Photothermal performance of Nb2CTx and Ti3C2Tx MXenes for antibacterial and in vitro cytotoxicity

Photothermal therapy (PTT) has emerged as a noninvasive strategy for treating cancer and infectious diseases through near-infrared (NIR)-induced localized hyperthermia. MXenes, a family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, have recently attracted considerable attention owing to their ultrahigh photothermal conversion efficiency. Herein, Nb2CTx and Ti3C2Tx were synthesized via hydrothermal and MILD methods, respectively. Their crystallinity and thermal stability were evaluated using X-ray diffraction (XRD) and thermogravimetric analysis (TGA). UV-Vis-NIR spectroscopy confirmed strong NIR absorption. In addition, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) verified the formation of exfoliated and delaminated MXene nanosheets. Hydrodynamic diameter of 301.9 nm and zeta potential of -32.44 mV were determined for Nb2CTx which was larger and more negative compared to Ti3C2Tx with size of 178.2 nm and zeta potential of -26.69 mV. A higher photothermal conversion efficiency (η) of 84.12% was determined for Ti3C2Tx compared with 66.69% for Nb2CTx. The antibacterial activity of both MXenes showed a dose-dependent effect against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), while Ti3C2Tx exhibited stronger antibacterial performance. Under NIR irradiation, the minimum inhibitory concentration (MIC) value of both MXenes decreased by twofold, indicating enhanced photothermal antibacterial performance. Under dark conditions, both MXenes showed limited cytotoxicity toward normal cells up to 200 µg/mL, while Ti3C2Tx exhibited pronounced cytotoxicity against human breast cancer MCF-7 cells, which was further enhanced under NIR irradiation. Overall, these findings characterize the NIR-responsive antibacterial activity and in vitro cytotoxicity of Ti3C2Tx and Nb2CTx, providing a basis for further evaluation of their biomedical applicability.