Covalent functionalization of Ti3C2T MXene flakes with Gd-DTPA complex for stable and biocompatible MRI contrast agent

• The covalent functionalization of MXene with diethylenetriaminepentaacetic acid was proposed. • MXene-DTPA complexing with Gd 3+ provided paramagnetic response to the diamagnetic MXene. • MXene-Gd showed T 1 -MR imaging activity. • MXene-Gd showed oxidative resistance in phosphate buffer saline and blood serum. • The chelation of Gd 3+ ions by MXene-DTPA prevented leaking to bioliquids. MXenes are an excellent candidate for medical applications, including diagnostic approaches such as positron emission tomography, computed tomography, and magnetic resonance imaging (MRI). However, the utilization of MXenes for bioimaging is restricted by their commonly diamagnetic nature. MXenes can be functionalized using ferromagnetic or paramagnetic compounds and nanoparticles to develop efficient bioimaging tools. In contrast to previously published approaches based on electrostatic interactions, covalent approaches could enhance MXene stability and prevent self-aggregation with degradation. This work proposes covalent functionalization of Ti 3 C 2 T flakes with a chelating agent diethylenetriaminepentaacetic acid (DTPA) and further complexing with Gd 3+ ions. The developed functionalization procedure provides a paramagnetic response to the intrinsically diamagnetic Ti 3 C 2 T flakes for T 1 -MR imaging. Moreover, we observed the apparent dependency of magnetic relaxation time on the flake concentration, which enabled us to estimate the spatially resolved flake distribution. The covalent decoration strategy for MXene led to surface protection against oxidation in phosphate buffer saline and blood serum, accompanied by increased cytocompatibility. Moreover, chelation of Gd 3+ ions prevented leaking compared with electrostatic chemisorption. We demonstrated a high degree of photothermal conversion efficiency of MXene-Gd, anticipating future application in photothermal therapy. This work broadens the bioapplication of MXenes, not only by introducing an MRI contrast but also by developing covalent functionalization strategies for MXenes.