Salt enhanced sedimentation of halloysite nanotubes for precise determination of DNA adsorption isotherm

The controversy about the adsorption of DNA onto/into halloysite is mainly due to the lacking of an absorption isotherm. As in other colloidal clays systems, experimental difficulties in separating excess non-adsorbed DNA from DNA-halloysite hybrids hinder the reliable determination of the adsorption. According to literature, sedimentation of nanoparticles in a colloidal system is affected by a complex interplay of local density, viscosity and inter-particle interactions. In this context, an increase in the ionic strength can enhance sedimentation by reducing inter-particle repulsions. In this work, we propose an improved centrifugation procedure by fine tuning of the ionic strength An effective strategy for sedimentation of DNA-halloysite hybrids is defined and discussed. Adsorption isotherms are obtained for chromosomal linear DNA in both native or denatured conditions. Importantly, DNA is adsorbed at the outer surface of halloysite despite electrostatic repulsive interactions. The proposed method will boost investigations on the adsorption of a variety nucleic acids for gene delivery formulation or the mechanistic understanding of biological impact of halloysite nanotubes and other novel nanomaterials.