Serial dilution bioassay for the detection of antibacterial potential of ZnSe quantum dots and their Fourier transform infra-red spectroscopy

Abstract

The aim of this work lies in synthesize of ZnSe nanoparticles (quantum dots: QDs) by microwave (MW) irradiation-assisted method; this method can provide the reduced-dimension particles having high quantum confinements. The Cu-doped and undoped ZnSe QDs were synthesized at the presence of mercaptoacetic acid (MAA) capping agent at different physical-chemical conditions of pH-end (8.0, 10.2, 11.2 and 12.2) of suspension solution, different MW irradiation times (MWIRT = 0, 1, 2, 3, 4 and 6 min) and also at different Cu concentrations (0, 0.1, 0.75, and 1.5 mol%); so, produced QDs were characterized structurally employing Fourier transform infra-red spectroscopy (FTIR) to complete previously published results on their X-ray diffraction (XRD) and UV–Visible spectroscopy. Also, serial dilution bioassay was performed against both gram positive and gram negative bacteria to assess their antibacterial activity; for the antibacterial experiments, four Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus cereus bacteria were used as test strains. Results show that these QDs are as potential and promising antibacterial agents, with a dominant (optimal) activity in the cases of (pH = 10.2, MWIRT = 0 min), (pH = 12.2, MWIRT = 0 min; and pH = 11.2, Cu dopant = 1.5%) and (pH = 11.2, MWIRT = 4 min) for Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus cereus, respectively. Minimum inhibitory concentration (MIC) results suggest them as novel class of bio-agents. The studied ZnSe QDs had a size of about ∼2 nm and MIC of about 3 ppm for all tested samples. All samples have the same minimum bactericidal concentration (MBC) as MIC, indicating both inhibition and killing of microorganisms. To draw inference about the prominent bio-activity of ZnSe QDs, they should be synthesized in nano-scale, in which effectively enable them to penetrate to the cell walls of both gram-negative and gram-positive bacteria. The FTIR absorption peaks for the synthesized samples, confirm the formation of ZnSe structure, justifying the previously reported results of XRD, field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX); so, the interaction between Se2− and Zn2+ ions were confirmed via FTIR analysis.