Investigation of the biological activities of a polyethyleneimine-Schiff base functionalized nitrogen-doped graphene quantum dot and silver nanocomposite

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The biological activities of original 5-methylsalicylaldehyde-polyethyleneimine Schiff base functionalized nitrogen-doped graphene quantum dot (5-MESAL-PEI N-GQD) and its silver nanocomposite (AgNP/5-MESAL-PEI N-GQD) were investigated. 5-MESAL-PEI N-GQD and AgNP/5-MESAL-PEI N-GQD were characterized using Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Transmission Electron Microscopy (TEM). DNA-binding interactions were evaluated using Calf Thymus - Deoxyribonucleic Acid (CT-DNA) via UV-Vis absorption spectroscopy, while DNA cleavage activity was analyzed by agarose gel electrophoresis using pBR322 plasmid DNA. The antimicrobial activity was assessed by determining the minimum inhibitory concentration (MIC) against various bacterial and yeast strains. Antibiofilm activity was evaluated through the microplate assay using different microbial strains. Antioxidant properties were investigated by 1,1-diphenyl-2picryhydrazyl (DPPH) radical scavenging activity, 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging assay, and ferric reducing antioxidant power (FRAP) assay. As a result, both 5-MESAL-PEI N-GQD and AgNP/5-MESAL-PEI N-GQD exhibited electrostatic interactions with CT-DNA and were found to induce both hydrolytic and oxidative cleavage of supercoiled pBR322 plasmid DNA in a concentration-dependent manner. AgNP/5-MESAL-PEI N-GQD was demonstrated higher antimicrobial activity compared to 5-MESAL-PEI N-GQD. Furthermore, both compounds exhibited strong antibiofilm effects against the tested microbial strains. As a conclusion, the antibacterial, antibiofilm, antioxidant, and DNA interaction properties of these nanomaterials suggest that they could serve as promising bioactive agents for both biotechnological and clinical applications.