Nanocomposites and nanomaterials

The effect of laser irradiation on nanocomposites thermosensitive copolymer/gold nanoparticles/photosensitizer

Yu. Kuziv, V. Pavlov, N. Kutsevol, N. Davidenko

Taras Shevchenko National University of Kyiv, 62a Volodymyrska St., 01601 Kyiv, Ukraine;
E-mail: garaguts.yulia.fox@gmail.com.

Recently, it was shown the possibility of using nanocomposites based on thermosensitive polymers as targeted delivery systems of photosensitizers (PS) for photodynamic antitumor therapy (PDT). Nanocomposites are able to accumulate at the tumor site through the enhanced permeability and retention effect (EPR effect), which is the basis of passive targeting. Polymers also allow to prevent aggregation of PS molecules, which leads to a decrease in its activity. In addition, polymer-based nanocomposites can be further loaded with various drugs, which enhance the effect of the treatment. Gold nanoparticles have recently been proposed for use in PDT. In systems containing gold nanoparticles (AuNPs), it is possible to achieve an increase in the quantum yield of singlet oxygen formation. 
The method of holographic interferometry was used for the investigation of photothermal and photochemical reactions in nanocomposites. The laser was used with irr = 650 nm which is close to the long-wavelength maximum absorption of Au nanoparticles.
In our investigation a hybrid nanosystem containing a single branched polymer, gold nanoparticles and photosensitizer was synthesized and tested. As the polymer-nanocarrier was used star-like thermosensitive copolymer with the dextran core and poly(N-isopropylacrylamide) branches, and as a photosensitizer was used Chlorin e6. 
Poly(N-isopropylacrylamide) is water-soluble thermosensitive polymer. It undergoes hydrophilic to hydrophobic phase transition when temperature increases, exhibiting lower critical solution temperature (LCST) behaviour. Below the LCST, the polymer is soluble, but when temperature increases, it experiences a reversible volume phase transition.
It was shown that over time (tirr) after the illumination begins, the refractive index increases. 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.