Controlled 3D assembly and stimuli responsive behavior of DNA and peptide functionalized gold nanoparticles in solutions

DNA mediated directed self assembly of gold nanoparticles (AuNPs) has garnered immense interest due to its ability to precisely control supramolecular assemblies. Most experimental works have relied on utilizing the complementary interactions between the DNA strands to drive the self assembly of AuNPs grafted with DNA strands. In the present work, we have leveraged DNA-peptide interactions to tune the self assembly and stimuli responsive behavior of AuNPs grafted with single stranded DNA (ssDNA) and poly-l-lysine (PLL) chains. Our findings show that the electrostatic interactions between the negatively charged ssDNA grafts and positively charged PLL grafts, drive the self assembly of AuNPs of different sizes into 3D nanostructures. The transmission electron micrographs confirm that the smaller AuNPs grafted with PLL chains form a corona around the large AuNPs grafted with ssDNA like the petals around a flowery core to drive aggregation of large AuNPs. When the grafting of ssDNA and PLL on the different sized AuNPs is swapped, aggregates of large AuNPs mediated by the ssDNA grafts on the smaller AuNPs were observed. The presence of excess ssDNA/PLL chains in solutions affected both the morphology and the mechanism of aggregate formation. Coarse-grain molecular dynamics simulations qualitatively match the experimental findings and provided a scientific rationale to the above findings highlighting the role of chain entropy, molecular connectivity, and charge correlations on the self assembly of AuNPs.