Near infrared II excitation nanoplatform for photothermal/chemodynamic/antibiotic synergistic therapy combating bacterial biofilm infections

Abstract

Drug-resistant bacterial biofilm infections (BBIs) are refractory to elimination. Near-infrared-II photothermal therapy (NIR-II PTT) and chemodynamic therapy (CDT) are emerging antibiofilm approaches because of the heavy damage they inflict upon bacterial membrane structures and minimal drug-resistance. Hence, synergistic NIR-II PTT and CDT hold great promise for enhancing the therapeutic efficacy of BBIs. Herein, we propose a biofilm microenvironment (BME)-responsive nanoplatform, BTFB@Fe@Van, for use in the synergistic NIR-II PTT/CDT/antibiotic treatment of BBIs. BTFB@Fe@Van was prepared through the self-assembly of phenylboronic acid (PBA)-modified small-molecule BTFB, vancomycin, and the CDT catalyst Fe²⁺ ions in DSPE-PEG₂₀₀₀. Vancomycin was conjugated with BTFB through a pH-sensitive PBA-diol interaction, while the Fe²⁺ ions were bonded to the sulfur and nitrogen atoms of BTFB. The PBA-diol bonds decomposed in the acidic BME, simultaneously freeing the vancomycin and Fe²⁺ irons. Subsequently, the catalytic product hydroxyl radical was generated by the Fe²⁺ ions in the oxidative BME overexpressed with H₂O₂. Moreover, under 1064 nm laser, BTFB@Fe@Van exhibited outstanding hyperthermia and accelerated the release rate of vancomycin and the efficacy of CDT. Furthermore, the BTFB@Fe@Van nanoplatform enabled the precise NIR-II imaging of the infected sites. Both in-vitro and in-vivo experiments demonstrated that BTFB@Fe@Van possesses a synergistic NIR-II PTT/CDT/antibiotic mechanism against BBIs.

Keywords: Bacterial biofilm infection; Chemodynamic therapy; NIR-II light excitation; NIR-II photothermal therapy; pH-responsive nanoplatform.

Scheme 1

Schematic illustration of a BME-responsive nanoplatform BTFB@Fe@Van and its synergistic treatment for eradicating drug-resistant BBIs

Fig. 1

a Structural formula of NIR-II organic small molecule BTF-PBA. b Average hydrodynamic diameters of the synthesized BTFB, BTFB@Fe, BTFB@Van, and BTFB@Fe@Van using DLS. c TEM image of BTFB@Fe@Van. d Zeta potentials of BTFB and BTFB@Fe@Van in water. e Energy-dispersive spectroscopy elemental mapping diagram of BTFB@Fe@Van. Scale bar: 50 nm. f Absorption and NIR-II fluorescence spectrum of BTFB@Fe@Van under 808 nm laser excitation. (Inset: NIR-II images of BTFB@Fe@Van under 808 nm laser excitation with a 1064 nm filter)

Fig. 2

a Photothermal heating curves of water and BTFB@Fe@Van (0.1 mg mL⁻¹) under 1064 nm laser irradiation (1.0 W cm⁻²). b Linear correlation between the cooling time and negative natural logarithm of the driving force temperature. c Photothermal stability of BTFB@Fe@Van over five on/off cycles. d ·OH generation quantified from the decrease in MB absorbance at 664 nm ([BTFB@Fe@Van] = 0.1 mg mL⁻¹, [H₂O₂] = 0.1 mM, and [MB] = 1.0 mM) with different treatments [pH 7.4, pH 5.5, and pH 5.5 with 1064 nm laser irradiation (1.0 W cm⁻²)]. e ESR spectra of the aqueous solutions of BTFB@Fe@Van under different conditions ([H₂O₂] = 0.1 mM, and [H₂O₂] = 0.1 mM with 1064 nm laser irradiation (1.0 W cm⁻²)). f Van release from BTFB@Fe@Van under different environments (pH 7.4, pH 5.5, and pH 5.5 with 1064 nm laser irradiation (1.0 W cm⁻²)

Fig. 3

a Live/dead assay after different treatments. Scale bars: 100 μm. b Photographs of the LB agar plates of S. aureus after different treatments. c Bacterial viability of I: PBS, II: Van, III: BTFB, IV: BTFB@Fe, and V: BTFB@Fe@Van after different treatments. d SEM images of the bacteria after different treatments. Scale bars: 1 μm

Fig. 4

a Crystal violet staining of S. aureus biofilms after different treatments. b The corresponding quantified biomass of the biofilms of I: PBS, II: Van, III: BTFB, IV: BTFB@Fe, and V: BTFB@Fe@Van. c Three-dimensional CLSM images showing live/dead staining of S. aureus biofilms after different treatments (scale bars: 100 μm)

Fig. 5

a NIR-II fluorescence images and b corresponding quantified NIR-II fluorescence signals of the infected mouse models at different time intervals. c Infrared photothermal images and d corresponding temperature variations at the infected sites with PBS or BTFB@Fe@Van treatment under 1064 nm laser irradiation (1.0 W cm⁻², 5 min)

Fig. 6

a Time line guidance for antibiofilm therapeutic process. b Digital photographs of the lesion site between 0 and 12 d after different treatments. c Photographs of the LB agar plates of S. aureus of the resected lesion site 12 d after the injection. d Quantitative analysis of the relative wound area throughout the therapeutic process. e, f Serum levels of cytokines IL-6 and TNF-α in I: Saline, II: Van, III: BTFB@Fe, IV: BTFB@Fe + 1064 nm laser, V: BTFB@Fe@Van, and VI: BTFB@Fe@Van + 1064 nm laser groups after different treatments

Fig. 7

Representative a H&E staining and b Masson staining images of the wound subjected to different treatments. Scale bars: 200 μm

Fig. 8

a Routine blood indexes of mice after different treatments at day 14 post-injection. b H&E staining effect of the main organ sections of the mice on I: Saline, II: BTFB@Fe, and III: BTFB@Fe@Van 14 d after the injection. Scale bar: 100 μm