Fabrication and cytotoxicity evaluation of polyethyleneimine conjugated fluorescent MXene nanosheets as cancer theranostics agent

MXene has become one of the most sought-after 2D materials with incredible potential in various fields. This work reports the use of a cationic polymer polyethyleneimine (PEI) to generate a positive charge on the MXene surface. PEI is a positively charged polymer containing repeating amine groups. PEI functionalized MXene nanoflakes (PEI_Ti3C2) were produced by etching Ti3AlC2, followed by ultrasonication along with PEI, and then hydrothermally treated at 200 °C for 24 h. The as-obtained nanosheets were characterized through XRD, AFM, TEM, UV–Vis spectroscopy, PL, and FTIR. The thickness of PEI_Ti3C2 was found to be 2.6 ± 0.8 nm compared to control (h-Ti3C2) which exhibited 6.8 ± 1.6 nm height, proving utilization of PEI both as a surfactant as well as a functionalizing agent. The surface charge of PEI_Ti3C2 sheets was observed to be 15.57 ± 2.76 mV due to the presence of imine groups. Colloidal solution of PEI_Ti3C2 displayed high absorption in both the UV (315–600 nm) and NIR ranges (880–996 nm) as well as exhibits blue fluorescence. The use of the PEI polymer also assists in MXene forming a stable aqueous dispersion. PEI_Ti3C2 showed high biocompatibility in mouse fibroblast and red blood cells. On the other hand, the nanosheets demonstrated concentration-dependent cellular toxicity on cancer cells when irradiated with 808 nm laser irradiation for 10 min. The small-sized PEI_Ti3C2 are highly scalable, reproducible, biocompatible, possess intrinsic NIR activity, fluorescence, and cationic character. The NIR activity and photoluminescence of the 2D nanosheets make them multifaceted to be utilized as cell labeling probes, sensors, and photothermal therapy.