Antibacterial and antibiofilm properties of yttrium fluoride nanoparticles

Figures & data

Figure 1 General view of the synthesis of YF₃ NPs and NP deposition on a surface by sonochemistry.

Notes: YF₃ (black stars) is formed under ultrasonic irradiation (red waves). Microjets (blue arrows) are formed after the collapse of the acoustic bubble near the catheter wall and eject the NPs to create a YF₃ NP coating.

Abbreviations: NP, nanoparticle; YF₃, yttrium fluoride.

Figure 2 YF₃ NP characterization. (A) SEM micrograph and (B) X-ray elemental spectra of YF₃ NPs. Percentages indicated in (B) refer to the relative atomic ratio between fluor and yttrium atoms. (C and D) Nanoparticle length and width distributions.

Abbreviations: NP, nanoparticle; SEM, scanning electron microscope; YF₃, yttrium fluoride.

Figure 3 YF₃ NP crystallinity characterization. (A) Powder XRD analysis of the crystalline NPs. The XRD pattern matched the reflection peaks and relative Miller indices of orthorhombic YF₃. (B) HR-TEM micrographs of YF₃ NPs and (C) characteristic lattice fringes of the crystalline phases indicated by the black arrow in (B). (D) Selected area diffraction patterns of polycrystalline YF₃ NPs shown in (B).

Abbreviations: HR-TEM, high-resolution transmission microscope; NP, nanoparticle; XRD, X-ray diffraction; YF₃, yttrium fluoride.

Figure 4 Antimicrobial effect of YF₃ NPs. Growth curves of (A) Escherichia coli and (B) Staphylococcus aureus exposed to variable concentrations (0.0001 to 1 mg/mL) of YF₃ NP solutions for 24 hours at 37°C.

Notes: Untreated bacteria served as a control. Error bars represent the standard deviation of three independent experiments conducted in triplicate. The results were found to be statistically significant (P < 0.05) between control versus NP-treated cells in all treatments.

Abbreviations: NP, nanoparticle; OD₅₉₅, optical density at 595 nm; YF₃, yttrium fluoride.

Figure 5 Influence of solubility of YF₃ and MgF₂ NPs on the F⁻ intracellular and extracellular concentrations.

Notes: Fluorine intracellular ([F⁻]_in, columns-left y axis) and extracellular (ie, fluorine concentration in the surrounding media, noted at [F⁻]_ex and represented by circles-right y axis) concentrations of Escherichia coli and Staphylococcus aureus exposed to MgF₂ and YF₃ NPs at a concentration of 0.01 mg/mL for 2 hours at 37°C. Error bars represent the standard deviation of three independent experiments conducted in triplicate. Each circle represents the mean of one experiment conducted in triplicate. (Insert) The MICs of E. coli and S. aureus exposed, respectively, to MgF₂ and YF₃ NPs (taken from Figures 4 and S2).

Abbreviations: [F⁻]_ex, fluorine extracellular concentration; [F⁻]_in, fluorine intracellular concentration; MgF₂, magnesium fluoride; MICs, minimal inhibitory concentrations; NPs, nanoparticles; YF₃, yttrium fluoride.

Figure 6 Antibiofilm properties of YF₃ NPs.

Notes: Biofilm formation quantified after overnight incubation for (A) Escherichia coli and (B) Staphylococcus aureus exposed to variable concentrations (0.0001 to 1 mg/mL) of YF₃ NP solutions for 24 hours at 37°C.

Notes: Untreated bacteria served as a control. Error bars represent the standard deviation of three independent experiments. The results were found to be statistically significant (P < 0.05) between control versus NP-treated cells in all treatments.

Abbreviations: NP, nanoparticle; OD₅₉₅, optical density at 595 nm; YF₃, yttrium fluoride.

Table 1 Characterization of YF₃ particles of different size

Sample	Debye–Scherrer (nm)	DLS (nm)	BET (m^2/g)
YF3-1	358	365 ± 30	20.21
YF3-2	150	156 ± 26	97.01
YF3-3	49	51 ± 10	145.32

Note: Average particle sizes (Debye–Scherrer formula), DLS, and BET multipoint surface area measurements of YF₃ NP samples.

Abbreviations: BET, Brunauer–Emmett–Teller; DLS, dynamic light scattering; YF₃, yttrium fluoride.

Figure 7 Impact of size of YF₃ NPs on antimicrobial activity.

Notes: Growth yields of Escherichia coli and Staphylococcus aureus grown in the presence of YF₃ NP (0.001 mg/mL) suspension at different sizes (samples 1–3) for 24 hours at 37°C. Untreated bacteria served as a control. Error bars represent the standard deviation of three independent experiments. The results were found to be statistically significant (P < 0.05) between control versus NP-treated cells in all treatments.

Abbreviations: NP, nanoparticle; OD₅₉₅, optical density at 595 nm; YF₃, yttrium fluoride.

Figure 8 Imaging and characterization of sonochemical YF₃ NP catheter coating.

Notes: Catheters were coated using a sonochemical procedure described in the experimental section. SEM images of the internal walls of uncoated and YF₃ NP-coated catheters are presented. The distribution of the YF₃ NP coating on the catheter’s surface characterized by X-ray dot mapping of yttrium (red) and fluor (purple) atoms signals detected on the internal catheter wall.

Abbreviations: K, K line energy; NP, nanoparticle; SEM, scanning electron microscope; YF₃, yttrium fluoride.

Figure 9 Antibiofilm properties of the catheter coated with YF₃ NPs against formation of biofilms by Escherichia coli and Staphylococcus aureus.

Notes: Viable counts of the biofilm cells of E. coli and S. aureus, grown in TSB and TSB-Glu, on the internal wall of a YF₃ NP-coated catheter incubated for 24 hours at 37°C. Uncoated catheters served as the negative control. Bars represent the standard deviation of three independent experiments conducted in triplicate. The results were found to be statistically significant (P < 0.05) between uncoated versus NP-coated catheters in all treatments.

Abbreviations: CFU, colony forming units; NP, nanoparticle; TSB, tryptic soy broth; TSB-Glu, tryptic soy broth supplemented with 0.2% glucose; YF₃, yttrium fluoride.

Figure S1 Growth curves (A) and biofilm formation (B) of Escherichia coli and Staphylococcus aureus exposed to fluorine (100 μg/mL) and yttrium ions (100 μg/mL) for 24 hours at 37°C.

Notes: Untreated bacteria served as a control. Error bars represent the standard deviation of three independent experiments conducted in triplicate.

Abbreviation: OD₅₉₅, optical density at 595 nm.

Figure S2 Antimicrobial effect of MgF₂ NPs. Growth curves of (A) Escherichia coli and (B) Staphylococcus aureus exposed to variable concentrations (0.0001 to 1 mg/mL) of MgF₂ NP solutions for 24 hours at 37°C.

Notes: Untreated bacteria served as a control. Error bars represent the standard deviation of three independent experiments conducted in triplicate.

Abbreviations: MgF₂, magnesium fluoride; OD₅₉₅, optical density at 595 nm; NPs, nanoparticles.