Green synthesis of ZnO nanoparticles and biological applications as broad-spectrum bactericidal, antibiofilm effects and biocompatibility studies on Zebrafish embryo

This work generated zinc oxide nanoparticles (ZnO NPs) using Ocimum tenuiflorum in an inexpensive and environmentally friendly manner. The generated ZnO NPs were analysed using Ultra visible spectroscopy (UV–Vis), Fourier transformed infrared spectroscopy (FTIR), Scanning electron microscopy-Energy X-ray diffraction spectroscopy (SEM-EDX), Transmission electron microscopy (TEM), and X-ray diffraction (XRD). Bio-synthesized ZnO NPs showed UV–Visible absorbance maxima at 290 nm, indicating bio reduction and stability. The DRS spectra revealed a straight band gap value of 3.24 eV. Alcohols, alkanes, phenols, and amines in FTIR may contain reduced and capped zinc ions. Crystalline ZnO nanoparticles were verified by XRD. Biosynthesized ZnO NPs were exhibited in spherical and 5–35.49 nm in size by FESEM and TEM. EDX confirmed NPs zinc elemental signatures. Antibacterial properties showed that ZnO NPs effectively inhibited gram (+ve) and gram (−ve) pathogens, including E. coli (20.0 ± 0.8 mm), E. faecalis (20.0 ± 0.5 mm), S. aureus (18.01 ± 1.2 mm), and S. mutans (17.5 ± 1.0 mm). This study shows that biosynthesized ZnO NPs inhibit biofilm growth by 0.198–1.431 O.D values (Optical density). Antibiofilm inhibition was concentration-dependent. Nanoparticles proved effective against E. coli, S. mutans, S. aureus, and E. faecalis with MICs of 15 and 25 µg/mL. Time-dependent death kinetic studies indicated that 8–12 h ZnO NPs killed all bacteria. Also, ZnO NPs had low harmful effects on zebrafish eggs at doses upto 1 mg/mL. In summary, the production of green ZnO NPs offers a sustainable and biocompatible approach that is well-suited for various biological applications.