Broad-Spectrum Antimicrobial ZnMintPc Encapsulated in Magnetic-Nanocomposites with Graphene Oxide/MWCNTs Based on Bimodal Action of Photodynamic and Photothermal Effects

Abstract

Microbial diseases have been declared one of the main threats to humanity, which is why, in recent years, great interest has been generated in the development of nanocomposites with antimicrobial capacity. The present work studied two magnetic nanocomposites based on graphene oxide (GO) and multiwall carbon nanotubes (MWCNTs). The synthesis of these magnetic nanocomposites consisted of three phases: first, the synthesis of iron magnetic nanoparticles (MNPs), second, the adsorption of the photosensitizer menthol-Zinc phthalocyanine (ZnMintPc) into MWCNTs and GO, and the third phase, encapsulation in poly (N-vinylcaprolactam-co-poly(ethylene glycol diacrylate)) poly (VCL-co-PEGDA) polymer VCL/PEGDA a biocompatible hydrogel, to obtain the magnetic nanocomposites VCL/PEGDA-MNPs-MWCNTs-ZnMintPc and VCL/PEGDA-MNPs-GO-ZnMintPc. In vitro studies were carried out using Escherichia coli and Staphylococcus aureus bacteria and the Candida albicans yeast based on the Photodynamic/Photothermal (PTT/PDT) effect. This research describes the nanocomposites' optical, morphological, magnetic, and photophysical characteristics and their application as antimicrobial agents. The antimicrobial effect of magnetics nanocomposites was evaluated based on the PDT/PTT effect. For this purpose, doses of 65 mW·cm^-2 with 630 nm light were used. The VCL/PEGDA-MNPs-GO-ZnMintPc nanocomposite eliminated E. coli and S. aureus colonies, while the VCL/PEGDA-MNPs-MWCNTs-ZnMintPc nanocomposite was able to kill the three types of microorganisms. Consequently, the latter is considered a broad-spectrum antimicrobial agent in PDT and PTT.

Keywords: antimicrobial nanomaterials; carbon nanotubes; graphene; hydrogel; magnetic nanoparticles; nanocarrier; photodynamic therapy; photothermal therapy.

Figure 1

FT-IR spectra: (a) MNPs-MWCNTs; (b) MNPs-GO.

Figure 2

Raman Spectra: (a) non-purified MWCNTs, (b) purified MWCNTs, (c) MNPs-MWCNTs; (d) Fe-MNPs; (e) GO; (f) MNPs-GO; E_láser = 2.33 eV, λ = 532 nm.

Figure 3

Magnetic properties: (a) Magnetization vs. applied magnetic field: (i) the free-standing nanoparticles, (ii) VCL-PEGDA-MNPs-MWCNTs, and (iii) VCL-PEGDA-MNPs-GO. The curves shown reflect measurements at two different temperatures, T = −210 °C (circles) and T = 20 °C (triangles). The solid lines are examples of the fit of the data using the law of approach to saturation (LAS) of Equation (1). (b) Saturation magnetization as a function of temperature: (iv) the free-standing nanoparticles, (v) VCL-PEGDA-MNPs-MWCNTs and (vi) VCL-PEGDA-MNPs-GO. The solid lines match the data showing that MS follows Bloch’s law given Equation (2).

Figure 4

Stability curves over time for (a) VCL-PEGDA-ZnMintPc; (b) VCL/PEGDA-MNPs-MWCNTs-ZnMintPc and (c) VCL/PEGDA-MNPs-GO-ZnMintPc; ZnMintPc = 0.27 µM.

Figure 5

Decay curves of: VCL-PEGDA-ZnMintPc, VCL/PEGDA-MNPs-MWCNTs-ZnMintPc and VCL/PEGDA-MNPs-GO-ZnMintPc. ZnMintPc = 0.27 µM.

Figure 6

Decay curve of DPBF from (a) VCL/PEGDA-MNPs-GO and VCL/PEGDA-MNPs-MWCNTs; (b) VCL/PEGDA-MNPs-GO-ZnMintPc and VCL/PEGDA-MNPs-MWCNTs-ZnMintPc. DPBF = 18.5 mM, GO = 3.47 μg·mL⁻¹, MWCNTs = 3.47 μg·mL⁻¹, MNPs = 93.3 μg·mL⁻¹ and ZnMintPc = 8.1 μM.

Figure 7

Thermal studies. deionized water (control black line), VCL/PEGDA (red line), MNPs (blue line), GO (violet line), MWCNTs (light blue line), VCL/PEGDA-MNPs-GO (yellow line) and VCL/PEGDA-MNPs-MWCNTs (brown line). GO = 3.47 μg·mL⁻¹, MWCNTs = 3.47 μg·mL⁻¹, MNPs = 93.3 μg·mL⁻¹.

Figure 8

(a) SEM and TEM images of purified MWCNTs; (b) TEM of GO; (c) SEM of MNPs. (d) TEM of VCL/PEGDA-MNPs-MWCNTs-ZnMintPc. (e) TEM of VCL/PEGDA-MNPs-GO-ZnMintPc; (f) XRD analysis of MNPs-GO.

Figure 9

STEM of (a) S. aureus; (b) S. aureus + C1 (VCL/PEGDA-MNPs-GO-ZnMintPc); (c) S. aureus + C2(VCL/PEGDA-MNPs-MWCNTs-ZnMintPc); (d) E. coli; (e) E. coli + C1; (f) E. coli + C2.

Figure 10

PDT/PTT antimicrobial effect. Standardized result of LOG(UFC/mL) by (a) S. aureus; (b) E. coli and (c) C. albicans based in C1, C2, C3 and C4 nanocomposites. The concentration of MNPs in C1, C2, C3 and C4 was 93.3 μg·mL⁻¹. The concentration of ZnMintPc in C1 and C2 was 8.1 μM. The concentration of GO in C1 and C3 was 3.47 μg·mL⁻¹. The concentration of MWCNTs in C2 and C4 was 3.47 μg·mL⁻¹. Time of irradiation of C1 and C2 nanocomposites was 30 min and for C3 and C4 was 40 min. Significant differences in means according to the Tukey test (*** p ≤ 0.001).

Figure 11

Antimicrobial effect of C1 and C2 nanocomposites at C. albicans in vitro. C1: GO-MNPs-VGLPEGDA- ZnMintPc, C2: MWCNT-MNPs-VGLPEGDA- ZnMintPc, C3: GO-MNPs-VGLPEGDA, C4: MWCNT-MNPs-VGLPEGDA. The concentration of MNPs in C1, C2, C3 and C4 was 93.3 μg·mL⁻¹. The concentration of ZnMintPc in C1 and C2 was 8.1 μM. The concentration of GO in C1 and C3 was 3.47 μg·mL⁻¹. The concentration of MWCNTs in C2 and C4 was 3.47 μg·mL⁻¹.