Spectrophotometric and nucleic acid-binding properties of halloysite clay nanotubes and kaolinite

Halloysite particles (HNTs) are naturally occurring aluminosilicate nanotubes of low toxicity that have shown great promise for drug and biomolecule delivery into human and animal cells. Kaolinite particles retain the same layered structure as HNT, but do not form nanotubes. In this study, the spectrophotometric and sedimentation properties of the two clays in aqueous solutions and their abilities to associate with both small and large nucleic acids have been investigated. Both clays scattered ultraviolet light strongly and this characteristic of HNT was not affected by either vacuum treatment to remove trapped gases or by sonication. Vacuum treatment increased the binding of small nucleic acids to HNT and this association was further enhanced by addition of divalent metal ions. By contrast, only small RNAs were bound efficiently by kaolinite in the presence of Mg2+ ions. Large linear double-stranded DNAs and circular plasmid DNAs bound poorly to kaolinite under all conditions, but these nucleic acids could form strong associations with HNT. Differences in binding data were largely consistent with measurements of the available surface areas of each clay. These results demonstrate that interactions with each clay are critically dependent on both the type and the conformation of each nucleic acid.

Automated summary

This study investigates the spectrophotometric and sedimentation properties of two clays in aqueous solutions and their abilities to bind with small and large nucleic acids. The results show that HNT has strong binding capabilities for small nucleic acids, while kaolinite only binds efficiently with small nucleic acids in the presence of Mg2+ ions. Large linear double-stranded DNAs and circular plasmid DNAs have poor binding with kaolinite but can strongly associate with HNT. These findings demonstrate that the interactions between clays and nucleic acids depend on the type and conformation of each nucleic acid.