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. 2023 May 17;12(5):919.
doi: 10.3390/antibiotics12050919.

Employing Gamma-Ray-Modified Carbon Quantum Dots to Combat a Wide Range of Bacteria

Zoran M Marković  1 , Aleksandra S Mišović  1 , Danica Z Zmejkoski  1 , Nemanja M Zdravković  2 , Janez Kovač  3 , Danica V Bajuk-Bogdanović  4 , Dušan D Milivojević  1 , Marija M Mojsin  5 , Milena J Stevanović  5   6   7 , Vladimir B Pavlović  8 , Biljana M Todorović Marković  1
Affiliations

Employing Gamma-Ray-Modified Carbon Quantum Dots to Combat a Wide Range of Bacteria

Zoran M Marković et al. Antibiotics (Basel). .

Abstract

Nowadays, it is a great challenge to develop new medicines for treating various infectious diseases. The treatment of these diseases is of utmost interest to further prevent the development of multi-drug resistance in different pathogens. Carbon quantum dots, as a new member of the carbon nanomaterials family, can potentially be used as a highly promising visible-light-triggered antibacterial agent. In this work, the results of antibacterial and cytotoxic activities of gamma-ray-irradiated carbon quantum dots are presented. Carbon quantum dots (CQDs) were synthesized from citric acid by a pyrolysis procedure and irradiated by gamma rays at different doses (25, 50, 100 and 200 kGy). Structure, chemical composition and optical properties were investigated by atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, UV-Vis spectrometry and photoluminescence. Structural analysis showed that CQDs have a spherical-like shape and dose-dependent average diameters and heights. Antibacterial tests showed that all irradiated dots had antibacterial activity but CQDs irradiated with dose of 100 kGy had antibacterial activity against all seven pathogen-reference bacterial strains. Gamma-ray-modified CQDs did not show any cytotoxicity toward human fetal-originated MRC-5 cells. Moreover, fluorescence microscopy showed excellent cellular uptake of CQDs irradiated with doses of 25 and 200 kGy into MRC-5 cells.

Keywords: antibacterial activity; carbon quantum dots; cellular uptake; gamma rays.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Top view AFM images including particle size and height distributions of: (a) CQD_25, (b) CQD_50, (c) CQD_100 and (d) CQD_200 samples.
Figure 2
Figure 2
Fitted XPS spectra of (a) CQD_0, (b) CQD_25, (c) CQD_50, (d) CQD_100, (e) CQD_200 samples, (f) O/C ratio on sample surface as a function of irradiation dose. Peak C1 presents C-C/C-H bonds, peak C2 presents C-O/C-OH/C-O-C bonds, peak C3 presents C=O/O-C-O/CO3 bonds and peak C4 presents O=C-O bonds.
Figure 3
Figure 3
PL spectra of (a) CQD_0, (b) CQD_25, (c) CQD_50, (d) CQD_100 and (e) CQD_200 samples.
Figure 4
Figure 4
Photobleaching of ADBA under (a) ambient light (AL) and (b) blue light (BL) in the presence of all samples: CQD_0, CQD_25, CQD_50, CQD_100, CQD_200. All absorbance spectra of ABDA were recorded at 398 nm, normalized at the start of the irradiation, and averaged over several repeat experiments at a similar concentration of CQDs. Standard deviations for each measurement were smaller than the size of the symbols.
Figure 5
Figure 5
The bacterial growth change under CQDs compared between BL (blue dots) and AL (black dots) conditions. All tested bacteria, (a) MRSA, (b) S. aureus, (c) E. coli, (d) K. pneumonie, (e) P. mirabilis, (f) P. aeruginosa and (g) S. typhimurim, revealed some reduction in bacterial density under BL, but with CQD_100, all reductions were statistically significant. Note: as lower OD value means less bacterial growth and better antibacterial activity. Asterisks represent significant differences (* p < 0.05, ** p < 0.01, *** p < 0.001).
Figure 6
Figure 6
Top view AFM images of MRSA bacterial strains treated by CQD_100 samples under (a) AL and (b) BL irradiation.
Figure 7
Figure 7
Cytotoxity of CQD_25 and CQD_200 samples against MRC-5 cells. MRC-5 cells were treated for 24 h with increasing concentrations (1, 10, 25, 50, 75 and 100 µg/mL) of two tested CQD samples. Cell viability was expressed as the percentage of absorbance relative to the vehicle-control-treated MRC-5 cells for CQDs samples. Data are presented as the mean ± SD of at least three independent experiments. Asterisks indicate statistical significance (* p < 0.05). SD—standard deviation.
Figure 8
Figure 8
Cellular uptake of CQD_25 or CQD_200. Representative fluorescence images of (a) control MRC-5 cells (treated with vehicle control) and cells treated with 200 μg/mL of (b) CQD_25 and (c) CQD_200 for 48 h. Images were acquired at 20× magnification. Scale bar is 100 µm. Red arrows indicate MRC-5 cells with internalized irradiated CQDs samples.
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