In the past few decades, one dimensional and two dimensional nanomaterials have attracted great interest in syntheses and applications because of their unusual mechanical, electrical, optical, catalytic and surface properties. Among the various types of noble metal nanomaterials, gold nanostructures are widely used for biosensor application due to their physicochemical properties, biocompatibility and relatively simple production and modification. In particular, atomically flat and ultraclean Au nanostructures are regarded as the best materials for bioactive surfaces to be form high-quality self-assembled monolayers (SAMs).
Silver chalcogenides are also promising photoelectric, thermoelectric and intrinsic semiconductor materials with a narrow band gap in the various type of semimetal nanomaterials. A recent theoretical study suggested that silver chlacogenides such as $Ag_2Te$, $Ag_2Se$ are topological insulator with a high anisotropic Dirac cone. The single crystalline silver chalcogenide nanostructures offer attractive system to study unique properties of strong spin-orbit coupling materials because of their large surface to volume ratio and quantum confinement effect. In this dissertation, we present the works on Au nanostructures based Surface-enhanced Raman scattering (SERS) sensors for biosensor application and β-$Ag_2Se$ nanowire device for electronic material application. The single-crystalline Au nanostructures and β-$Ag_2Se$ nanostructures synthesized in vapor phase have atomically smooth and ultraclean surface. The use of these Au nanostructures is highly advantageous for the SERS based detection of biomolecules because their well-defined geometric architecture provides reliable SERS signals and supply good substrate to immobilize biomolecules uniformly without surface hindrance. The synthesized β-$Ag_2Se$ nanostructures by CVD method provide the advantage of transport measurement because of their surface cleanness and single crystallinity. This thesis is organized as follows. Chapter 1 demonstrates Synthesis of one dimensional and two dimensional single crystalline nanostructures for applications of biosensor and electronic materials. Chapter 2 reports ultrasensitive CRP (C-reactive protein) detection method employing Au nanoplate and protein G. Chapter 3 describes ultra-sensitive and specific miRNA detection method by using optimized 24-meric PAZ and Au nanowire based SERS sensor. Lastly, chapter 4, demonstrates Single-crystalline β-$Ag_2Se$ nanostructures as a new class of 3D topological insulators.
In chapter 1, we demonstrate Synthesis of single crystalline Au nanostructures and β-$Ag_2Se$ nanostructures using CVD method. In chapter 2, we report super-sensitive detection for CRP employing an ultraclean and ultraflat Au nanoplate. As the CRP is a nonspecific biomarker of inflammation and infection, it can be used as a predictive or prognostic marker for various cardiovascular diseases. Cysteine tagged protein G (Cys3-protein G) immobilized uniformly on the Au nanoplate enable CRP antibody (anti-CRP) to be ordered in a correct orientation, making their binding capacity be maximized for CRP detection. Immobilization condition for the Cys3-protein G and anti-CRP on the Au nanoplate is optimized visually by AFM analysis. Au nanoparticle - Au nanoplate (NPs-on-Au nanoplate) assembly fabricated from sandwich immunoassay for CRP can reduce zero-signal extremely caused by nonspecific bindings, providing a distinct SERS enhancement still in 10-18 M of CRP concentration. Moreover, the NP-on-Au nanoplate sensor shows an excellent selectivity against non-target proteins with high concentration. In addition, comparing with control experiments employing a Au film fabricated by e-beam assisted deposition and linker molecule, we validate clearly contribution of the Au nanoplate and Cys3-protein G for the attomolar sensitive detection of CRP. This detection method can be usable in various sensors employing IgG typed antibody.
In chapter 3, we constructed a range of charge variants of a structure-specific RNA binding protein PAZ as well as multivalent forms of these PAZ variants by using diverse high-valent avidin proteins (2-mer, 4-mer, and 24-mer). Negative charges on PAZ (therefore repulsive to RNAs) proportionally reduced the binding affinities of PAZ to both target and nonspecific RNAs. Increased valency, however, vastly enhanced the binding stability of PAZ to structured target RNA. Surprisingly, we discovered that nonspecific RNA binding of multivalent PAZ can be reduced even below that of the PAZ monomer by controlling negative charges on both PAZ and multivalent avidin scaffolds. The optimized 24-meric PAZ showed nearly irreversible binding to target RNA with negligible binding to nonspecific RNA, and this ultra-specific 24-meric RNA binder allowed SERS detection of intact microRNAs at an attomolar level.
In chapter 4, Single-crystalline β-$Ag_2Se$ nanostructures, a new class of 3D topological insulators (TIs), were synthesized using the chemical vapor transport method. The topological surface states were verified by measuring electronic transport properties including the weak antilocalization effect, Aharonov-Bohm oscillations, and Shubnikov-de Haas oscillations. First-principles band calculations revealed that the band inversion in β-Ag2Se is caused by strong spin-orbit coupling and Ag-Se bonding hybridization. These investigations provide evidence of nontrivial surface state about β-$Ag_2Se$ TIs that have anisotropic Dirac cones.