Lycopersicon esculentum leaf-extract was utilized in the synthesis of zinc-oxide nanoparticles (Le-ZnO-NPs) using zinc acetate as the precursor. The synthesized ZnO-NPs were attested by the detection of a notable absorption peak at 343 nm, appearing in UV–Vis spectra due to surface-plasmon-resonance. The XRD-spectrum recorded at 2θ values coincides with that of lattice planes. HR-TEM results revealed that Le-ZnO-NPs exhibited a crystalline structure with hexagonal wurtzite shape (10–50 nm size). The effectiveness of inhibition of the microbial biofilms of Proteus vulgaris, Enterococcus faecalis and Candida albicans was analyzed at a concentration of 100 µg ml−1. Moreover, Le-ZnO-NPs showed a significant range of anti-coagulant activity, in contrast to commercial anti-coagulant (heparin). Cytotoxicity studies showed that Le-ZnO-NPs (100 µg ml−1) are non-toxic to murine macrophage cells, but toxic to human cervical cancer (HeLa) cells. Indeed, a reduction in the viability of HeLa-cells and a notable variation in the apoptotic cell structure were apparent. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.