Crucial cytotoxic and antimicrobial activity changes driven by amount of doped silver in biocompatible carbon nitride nanosheets

[Display omitted] •Complex evaluation of biocompatibility of g-C3N4 before and after Ag modification.•Effective and simple preparation of Ag/g-C3N4 with desired amount of Ag NPs.•Thorough cytotoxicity tests by using five different human cell lines.•Importance of interference controls in interpretation of cytotoxicity results.•Useful insights for optimal properties of human-safe antimicrobial agents. The use of Ag-modified nanomaterials continues to attract attention in biological contamination control, their potential cytotoxicity is often overlooked. Herein, biocompatible carbon nitride is modified with 1 and 5 wt.% Ag and effects of different nanomaterial dose and Ag content on antimicrobial activity and cytotoxicity is studied. Pure Ag nanoparticles and AgNO3 is tested for comparison, together with ten bacterial strains including pan-resistant Pseudomonas aeruginosa. Cytotoxicity is then investigated in three adherent and two suspension human cell lines, and results confirm that cancer adherent cell lines are the most immune lines and human cervical adenocarcinoma cells (HeLa) are more resilient than human lung adenocarcinoma cells (A549). The HeLa remains over 90 % viable even after 24 -h treatment with the highest concentration of 5%Ag/g-C3N4 (300 mg L−1) while A549 sustained viability only up to 100 mg L−1. Higher concentrations then induce cytotoxicity and A549 cell viability decreases. Our results show the importance of complementary testing of cytotoxicity by LIVE/DEAD assay using flow cytometry with more different human cell lines, which might be less immune to tested nanomaterials than HeLa and A549. Combined controls of new antibacterial agent activity tests then provide increased knowledge of their biocompatibility.