particular when surface modification is made by the ligand exchange method [4].[1] Chithrani, D. B. Insciences J. 1, 115?135 (2011).[2] Chithrani, B. D., Ghazani, A. A. & Chan, W. C. W. Nano Lett. 6, 662?668 (2006).[3] Saverot, S.-E., Reese, L. M., Cimini, D., Vikesland, P. J. & Bickford, L. R. Nanoscale Research Letters 10, 241 (2015). [4] Charchar, P., Christofferson, A. J., Todorova, N. & Yarovsky, I. Small 12, 2395?2418 (2016).