Optical sensing of titanium dioxide nanoparticles within horny layer of human skin and their protecting effect against solar UV radiation

In the present paper the problem of protection of human skin against harmful UV solar rays using nano-sized spherical particles of titanium dioxide and sensing their concentration if embedded into skin is considered. Experimental tape-stripping method was used to reveal the in-depth distribution of the particles within the horny layer up to 20 µm. Computer simulations of optical coherence tomography (OCT) investigations of skin and, in particular, horny layer in vitro with and without titanium dioxide particles added were also performed in order to understand, if this modern non-invasive technique is applicable for skin study and revealing the distribution of nanoparticles within the horny layer. The effect of particles size (25-200 nm) and concentration on simulated OCT signals was analyzed. The increase of scattering in the sample (with increase of particles concentration or size) leads to increase of the OCT signal slope and decrease of rear border peak. We also performed simulations implementing the Monte Carlo technique to evaluate the protecting effect of titanium dioxide nanoparticles of different size. The most effective sizes were revealed. Computations were performed for the wavelength of 290.5 nm as the most harmful one. Dependencies of light intensities absorbed, backscattered, and transmitted through the whole horny layer (20 µm thick) on concentration of titanium dioxide particles (0-5%) were obtained and analyzed.