Size-Dependent in Vitro Biocompatibility and Uptake Process of Polymeric Carbon Nitride

Polymeric carbon nitride (PCN), which demonstrates unique properties, has been widely explored, mostly in photocatalysis; however, the evaluation of its biocompatibility is still needed. Herein, the cytocompatibility of PCN with different lateral size distributions (A-PCN with 160 nm, B-PCN with 20 nm, and C-PCN with 10 nm dominating lateral sizes) was investigated. The viability of three cell lines (L929, MCF-7, and HepG2) has been determined using cell counting kit-8 (CCK-8), neutral red uptake (NRU), and lactate dehydrogenase (LDH) leakage assays. It was found that the highest cytotoxicity of PCN was observed for flakes with a lateral size of similar to 20 nm (B-PCN) in three cell lines after 48 h of exposition. The uptake process of B-PCN sheets labeled with fluorescein isothiocyanate (FITC) by cells was also the most effective. Confocal laser scanning microscopy and atomic force microscopy revealed the nanomaterial distribution throughout the cytoplasm and perinuclear region. The results demonstrated the correlation among size, internalization process, and cytocompatibility of the tested polymeric carbon nitride structures.