Harmonization of upconverting nanocrystals and photosensitizer for antimicrobial application

Abstract

Although the loading of photosensitizers onto upconverting nanoparticles (UCs) has been demonstrated previously, none of the research works has perfected the matching between absorption wavelengths of the loaded photosensitizers and emission wavelengths from UCs. Therefore not all visible emissions from UCs are used purposefully. In addition, low upconversion of near infrared radiations into UV-visible emissions by the UCs has hindered applications of the materials. Here we show that by optimizing the doping amount of Tm³⁺ in the Yb³⁺-doped NaYF₄ lattice and constructing a NaYF₄ shell around the optimized [Yb³⁺, Tm³⁺-doped NaYF₄ core], UVA and visible emissions can be tremendously increased. We also synthesize meso-tetraphenyltetrabenzoporphyrinatozinc (ZnTPTBP), a photosensitizer whose absorption wavelengths match perfectly with the visible emission wavelengths of the obtained UCs. We then load the ZnTPTBP onto the optimized UCs and verify an ability of the ZnTPTBP-loaded UCs to effectively generate excited singlet oxygen species upon NIR irradiation using 9,10-anthracenediyl-bis(methylene)dimalonic acid as a singlet oxygen fluorescence probe, and sodium azide as a singlet oxygen scavenger. Effective eradication of Propionibacterium acnes (P. acnes) by a combination of ZnTPTBP-loaded UCs and 980 nm laser is verified in vitro. This anti-P. acnes application demonstrates the total utilization of both UVA and visible emissions from the UCs; the direct excitation of P. acnes porphyrins by UVA emission, and the excitation of the loaded ZnTPTBP by the visible emissions which results in the production of reactive oxygen species that harm the bacteria. This work not only demonstrates an antibacterial application of UCs with high UV-visible upconverted emissions, but also shows the perfect tailoring of the materials based on the harmony between upconversion emissions and photosensitizer absorptions.