Blue light activated photodegradation of biomacromolecules by N-doped titanium dioxide in a chitosan hydrogel matrix

The use of photocatalysis activated by titanium dioxide nanostructured materials is a promising solution for many biomedical applications ranging from drug-free antibacterial to anticancer therapies, as well as for innovative hydrogel-supported phototherapies. This makes the effects of photocatalysis on the structure of biomolecules of a great relevance in order to define the applicability of photocatalytic materials in the biomedical fields. In this work, the effects of nitrogen-doped titanium dioxide (N-TiO2) dispersed in a biocompatible chitosan/PEG hydrogel on myoglobin and bovine serum albumin as target model proteins were investigated. The efficiency of this composite biocompatible material in inducing damages on biomolecules was assessed under blue light illumination by using spectroscopic techniques. N-TiO2 nanoparticles were chosen as photocatalyst to trigger the photocatalytic process by irradiation with a blue light source, instead of higher energy sources, e.g. UV radiation, avoiding UV-related damages on biomolecules. In addition, the present work highlighted several advantages of using the hydrogel as medium for photocatalytic reactions. Firstly, N-TiO2 nanoparticles were well dispersed and stabilized in the hydrogel respect to the correspondent aqueous suspension, and the photocatalytic reactions can occur in a biomimetic and biocompatible environment suitable for biomolecules, such as proteins. Importantly, the chitosan/PEG hydrogel enabled a direct investigation of the effects of photocatalysis on proteins by direct in situ spectroscopic measurements without any need of recovery of the target molecules, nor stirring during the photocatalysis, which could be detrimental for delicate biomolecules structures. Finally, the possibility to run in situ spectroscopic measurements directly in the N-TiO2-loaded hydrogel during the photocatalytic process allowed kinetic studies of photocatalytic process to obtain information of the chemical and structural modifications of proteins over time and not only at the end of the photocatalysis. Therefore, the reported results highlight the possibility of using this system as biomimetic environment to investigate the photocatalysis of proteins in detail overcoming relevant technical aspects that typically limit the study of photocatalysis of biomolecules, opening up the possibility to extend the approach to more complex biomolecular systems.