Facile Synthesis of L-Cysteine Functionalized Graphene Quantum Dots as a Bioimaging and Photosensitive Agent

Abstract

Nowadays, a larger number of aggressive and corrosive chemical reagents as well as toxic solvents are used to achieve structural modification and cleaning of the final products. These lead to the production of residual, waste chemicals, which are often reactive, cancerogenic, and toxic to the environment. This study shows a new approach to the modification of graphene quantum dots (GQDs) using gamma irradiation where the usage of reagents was avoided. We achieved the incorporation of S and N atoms in the GQD structure by selecting an aqueous solution of L-cysteine as an irradiation medium. GQDs were exposed to gamma-irradiation at doses of 25, 50 and 200 kGy. After irradiation, the optical, structural, and morphological properties, as well as the possibility of their use as an agent in bioimaging and photodynamic therapy, were studied. We measured an enhanced quantum yield of photoluminescence with the highest dose of 25 kGy (21.60%). Both S- and N-functional groups were detected in all gamma-irradiated GQDs: amino, amide, thiol, and thione. Spin trap electron paramagnetic resonance showed that GQDs irradiated with 25 kGy can generate singlet oxygen upon illumination. Bioimaging on HeLa cells showed the best visibility for cells treated with GQDs irradiated with 25 kGy, while cytotoxicity was not detected after treatment of HeLa cells with gamma-irradiated GQDs.

Gamma-Ray-Induced Structural Transformation of GQDs towards the Improvement of Their Optical Properties, Monitoring of Selected Toxic Compounds, and Photo-Induced Effects on Bacterial Strains

“…The bands at 2970, about 2930, and 2870 cm −1 in pristine and irradiated GQDs are attributed to stretching vibrations of C-H bonds in -CH, and -CH 2 groups [ 35 ]. The band located at 1633 cm −1 in the spectra of all samples steams from stretching vibrations of C=O bonds in amide functional groups [ 22 ]. The high-intensity band at 1572 cm −1 detected in the spectrum of the p-GQDs is assigned to stretching vibrations of the C=C bonds in π-conjugated domains of GQDs [ 35 ].…”

“…The bands centered at 1330 cm −1 in the spectra of p-GQDs, and GQDs-EDA/5 g , at 1339 cm −1 in the spectra of GQDs-EDA/1 g and GQDs-EDA/10 g, as well as the high-intensity band at 1395 cm −1 found in all spectra, originate from vibrations of the C-OH bonds [ 40 , 41 ]. The bands at 1161 cm −1 observed in all spectra and the one around 1088 cm −1 found in the spectra of p-GQDs, GQD-EDA/1 g , and GQDs-EDA/10 g are assigned to asymmetric [ 42 ] and symmetric stretching vibrations of the C-O bonds in epoxy groups [ 22 , 43 ].…”

“…Later, He et al irradiated GO at a dose of 200 kGy in the presence of different EDA weight ratios (1:0, 1:5, 1:10, and 1:20) [ 21 ]. Milenković et al fabricated N,S-doped GQDs at irradiation doses from 25 to 200 kGy in the presence of isopropyl alcohol and L-cysteine as a source of heteroatoms [ 22 ]. After irradiation, PL QY was increased from 1.45 to 21.60% for GQDs irradiated at a dose of 25 kGy.…”

Preparation, Marriage Chemistry and Applications of Graphene Quantum Dots–Nanocellulose Composite: A Brief Review

“…As GQDs can significantly affect the properties of a composite, determining the GQD content threshold of a nanocomposite depends on its specific application, as different concentrations are required for different applications. The GQD, a functional derivative of graphene, consists of many oxygen-containing functional groups, such as ether, hydroxyl, carbonyl and carboxyl, on the edges and basal planes [92,93]. Despite the smaller size of GQDs, their edge sites are more reactive than the carbon matrix [94].…”

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

“…In the FTIR spectrum of GQDs synthesized by the electrochemical oxidation of graphite electrodes, one can observe a band at 3421 cm −1 that stems from the vibration of the O-H stretching mode in hydroxyl groups attached to carbon atoms [ 159 ]. Other bands located at 2970, 2930, and 2877 cm −1 correspond to vibrations of the C-H bond in hydrocarbon fragments.…”