Mn-doped Zn/S quantum dots as photosensitizers for antimicrobial photodynamic inactivation

The survival of pathogens on surfaces is a major contributor to infection transmission, and drives the development of self-sterilizing surfaces. Here, we have investigated if manganese-doped zinc sulfide quantum dots (Mn:ZnS QDs) can be used as photosensitizers for their potential application in surface disinfection via antimicrobial photodynamic inactivation (aPDI). A small library of Mn: ZnS QDs capped with 3-mercaptopropionic acid was synthesized using a hydrothermal approach in which both the amount of manganese (0-30 at.%) and heating period (9 - 20 h) were varied. The resultant Mn:ZnS QDs were shown by transmission electron microscopy to vary in size from 2.6-3.9 angstrom as a function of heating time, and exhibited a strong emission band at similar to 598 nm (lambda(ex) = 325 nm). Upon excitation of 5%-Mn: ZnS QDs at 514 nm, a near-IR emission band attributable to singlet oxygen phosphorescence was observed at 1278 nm, confirming that these QDs may function as photosensitizers via a Type II mechanism. The aPDI efficacy of the Mn:ZnS QDs was evaluated against both Gram-positive [methicillin-resistant S. aureus (MRSA; ATCC-44), vancomycin-resistant E. faecium (VRE; ATCC-2320)], and Gram-negative [multidrug-resistant A. baumannii (MDRAB; ATCC-1605), NDM-1 positive K. pneumoniae (KP; ATCC-2146)] bacteria. Our best results demonstrated detection limit photodynamic inactivation (6 log units reduction) of KP, MDRAB, and MRSA upon illumination (30 min; 65 +/- 5 mW/cm(2); 400-700 nm), but only a similar to 1 log unit reduction against VRE. Together with antiviral studies of Zika virus that showed similar to 3 log units of inactivation, these findings demonstrate the utility of Mn:ZnS QDs as photosensitizers for aPDI.