Nanostructured N/S doped carbon dots/mesoporous silica nanoparticles and PVA composite hydrogel fabrication for anti-microbial and anti-biofilm application

Abstract

Regarding the convergence of the worldwide epidemic, the appearance of bacterial infection has occasioned in a melodramatic upsurge in bacterial pathogens with confrontation against one or numerous antibiotics. The implementation of engineered nanostructured particles as a delivery vehicle for antimicrobial agent is one promising approach that could theoretically battle the setbacks mentioned. Among all nanoparticles, silica nanoparticles have been found to provide functional features that are advantageous for combatting bacterial contagion. Apart from that, carbon dots, a zero-dimension nanomaterial, have recently exhibited their photo-responsive property to generate reactive oxygen species facilitating to enhance microorganism suppression and inactivation ability. In this study, potentials of core/shell mesoporous silica nanostructures (MSN) in conjugation with carbon dots (CDs) toward antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli have been investigated. Nitrogen and sulfur doped CDs (NS/CDs) conjugated with MSN which were cost effective nanoparticles exhibited much superior antimicrobial activity for 4 times as much as silver nanoparticles against all bacteria tested. Among all nanoparticles tested, 0.40 M NS/CDs@MSN showed the greatest minimal biofilm inhibitory at very low concentration (< 0.125 mg mL^-1), followed by 0.20 M NS/CDs@MSN (0.5 mg mL^-1), CD@MSN (25 mg mL^-1), and MSN (50 mg mL^-1), respectively. Immobilization of NS/CDs@MSN in polyvinyl alcohol (PVA) hydrogel was performed and its effect on antimicrobial activity, biofilm controlling efficiency, and cytotoxicity toward fibroblast (NIH/3 T3 and L-929) cells was additionally studied for further biomedical applications. The results demonstrated that 0.40 M NS/CDs-MSN@PVA hydrogel exhibited the highest inhibitory effect on S. aureus > P. aeruginosa > E. coli. In addition, MTT assay revealed some degree of toxicity of 0.40 M NS/CDs-MSN@PVA hydrogel against L-929 cells by a slight reduction of cell viability from 100% to 81.6% when incubated in the extract from 0.40 M NS/CDs-MSN@PVA hydrogel, while no toxicity of the same hydrogel extract was detected toward NIH/3 T3 cells.

Keywords: Antimicrobial activity; Carbon dots; Cytotoxicity test; Freeze-thaw technique; Health and well-being; MTT assay; Mesoporous silica nanostructures; Polyvinyl alcohol hydrogel.

Graphical abstract

Scheme 1

Schematic illustration of the preparation of mesoporous silica nanoparticles (MSN) and CDs@MSN or NS/CDs@MSN nanocomposites

Fig. 1

(A) UV–Vis absorption spectra of CDs@MSN, 0.20 M NS/CDs@MSN, 0.40 M NS/CDs@MSN, and MSN; (B) Photographs of samples (B1) under natural light and (B2) under UV at 365 nm; Fluorescence intensity of (C) MSN, (D) CDs@MSN, (E) 0.20 M NS/CDs@MSN, and (F) 0.40 M NS/CDs@MSN when the excitation wavelength varied from ∼270 to ∼370 nm.

Fig. 2

(A) the relationship between relative pressure (P/P₀) and adsorbed volume of nitrogen gas, and (B) the plots of dV/dD pore volume versus pore diameter during adsorption of CDs@MSN, 0.20 M NS/CDs@MSN, 0.40 M NS/CDs@MSN and MSN samples.

Fig. 3

FESEM imaging of different samples: (A) CDs@MSN, (B) 0.20 M NS/CDs@MSN, (C) 0.40 M NS/CDs@MSN, and (D) MSN after reflux in the form of mesoporous silica nanoparticles.

Fig. 4

FETEM imaging of different samples: (A) CDs@SiO₂, (B) 0.20 M NS/CDs@SiO₂, (C) 0.40 M NS/CDs@SiO₂, and (D) SiO₂ before reflux in the form of SiO₂ when 1) FETEM images at 10,000× or 30,000× magnification, 2) FETEM images at 100,000× magnification, and 3) average diameter and size distribution of nanoparticles.

Fig. 5

FETEM imaging of different samples: (A) CDs@MSN, (B)0.20 M NS/CDs@MSN, (C)0.40 M NS/CDs@MSN and (D) MSN after reflux in the form of mesoporous silica nanoparticles (MSN) when 1) FETEM images at 10,000× or 30,000× magnification, 2) FETEM images at 100,000× magnification, and 3) average diameter and size distribution of nanoparticles.

Fig. 6

XRF data analysis of different samples: (A) CDs@MSN, (B) 0.20 M NS/CDs@MSN, (C) 0.40 M NS/CDs@MSN and (D) MSN after reflux in MSN form.

Fig. 7

High resolution XPS spectra of (A) CDs@MSN, (B) 0.20 M NS/CDs@MSN, (C) 0.40 M NS/CDs@MSN, and (D) MSN for [1] Survey, [2] O 1 s, [3] C 1 s, [4] Si 2p, and [5] N 1 s.

Fig. 8

Appearance of carbon dots and MSN@PVA hydrogels under (A) natural light, (B) UV light at 254 nm, and (C) UV light at 365 nm.

Fig. 9

(A) TGA, (B) DTG profiles, and (C) DSC patterns of CDs, NS/CDs, CDs@MSN, NS/CDs@MSN PVA hydrogels.

Scheme 2

The schematic illustration of antibiofilm activity of NS/CDs@MSN in PVA hydrogel from repeatedly freezing-thawing technique.

Fig. 10

Cell viability using MTT assay (A) 0.40 M NS/CDs@PVA hydrogel extract, and (B) 0.40 M NS/CDs-MSN@PVA hydrogel extract toward NIH/3 T3 cells, and (C) 0.40 M NS/CDs@PVA hydrogel extract, and (D) 0.40 M NS/CDs-MSN@PVA hydrogel extract toward L-929 cells.