Abstract
Lignin has recently attracted the attention of the scientific community, as a suitable raw material for biomedical applications. In this work, acetylated lignin was used to encapsulate five different porphyrins, aiming to preserve their photophysical properties, and for further use as antibacterial treatment. The obtained nanoparticles were physically characterized, through dynamic light scattering size measurement, polydispersity index and zeta potential values. Additionally, the photophysical properties of the nanoparticles, namely UV-vis absorption, fluorescence emission, singlet oxygen production and photobleaching, were compared with those of the free porphyrins. It was found that all the porphyrins were susceptible to encapsulation, with an observed decrease in their fluorescence quantum yield and singlet oxygen production. These nanoparticles were able to exert an effective photodynamic bactericide effect (blue-LED light, 450–460 nm, 15 J/cm2) on Staphylococcus aureus and Escherichia coli. Furthermore, it was achieved a photodynamic bactericidal activity on an encapsulated lipophillic porphyrin, where the free porphyrin failed to diminish the bacterial survival. In this work it was demonstrated that acetylated lignin encapsulation works as a universal, cheap and green material for the delivery of porphyrins, while preserving their photophysical properties.
Highlights
Antimicrobial resistance (AMR) is one of major threats to our current way of life, with enduring humanitarian and economic consequences if not addressed assertively [1]
The role of hydroxyl seems to be important for their hydrophilic character, as solubility and encapsulation efficiency, as well as for their possible antioxidant properties [27]
These targeted compounds have been designed for the sake of comparison and for a better understanding of the hydroxyl group role in the whole studied system
Summary
Antimicrobial resistance (AMR) is one of major threats to our current way of life, with enduring humanitarian and economic consequences if not addressed assertively [1]. Conventional antibiotics’ bacterial resistance advocates exploring less resistance-prone therapeutic approaches [6], where photodynamic antimicrobial chemotherapy (PACT) [7] has proved as an efficient alternative in the inactivation of several bacterial strains [8,9,10,11,12,13] This therapeutic strategy involves the concomitant use of a light source in appropriate dosage, a photosensitizer molecule and molecular oxygen, generating reactive oxygen species (ROS), namely singlet oxygen (1O2), super oxide anion (O2−), and hydroxyl radical (HO). These ROS produce oxidative stress in bacteria through a non-specific molecular target mechanism, which ensures cellular death without risk of antimicrobial resistance [14]. The role of lignin in the preparation of nanomaterials for loading and release of active substances is under growing scientific scrutiny [16]
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