Squaraine-loaded mesoporous silica nanoparticles for antimicrobial Photodynamic Therapy against bacterial infection

Antimicrobial photodynamic therapy (aPDT) shows promise as a complementary or alternative approach to conventional antimicrobial treatments. Despite possessing some key advantages, many challenges remain, such as optimizing the delivery of photosensitizers, improving light penetration into tissues, and determining the most effective combinations of photosensitizers and light wavelengths for different infections. Moreover, addressing the challenges associated with the aggregation tendency and poor solubility of some photosensitizers, squaraine dyes (SQs) in particular, is crucial for unlocking their full potential in biomedical applications. This contribution focuses on designing innovative nanophotosensitizers with antimicrobial properties using mesoporous silica nanoparticles (MSNs) loaded with a SQ dye (i.e. Br-SQ). MSNs before and after Br-SQ loading were deeply characterized using different techniques, proving the successful incorporation of the dye into the nanocarriers. Upon visible light (640 nm) irradiation, these nanosystems demonstrated remarkable antibacterial activities against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). Our results confirmed that MSNs are valuable nanocarriers of hydrophobic photosensitizers, such as Br-SQ, bringing up new opportunities to develop antibiotic-free nanoformulations to treat bacterial infection while minimizing the risk of antimicrobial resistance.