Charge density and particle size effects on oligonucleotide and plasmid DNA binding to nanosized hydrotalcite

Hydrotalcite (HT) and other layered double metal hydroxides are of great interest as gene delivery and timed release drug delivery systems and as enteric vehicles for biologically active molecules that are sensitive to gastric fluids. HT is a naturally occurring double metal hydroxide that can be synthesized as a nanomaterial consisting of a brucite structure with isomorphous substitution of aluminum ions. These positively charged nanoparticles exhibit plate-like morphology with very high aspect ratios. Biomolecules such as nucleic acids and proteins form strong associations with HT because they can associate with the positively charged layers. The binding of nucleic acids with HT and other nanomaterials is currently being investigated for potential use in gene therapy; however, the binding of specific nucleic acid forms, such as single- and double-stranded DNA, has been little explored. In addition, the effects of charge density and particle size on DNA adsorption has not been studied. In this paper, the binding of different forms of DNA to a series of HTs prepared at different temperatures and with different anion exchange capacities has been investigated. Experiments demonstrated that HTs synthesized at higher temperatures associate with both single- and double-stranded oligomers and circular plasmid DNA more tightly than HTs synthesized at room temperature, likely due to the hydrothermal conditions promoting larger particle sizes. HT with an anion exchange capacity of 300 meq/100 g demonstrated the highest binding of DNA, likely due to the closer match of charge densities between the HT and DNA. The details of the interaction of various forms of DNA with HT as a function of charge density, particle size, and concentration are discussed.