A versatile and environmentally friendly formulation for porphyrins: lignin nanoparticles and their application in photodynamic antimicrobial chemotherapy

Background Photodynamic antimicrobial therapy aims to develop disinfecting strategies using light, oxygen and a photosensitizer molecule, to form reactive oxygen species, capable of unspecifically killing bacteria, without the risk of developing antimicrobial resistance. However, most photosensitizers are prone to highly aggregate in aqueous media, diminishing their efficiency. Aiming to avert this, the use of photosensitizers conjugated in bio-based formulations is a topic that has been received with enthusiasm by the scientific community1. Results In the present work, as part of the project POLYTHEA (http://www.polythea.eu/), we developed a formulation based in acetylated lignin nanoparticles for the transport of five different porphyrin compounds2. The loaded nanoparticles were fully characterized and the nanoparticles were tested against a Gram-negative (Escherichia coli) and a Gram-positive (Staphylococcus aureus) bacteria. Depending on the nature of the photosensitizer (cationic or non-cationic), the nanoparticles were able to affect the survival of E. coli, while most of them were efficient against S. aureus. Interestingly, the formulation attenuated a dark toxicity effect found for the free photosensitizers. Discussion The intended formulation was able to be loaded with the five selected photosensitizers, proving to be a versatile nanoconjugate. Furthermore, the formulation was stable and its efficiency against bacteria was demonstrated against model Gram-positive bacteria. Continuous efforts are being made to increase the knowledge on this type of formulation upon encapsulation of other types of photosensitizers (i.e., phthalocyanines, natural compounds, chlorins), while providing an aggregated value to an abundant natural polymer such as lignin.