Significant UV Emission Absorption by Silicon in Upconversion Nanoparticles

Nanocontainers based on silicon nanostructures (SiNSs) have a number of undeniable advantages over other inorganic nanostructures used for drug delivery. The main advantage is their proven high biocompatibility as well as biodegradability. Due to the ease of modification of SiNSs, specific delivery of various hydrophobic and hydrophilic drugs to cells within the required time frame can be achieved. Due to the presence of red PL, SiNSs can also be used as contrast agents for multimodal bioimaging. Our group has reported in previous studies multimodal bioimaging using Raman spectroscopy of SiNSs nanocontainers without and with doxorubicin loading [1-3]. The main scientific goal of this work is to combine silicon-based nanostructures and upconversion nanoparticles (UCNPs) and improve the possible energy transfer between SiNSs and NaYF4 upconversion nanoparticles doped with thulium (Tm³⁺) with strong UV-blue emission as a possible drug delivery or targeting system for theranostics applications in nanomedicine. To realize the effective interaction between both nanostructures, a novel in situ synthesis strategy was developed and investigated (TEM, UV-vis, emission), in which silicon nanoparticles were added as a nucleation center in the solution to grow UCNPs. Our results clearly show that more than 97% of the UV-blue emission of UCNPs is absorbed by SiNSs, which is a direct evidence of direct interaction and energy transfer between SiNSs and UCNPs. We found that the SiNSs-UCNPs composite can be efficiently excited by at least two different light sources (UV and/or NIR lasers). The main discovery is related to the efficient absorption of UV radiation by SiNSs emitted by UCNPs, which in total can significantly reduce UV damage to cells and protect the biological object from photodegradation. Silicon-UCNPs system exhibit emission bands in the red-orange (650-800 nm) spectral range, which makes them in demand for the initiation of reactive oxygen species (ROS) photogeneration and as carriers of photodrugs that can be effectively used in theranostic applications.<br/>1 P V Maximchik, K Tamarov, E V Sheval, E Tolstik, T Kirchberger-Tolstik, Zh Yang, V Sivakov, B Zhivotovsky, and L A Osminkina, Biodegradable Porous Silicon Nanocontainers as an Effective Drug Carrier for Regulation of the Tumor Cell Death Pathways, ACS Biomater. Sci. Eng. 5(11), 6063–6071 (2019).<br/>2 E Tolstik, L A Osminkina, Ch Matthäus, M Burkhardt, K E Tsurikov, U A Natashina, V Yu Timoshenko, R Heintzmann, J Popp, V Sivakov, Studies of silicon nanoparticles uptake and biodegradation in cancer cells by Raman spectroscopy, Nanomedicine 12(7), 1931-1940 (2016).<br/>3. E Tolstik, MB Gongalsky, J Dierks, T Brand, M Pernecker, NV Pervushin, DE Maksutova, KA Gonchar, JV Samsonova, G Kopeina, V Sivakov, LA Osminkina, K Lorenz, Raman and fluorescence micro-spectroscopy applied for the monitoring of sunitinib-loaded porous silicon nanocontainers in cardiac cells, Front. Pharmacol. 13:962763 (2022).