Nanocomposites and nanomaterials

Anomalous change of refractive index for Au sols under laser illumination
Yu. Harahuts, V. Pavlov, E. Mokrinskaya, I. Davidenko, N. Davidenko, N. Kutsevol
Taras Shevchenko National University of Kyiv, Volodymyrska st., 60, 010601 Kyiv, Ukraine
E-mail: garaguts.yulia.fox@gmail.com
The comparative refractive index analysis for two systems: Au sol synthesized into solution of Dextran-graft-Polyacrylamide (D-g-PAA) star-like copolymer and solution of D-g-PAA under laser illumination has been carried out. The polymer molecular characteristics were described in [1]. It was established that Au nanoparticles (AuNPs) have 1.5 – 6 nm in size. The size of individual polymer molecule in solution was equal to 50–60 nm. Au/D-g-PAA nanosystem was successfully used as nanocarrier for photodynamic anticancer therapy [2].
To understand the effect of laser illumination to composite nanoscale systems, the method of holographic interferometry in real time was proposed and experimentally applied. The method is tested using the equipment kit [3] to determine the refractive index (n) and its change (n) of liquid and gaseous media. The necessity of such research is determined by the problems existing in practical medicine [4]. Photographs of cuvettes with this solution are presented as the example after the hologram registration and further in the process of illumination with laser light.

tirr = 2 s      tirr = 4 s       tirr = 11 s     tirr = 15 s
It is evident that over time (tirr) after the illumination begins, the number of interference bands increases testifying an increase of n. After ceasing the light, the interference pattern relaxes and the bands disappear. The interference bands are localized only in the volume limited by the laser beam and there is no observed diffusion of the heated solution into other parts of the cuvette.
Acknowledgements. This publication is supported in part by the grant of the State Fund For Fundamental Research (Ukraine), project Ф76/64-2017 “New multifunctional hybrid nanocomposites for photodynamic chemotherapy of tumor cells” and by the grant of the Department of Targeted Training of Taras Shevchenko National University of Kyiv at National Academy of Sciences of Ukraine, project 28Ф “Physical mechanisms of the oxygen molecules excitation in functional nanosystems for medical application”
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2.	N. Kutsevol et al. Applied Nanoscience.-2018. - In Press.
3.	N. Davidenko et al. Appl. Optics.-2018.-57 (8).-P. 1832-1837.
4.	N. Davidenko et al. Proc. SPIE.-2018.-10612.-P. 106120H.