Date on Master's Thesis/Doctoral Dissertation
Committee Co-Chair (if applicable)
Asymmetric functionalization; DNA-induced assembly; Surface-enhanced spectroscopy; Fano resonance; Hierarchical organization of nanocrystals; Polymer bead-nanoparticle conjugates
Colloidal Janus particles that possess more than one type of surface chemistry or functionalities have drawn significant interest due to their enormous potential in bottom-up synthetic strategies for complex superstructures. Moreover, the property of molecular recognition, tunability, and predictability of the DNA-mediated interactions enable a high degree of control over particle assembly to generate highly ordered nanostructures with emergent applications. In this dissertation, we present our works on the synthesis of Janus particles from anisotropic gold nanoprisms, and DNA- mediated assembly of nanoprisms and polymer beads in four major areas: 1) Facet selective asymmetric functionalization of gold nanoprisms for Janus particle synthesis, 2) Synthesis and plasmonic properties of nanoprism dimers and trimers, 3) DNA mediated hierarchical organization of gold nanoprisms into 3D superlattices and their application in Surface-enhanced Raman scattering (SERS) and Fluorescence, and 4) DNA induced assembly of nanoprisms and polystyrene beads into 3D SERS substrates. The first set of Janus particles, consisting of gold nanoprisms coated with hexadecane and DNA dynamically align themselves at the interface of a water-chloroform mixture. The Janus character of a second set of Janus particles functionalized with PEG and DNA is confirmed by the selective attachment of gold nanoparticles to the DNA-containing facets of Janus nanoprisms. The presence of two mutually exclusive coatings on the opposite major facets of nanoprisms allows the formation of nanoprisms dimers and trimers, which exhibit distinctly different plasmonic properties from their monomer counterparts. Furthermore, anisotropic nanoparticles associate in a manner that ensures maximum hybridization interactions. DNA-induced and shape directed face-to-face assembly of anisotropic gold nanoprisms leads to the formation of nanoprism 1D stacks, which are then assembled into 3D nanoprism superlattices using a near-Tm thermal annealing approach that promotes long-range DNA-induced interaction and ordering. Finally, we fabricate a large area SERS substrate via a two-step DNA mediated assembly of gold nanoprisms and polystyrene beads into a large ensemble of beads, which consist of 20-50 nanoprism-coated beads. An excellent enhancement factor (EF) of 1.09×10^5 and a very high detection sensitivity (up to 10-10 M) are observed for the analysis of a probe molecule (Methylene blue) using the SERS substrate.
Chowdhury, Md. Emtias, "Design, synthesis and application of Janus gold nanoprisms for directed self-assembly." (2020). Electronic Theses and Dissertations. Paper 3539.