Site-specific halloysite functionalization by polydopamine: A new synthetic route for potential near infrared-activated delivery system

Halloysite nanotubes (HNTs) represent a versatile core structure for the design of functional nanosystemsof biomedical interest. However, the development of selective methodologies for the site-controlled functionalizationof the nanotubes at specific sites is not an easy task. This study aims to accomplish a procedurefor the site-selective/specific, ''pin-point", functionalization of HNTs with polydopamine(HNTs@PDA). This goal was achieved, at pH 6.5, by exploiting the basicity of ZnO nanoparticles anchoredon the HNTs external surface (HNTs@ZnO) to induce a punctual polydopamine polymerization and coating.The morphology and the chemical composition of the nanomaterial was demonstrated by severaltechniques. Turbidimetric analysis showed that PDA coating affected the aqueous stability ofHNTs@PDA compared to both HNTs@ZnO and HNTs. Notably, hyperthermia studies revealed that thenanomaterial induced a local thermic rise, up to 50 C, under near-infrared (NIR) irradiation.