Cationic comb-type copolymer promotes DNA assembly on gold nanoparticles while enhancing particle dispersibility

Abstract

We previously reported that graft copolymers comprised of a cationic backbone and abundant grafts of hydrophilic dextran formed soluble interpolyelectrolyte complexes with anionic biopolymers and facilitated self-assembly and folding of the biopolymers, such as duplex formation of DNA and helical folding of a peptide. In this study, effects of the cationic graft copolymers on assembly of gold nanoparticles (AuNPs) and that of DNA on AuNPs were explored. While polylysine homopolymer caused aggregation of AuNP, the graft copolymer did not induce the aggregation as monitored by adsorption spectra. The highly-grafted copolymer at nano molar concentration was capable of suppressing AuNP aggregation induced by 3 M NaCl. Moreover, the copolymer did not cause aggregation of AuNPs whose surface were modified with oligonucleotides (ODN) having highly negative charges. In the presence of copolymer, melting temperature of DNA duplex formed between AuNP-ODN and its complementary ODN was increased about 10 °C, indicating that the copolymer enhanced stability of DNA duplex on the surface of AuNPs. It was concluded that the copolymer selectively promoted assembly of negatively charged DNA but inhibited aggregation of negatively charged AuNPs.