Design of halloysite nanotube-based nanomaterials for theranostic applications: fluorescent probes and chemodynamic activity

The development of theranostic systems is of fundamental importance for the treatment of diseases. These systems should combine the features of fluorescent molecules that can act as diagnostic systems and species with therapeutic potential. Herein, we report the synthesis of a multifunctional halloysite nanotube (HNT)-based nanomaterial via the covalent modification of the external surface of the clay with a halochromic probe and the immobilization of Fe3O4 nanoparticles (HNTs-1@Fe3O4) with chemodynamic activity. The covalent modification of HNTs was performed using two different synthetic approaches, and the best strategy was evaluated by estimating the degree of functionalization of the clay via thermogravimetric analysis. The synthesized nanomaterial was thoroughly characterized, and its photoluminescence properties under different conditions, i.e. different solvents, pH conditions and temperatures, were studied. The HNTs-1@Fe3O4 nanomaterial was found to exhibit good peroxidase-like activity, as shown by testing its performance in the catalytic oxidation of the colorless enzyme substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to blue TMB oxide (ox-TMB) in the presence of H2O2. This study highlights the usefulness of the covalent approach for modifying halloysite surfaces to generate nanomaterials for potential tissue imaging under different stimuli. In addition, the combination with Fe3O4NPs led to the synthesis of multifunctional materials with potential use as theranostic systems for the treatment of diseases.