Mechanistic Investigation into the Effect of Different DNA Sequences on the Shape and Morphology of Nanoparticles

Controlling the shape and size of noble metal nanoparticles such as Ag, Au, Pt, and Pd enables the fine tuning of their inherent physical and chemical properties. This translates to the more efficient use of these materials for various applications, including electrochemistry. The ligand environment during the synthesis of metal nanoparticles often plays an important role by influencing the rates of precursor reduction and providing facet stabilization. Our lab has explored the use of DNA as a ligand in nanomaterial synthesis extending the function of DNA beyond its traditional role as a genetic material.¹ Given DNA’s excellent sequence programmability with the four bases cytosine (C), guanine (G), adenine (A) and thymine (T) and its ease of chemical modification, DNA can serve as an ideal candidate for nanoparticle shape control. Recently we have demonstrated successfully that DNA can be used as a ligand for shape control of gold and silver nanoparticles.²We have also expanded the scope of DNA mediated shape control into bimetallic nanoparticle systems.

The use of programmed DNA oligomers on the growth of gold nanoprisms has resulted in interesting shapes such as rough round, six-pointed star, hexagon and smooth round shapes respectively, for A, T, G and C. Despite the interesting finding, the mechanism of DNA mediated growth remains unclear. Our goal in this work focuses on elucidating the role of DNA using spectroscopic and microscopic characterization of particle growth kinetics. Using oligomers of thymine, the seed nanoprism grew into six point stars. The shape was observed to proceed through intermediates- from a prism, to a round polyhedron, to a hexagon and finally into a six pointed star. The intermediates observed from this growth were observed with other bases as well. Round polyhedron shapes were observed for polyadenine and polycytosine, and hexagon shapes for polyguanine. The extent of growth formed using different bases was found to be correlated to the trend of binding affinity of the bases to gold surfaces (A>C>G>T). This hypothesis is supported using zeta potential and fluorescence assays to quantify the DNA on the nanoparticles. The role of DNA binding to the nanoprism seed and the gold precursor in guiding the nanoparticle growth is proposed. The relationship between the amount of DNA and gold precursor used for the growth was also determined.

1. Tan, L. H.; Xing, H.; Lu, Y., DNA as a Powerful Tool for Morphology Control, Spatial Positioning, and Dynamic Assembly of Nanoparticles. Acc. Chem. Res. 2014, 47(6), 1881-1890.

2. (a) Wu, J.; Tan, L. H.; Hwang, K.; Xing, H.; Wu, P.; Li, W.; Lu, Y., DNA Sequence-Dependent Morphological Evolution of Silver Nanoparticles and Their Optical and Hybridization Properties. J. Am. Chem. Soc. 2014, 136 (43), 15195-15202; (b) Wang, Z.; Tang, L.; Tan, L. H.; Li, J.; Lu, Y., Discovery of the DNA “Genetic Code” for Abiological Gold Nanoparticle Morphologies. Angew. Chem. Int. Ed. 2012, 51 (36), 9078-9082; (c) Wang, Z.; Zhang, J.; Ekman, J. M.; Kenis, P. J. A.; Lu, Y., DNA-Mediated Control of Metal Nanoparticle Shape: One-Pot Synthesis and Cellular Uptake of Highly Stable and Functional Gold Nanoflowers. Nano Lett. 2010, 10 (5), 1886-1891.