Facile Multistep Synthesis of ZnO-Coated β-NaYF₄:Yb/Tm Upconversion Nanoparticles as an Antimicrobial Photodynamic Therapy for Persistent Staphylococcus aureus Small Colony Variants

Abstract

Antibacterial treatment strategies using functional nanomaterials, such as photodynamic therapy, are urgently required to combat persistent Staphylococcus aureus small colony variant (SCV) bacteria. Using a stepwise approach involving thermolysis to form β-NaYF 4 :Yb/Tm upconversion nanoparticles (UCNPs) and surface ligand exchange with cetyltrimethylammonium bromide (CTAB), followed by zeolite imidazolate framework-8 (ZIF-8) coating and conversion to zinc oxide (ZnO), β-NaYF 4 :Yb/Tm@ ZnO nanoparticles were synthesized. The direct synthesis of β-NaYF 4 :Yb/Tm@ZIF-8 UCNPs proved problematic due to the hydrophobic nature of the as-synthesized material, which was shown by zeta potential measurements using dynamic light scattering (DLS). To facilitate deposition of a ZnO coating, the zeta potentials of (i) as-synthesized UCNPs, (ii) calcined UCNPs, (iii) polyvinylpyrrolidone (PVP), and (iv) CTAB-coated UCNPs were measured, which revealed the CTAB-coated UCNPs to be the most hydrophilic and the better-dispersed form in water. β-NaYF 4 :Yb/Tm@ZIF-8 composites formed using the CTAB-coated UCNPs were then converted into β-NaYF 4 :Yb/Tm@ZnO nanoparticles by calcination under carefully controlled conditions. Photoluminescence analysis confirmed the upconversion process for the UCNP core, which allows the β-NaYF 4 :Yb/Tm@ZnO nanoparticles to photogenerate reactive oxygen species (ROS) when activated by near-infrared (NIR) radiation. The NIR-activated UCNPs@ZnO nanoparticles demonstrated potent efficacy against both Staphylococcus aureus (WCH-SK2) and its associated SCV form (0.67 and 0.76 log colony forming unit (CFU) reduction, respectively), which was attributed to ROS generated from the NIR activated β-NaYF 4 :Yb/Tm@ZnO nanoparticles.

Rare earth-doped nanocrystals for bioimaging in the near-infrared region

“…For example, polyacrylic acid (PAA) replaces OA ligands, [88][89][90] and PEG 600 diacid (HOOC-PEG-COOH) replaces OM or OA ligands. 91,92 In addition, it has been shown that polyvinylpyrolidone (PVP), 77,93 3-mercaptopropionic acid (3MA), 94 adipic acid (HDA) 95 and cetyltrimethylammonium bromide (CTAB) 96 can be used for ligand exchange modification experiments. Ligand oxidation achieves functional modification by oxidizing ligands on the surface of nanoparticles.…”

Upconversion nanoparticles and its based photodynamic therapy for antibacterial applications: A state-of-the-art review

“…Hence, using UCNPs combined with NIR, the undesirable aspects of UV- and visible light-activated material can be accordingly addressed. As an example, Figure 3 illustrates the APDT mechanism of NaYF 4 : Yb 3+ /Er 3+ @ZnO ( Karami et al, 2021 ).…”

“… The dopant Yb 3+ and Tm 3+ ions convert 980 nm of NIR light into UV light. The ZnO in the outer layer of the core-shell structure absorbs UV light to produce ROS and achieve the antibacterial effect ( Karami et al, 2021 ). …”

UV Emission from Lanthanide-Doped Upconversion Nanoparticles in Super-Resolution Microscopy: Potential for Cellular Damage

“…While some studies intentionally generate UV light from UCNPs to directly influence or kill cells, − most imaging applications do not consider the emissions in this range. This raises questions as to whether some UCNPs have significant energetic UV emissions that are not being detected, commonly due to most spectral systems having difficulty readily characterizing UV emissions.…”