Functionalizing the Mesoporous Silica Shell of Upconversion Nanoparticles To Enhance Bacterial Targeting and Killing via Photosensitizer-Induced Antimicrobial Photodynamic Therapy

Core–shell nanoparticles operating by infrared-to-visible energy upconversion (UCNPs) have been proposed as theranostic carriers for photosensitizers to increase deep-tissue penetration of photodynamic therapy against tumors and bacterial infections. Herein we present a series of core–shell mesoporous silica-coated NaYF4:Yb:Er UCNPs (mSiO2@UCNP) with different surface functionalizations to enhance bacterial targeting and loaded with the hydrophobic photosensitizer SiPc (silicon 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine dihydroxide) to boost the bactericidal effect against Gram-positive and Gram-negative bacteria upon near-infrared irradiation. Forster resonance energy transfer (FRET) from the UCNP core to loaded SiPc was facilitated, while its efficiency depended on UCNP shell functionalization, which influences the SiPc penetration depth into the mesoporous silica, constituting a convenient tool to modify FRET intensity. Functionalized UCNPs displayed dark toxicity toward Gram-negative E. coli of...