Solution-phase synthesis of peptide-functionalized metallic nanoparticles and chalcogenide semiconductor nanocrystals
Over the past two decades, the field of nanotechnology and its applications have developed at an extraordinary pace. The small size (1-100 nm) and high surface area of nanomaterials give rise to novel chemical and physical properties that enable numerous applications in electronics, optics, energy harvesting, and medicine. Research on nanomaterial assemblies is of particular interest, because such assemblies can exhibit emergent behavior of the assembly as a whole, in addition to the properties of the constituent nanomaterials. Numerous research efforts have been focused on this area, especially in the case of dynamic nanostructure assemblies, due to their novel optical, electronic, and magnetic properties. Bio-nanocombinatorics, defined as the controlled assembly of nanomaterials using biomolecular interactions, is an emerging approach in this field. Nanomaterial assembly directed using complementary DNA molecules is the most intensively studied area in this field. However, this approach suffers from a lack of diversity in the inorganic components due to low degree of assembly control with the use of non-specific DNA linkers. In contrast, short peptides identified for their specific recognition and binding to inorganic materials hold promise to open up new avenues to creation of dynamic nanomaterial assemblies due to their high degree of specificity and selectivity. Metallic nanomaterials, especially gold and silver nanomaterials, have been widely studied due to their localized surface plasmon resonance (LSPR). The conjugation of gold and silver nanoparticles with biomolecules is a promising approach to their assembly and can enable their use in applications such as biosensing. To this end, in chapters 2-6 of this dissertation, we demonstrate the synthesis of various metallic nanostructures using peptides that were previously screened for their binding affinities toward specific inorganic surfaces. We found that the morphology, size, aggregation state, surface structure, and resulting optical and catalytic properties of these nanostructures were governed by many factors, particularly by peptide sequence, binding affinity (including both enthalpic and entropic components), molecular conformation, molecular reconfigurability (static or dynamic), and reaction conditions. Moreover, group IV-VI and V-VI colloidal nanocrystals (NCs) are a group of nanomaterials that have been widely investigated for their potential applications ranging from optoelectronic and electronic devices, to biomedicine. Colloidal NCs of group IV-VI semiconductors, including tin and lead chalcogenides, are of great interest for applications in solution-processed photovoltaic and optoelectronic devices due to their narrow band gaps and potential to be used in near-infrared (NIR) and infrared (IR) photodetectors and photovoltaic devices. Tin is an earth abundant and low toxicity element compared with lead or cadmium. Thus, tin chalcogenide NCs can be a promising candidate for low-cost, environmentally benign photovoltaic and optoelectronic materials. In addition, group V-VI chalcogenide NCs are of interest due to their promising applications in thermoelectric (TE) and photovoltaic (PV) devices. In this regard, chapter 7 of this dissertation focuses on the synthesis of tin chalcogenides, lead tin sulfide alloys, and antimony selenide nanocrystals with various compositions, sizes, and morphologies.