Bioactive potential of Helianthus annuus -derived ZnO nanoparticles: antibacterial, anti-biofilm, and thermal stability for dental materials

Antimicrobial resistance and biofilm-associated infections present persistent challenges in dentistry. This study investigated the plant-assisted synthesis and preliminary antibacterial properties of zinc oxide nanoparticles (ZnO NPs) prepared using waste Helianthus annuus stem-fibre extract. X-ray diffraction confirmed a predominantly crystalline hexagonal wurtzite ZnO phase, with a crystalline fraction of 69.6% and an apparent crystallite size of 27.35 ± 2.45 nm. FE-SEM revealed rod-like structures with mean length and width values of 384 ± 32 and 89 ± 5 nm, respectively, while EDX confirmed the presence of Zn and O in the analyzed region. At 200 µg mL−1 (20 µg per well), the nanoparticles produced inhibition zones of 32 ± 1 mm against Streptococcus mutans and 34 ± 1 mm against Escherichia coli. Streptomycin was included only as a positive assay control because differences in active mass and agar-diffusion behaviour precluded direct potency comparison. AO/PI-stained confocal images qualitatively indicated an increased proportion of membrane-compromised biofilm-associated cells following nanoparticle treatment. TGA under nitrogen showed multistage mass loss and a ZnO-rich residual fraction of 49% at 800 °C. This study was limited by testing only two bacterial strains, qualitative biofilm assessment, single-field SEM measurements, and the absence of cytotoxicity, ion-release, and dental-material incorporation studies.