Optical properties of novel synthesized ZrS₂ quantum dots based on Escherichia coli bacteria

There are a few reports on the synthesis of Zirconium disulfide quantum dots (ZrS₂ QDs) with complicated circumstances and no work has been reported about the biosynthesis of ZrS₂ QDs. In this work, a novel method of ZrS₂ QDs were successfully synthesized using  Escherichia coli ( E. coli ) bacteria. The E. coli bacteria was used for the degradation of L-cysteine to the sulfur ion (S^2-) to subsequent reaction with the ZrCl₄. The biosynthesis of ZrS₂ QDs was carried out during the stationary phase of the bacteria. The biosynthesized ZrS₂ QDs were characterized with techniques of XRD, DLS, FTIR, Raman spectroscopy, SEM and EDX. The antibacterial activity of the ZrS₂ QDs was tested against Gram-negative bacteria (E. coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus). The parameters of time, the concentration of L-cysteine and the concentration of ZrCl₄ that influenced on the fluorescence optical properties of the synthesized ZrS₂ QDs were studied with design-expert. The optimized conditions were obtained at the time of 60 min, concentrations of L-cysteine of 50 mM and concentrations of ZrCl₄ of 5 mM and it showed excellent optical fluorescence properties, with the intensity of 9102 and narrow band of full-width half maximum (FWHM) 45.5 nm. The best excitation wavelength (λ_ex) was obtained at 285 nm. The particle size of the synthesized ZrS₂ QDs was estimated by DLS and XRD methods, the average particle size was obtained 3.65 nm. Results shown a mutual affiliation between changing the particle size of the ZrS₂ QDs and its energy gap (E_g). The evolution biosynthesis time of ZrS₂ QDs was also investigated with UV-Vis and fluorescence spectroscopy methods. This work paves the way for further research into biosynthesis (use of bacteria or other microorganisms) of quantum dots that they are difficult to obtain with regular chemical methods.