Biosynthesis and characterization of transition metal sulfide quantum dots (MnS, FeS and ZnS QDs) with gram-positive and gram-negative bacteria and their optical studies

This is the first report on the biosynthesis of transition metal sulfide quantum dots (TMS QDs), including manganese sulfide (MnS), iron sulfide (FeS) and zinc sulfide (ZnS), using seven different bacterial strains encompassing both Gram-positive and Gram-negative bacteria. Over 21 different kinds of QD were synthesized and their optical properties were studied using fluorescence spectroscopy and UV–Vis spectrophotometry techniques. The MnS QDs, FeS QDs and ZnS QDs were synthesized via Bacillus subtilis , Pseudomonas aeruginosa and Staphylococcus aureus, respectively and characterized using FT-IR, XRD, DLS, SEM and EDX techniques. Also, the antibacterial activity of the MnS QDs, FeS QDs and ZnS QDs were tested against Gram-negative bacteria ( Escherichia coli ), Gram-positive bacteria ( Enterococcus faecalis ) and the foregoing producing bacteria. All fluorescence spectra of QDs were recorded at the optimal excitation wavelength (λ ex ) of 290 nm for all QDs. The band gap energies (E g ) of the QDs were calculated using Tauc plots. The biosynthesized QDs exhibited remarkable quantum efficiencies, the quantum yields of FeS QDs, MnS QDs and ZnS QDs were found to be 99.8 %, 98.2 % and 95.3 %, respectively. The XRD and DLS techniques were applied to analyze the size of biosynthesized QDs. Results showed the size of particles less than 10 nm, confirming the nanometric dimensions of the synthesized QDs. • For the first time, MnS, FeS, and ZnS quantum dots (QDs) were successfully synthesized using seven different bacterial strains (both Gram-positive and Gram-negative). • The biosynthesized QDs exhibited remarkable quantum efficiencies: FeS QDs reached near-perfect efficiency (99.8 %), while MnS and ZnS QDs showed exceptional yields of 98.2 % and 95.3 %, respectively. • UV–Vis analysis and Tauc plots confirmed size-dependent bandgap energies (Size-Dependent Properties). • XRD, FTIR, DLS, SEM, and EDX analyses confirmed the nanometric dimensions, crystalline structures, and elemental purity of the biosynthesized QDs, validating their successful formation.