InP-Based Quantum Dots as Photosensitizers in Photodynamic Antimicrobial Materials

Ligand-functionalized InP-based quantum dots (QDs) have been developed as an innovative class of nontoxic photosensitizer suitable for antimicrobial applications, aimed at reducing or preventing pathogen transmission from one host to another via high contact surfaces. A hot injection method followed by functionalization via ligand exchange with 9-anthracene carboxylic acid (ACA) yielded the desired core/shell InP/ZnSe/ZnS QDs. Transmission electron microscopy (TEM) revealed these QDs to be uniform in size (∼3.2 nm), with light absorption across the entire visible spectrum (λ_max ∼550 nm). Under light excitation at 550 nm, the generation of singlet oxygen (¹O₂) was evidenced by its characteristic phosphorescence signal at 1278 nm, indicating successful energy transfer from the QDs to surface-anchored ACA ligands, in accordance with a type II mechanism for a photodynamically generated singlet oxygen. The InP/ZnSe/ZnS core/shell QDs were applied to cellulose via dip coating, and the resultant QDs-loaded material was assessed for antimicrobial photodynamic inactivation (aPDI) of both Gram-positive [methicillin-resistant Staphylococcus aureus (MRSA; ATCC-44), vancomycin-resistant Enterococcus faecium (VRE; ATCC-2320)] and Gram-negative [multidrug-resistant Acinetobacter baumannii (MDRAB; ATCC-1605), NDM-1 positive Klebsiella pneumoniae (KP; ATCC-2146)] bacteria under illumination (400-700 nm; 85 mW/cm²; 90 min). The highest inactivation was observed for MRSA, achieving at least 99.999% inactivation (5 log units). Antiviral photodynamic inactivation on human coronavirus 229E (HCoV-229E) and feline calicivirus (FCV) demonstrated complete viral inactivation (to the detection limit). Cytotoxicity studies showed that the QDs are nontoxic to mammalian cells in the dark. Together, these results confirm the promising potential of ligand-functionalized InP-based QDs to be employed as nontoxic photosensitizers as materials in self-sterilizing surfaces.