Protein-based nanocarriers for antimicrobial photodynamic therapy and subdiffraction localization of the theranostic agent

Nano-structures for photodynamical therapy can be assembled starting from a photosensitizer (PS) and a protein-based carrier, exploiting hydrophobic interactions. These chemical constructs preserve the PS photophysical and photosensitizing properties by preventing aggregation of non water-soluble PSs. This allows to obtain bio-compatible nanostructures that enhance the bio-availability of the PS. We demonstrate the interaction of Hypericin (Hyp), a naturally occurring PS that generates singlet oxygen with a high quantum yield, with two different proteins, apo-myoglobin and β-lactoglobulin. The constructs are highly effective against Gram-positive bacteria (S. aureus and B. subtilis). Interestingly, Hyp both free and bound to the protein can be exploited in super-resolution STED fluorescence microscopy, allowing for an accurate localization at cellular level of the PS and the photoinduced oxidation effects. Therefore, these structures show a double functionality, both therapeutic (based on photosensitization) and diagnostic (based on imaging),so that they can be considered theranostic agents. In conclusion, we demonstrate the potential of the protein-based nanostructures as water soluble and bio-compatible systems that can be relevant for applications in antimicrobial decontamination, both in clinical and in food and food-processing environment applications