Different chemical strategies to aminate oxidised multi-walled carbon nanotubes for siRNA complexation and delivery

In this work, we have investigated the preparation of amino-functionalised multi-walled carbon nanotubes (MWCNTs) as potential carriers for the delivery of siRNA. Several studies have shown promising results exploiting functionalised CNTs for the delivery of genetic material in vitro and in vivo. Our groups have previously observed that the type of surface functionalisation used to modify oxidised MWCNTs (oxMWCNTs) can lead to significant differences in nanotube cellular uptake and delivery capability. In those studies, amino-functionalised CNTs were obtained by cycloaddition reactions. Here, we focused on the direct conversion of the carboxylic groups present on oxMWCNTs into amines, and we attempted different synthetic strategies in order to directly tether the amines onto the CNTs, without extending the lateral chain. The functionalised material was characterised by X-ray photoelectron spectroscopy, Fourier transform infra-red spectroscopy and transmission electron microscopy, and the most water-dispersible CNTs were selected for siRNA complexation and cellular uptake studies. The aminated conjugates are demonstrated to be promising vectors to achieve intracellular transport of genetic information.