Mixed Quaternary-Ammonium-Coated Gold Nanoparticles for Delivery of MicroRNA

The research described in this dissertation seeks to develop an inorganic transfection delivery carrier using a custom-designed self-assembled monolayer (SAM). Initial studies describe the preparation of SAMs on flat gold surfaces derived from three unique bidentate adsorbates and two analogous monodentate adsorbates of different chain lengths bearing a quaternary-ammonium terminal group. The generated SAMs were evaluated using ellipsometry, X-ray photoelectron spectroscopy (XPS), contact angle goniometry, polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and electrochemical quartz crystal microbalance (eQCM). The effect of the packing density of the SAMs on oligonucleotide binding was evaluated in regards to the terminal group used. In an effort to enhance the immobilization of oligonucleotides on the SAMs surfaces, the use of a mixed monolayer containing a long and short-chained adsorbate was utilized. The SAM surface comprised of a 50:50 ratio was determined to have the greatest amount of immobilized oligonucleotides. To further expand on the initial study and to design a nanocarrier capable of initiating the "proton sponge" effect in cells, the quaternary-ammonium-terminated adsorbate was mixed with an ammonium-terminated adsorbate, both bearing a bidentate headgroup. The effect of burying either the quaternary-ammonium or ammonium moiety into the film on oligonucleotide loading was investigated. Based on our analysis, the SAM surface comprised of a 75:25 (ammonium: quaternary-ammonium) in which the quaternary ammonium species is buried resulted in the highest oligonucleotide loading. The development of a layer-by-layer gold nanoparticle complex for the delivery of miRNA was pursued using the 75:25 SAM surface. The nanocomplex provided a platform to electrostatically bind miRNA through its phosphate backbone. The uniquely designed layer-by-layer gold nanocomplex was characterized by dynamic light scattering (DLS), gel retardation assay, transmission electron microscope (TEM), ultraviolet visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), and zeta potential (ζ-potential). Furthermore, miRNA immobilized onto the gold nanocomplex was transfected into osteosarcoma (HOS) cell lines and then quantified by quantitative polymerase chain reaction (qPCR). The cytotoxicity of the nanocomplex was then examined by MTS assay. Overall, the gold nanocomplex was successfully developed and shown to have low toxicity while delivering miRNA into an HOS cell line with a 10,000-fold increase.