Tuning Self-Assembled Gold Nanoparticle Homodimer Structures for Fluorescence Enhancement

Abstract

Gold nanospheres (Au NPs) are valuable nanotechnology building blocks as their unique electronic properties are size- and shape- dependent. Such nanoparticles exhibit a localized surface plasmon resonance (LSPR), which gives their characteristic red spectral emission and generates an electromagnetic field near the particle surface. One property as a result of the LSPR is field enhancement when two spheres are brought into close proximity with one another. This characteristic makes them useful as electronically active structures that can be used in applications such as increasing fluorescence emission. Previous experiments have sought to harness Au NP’s ability as self-assembled structures and optical antennas for fluorophore enhancement. However, the limits for maximizing conjunct plasmonic properties are unknown, and challenges in controlling the colloidal stability and purification resolution of large diameter spheres (80 nm) are still not widely explored. Here I report the creation of a dimer, composed of two 80 nm gold spheres connected via DNA, that controls a decrease in interparticle distance to increase electromagnetic field enhancement. Spheres labelled with one DNA strand are isolated using DNA affinity column chromatography, and one-pot self-assembly enables two species to complementary pair into a homodimer. I used UV-vis spectroscopy, gel electrophoresis and transmission electron microscopy techniques to confirm dimer formation. From these, field enhancement with my dimer is predicted to be greater than other comparable structures. The synthetic strategy of colloidal self-assembled gold dimer here suggests a more flexible way to capitalize on large diameter metallic building blocks and their plasmonic properties than has previously been reported.