3-Dimensional Gold Nano-network using Electrochemical Deposition for Biosensor Applications

Abstract

pH4.0, 90 to 300 sec @ -1.0 to -1.2 V, according to given CNT networking and pillar height. Tailoring of gold thickness and morphology were practicable through a combination of various biasing conditions including bias voltage, time, and duty cycle. The crystallographic properties of gold by ECD were superior enough to exhibit the preferred orientation of (111) plane without annealing. Moreover, the grain sizes of gold were much smaller than those of gold by physical vapor deposition method, resulting in coaxial deposition and smooth surface of nano-networks. 3D gold nano-networks were optically characterized by localized surface plasmon resonance (LSPR) technique, and then it revealed that 3D gold nano-networks showed an excellent reflectance interferometric behavior which is dominantly dependent on the height of pillar structure. This observation was well matched to the calculated regulations of peak positions and intervals by Bragg’s equations. The capability of reflective interferometry with LSPR to biosensor was verified by applying 3D gold nano-networks to sensing biomolecules chemically bound on deposited gold nanoparticles. Absorbance peaks of an optical biosensor using 3D gold nano-networks were remarkably red-shifted according to the sequence of conformational changes. Electrochemical characteristics of 3D gold nano-networks were evaluated by cyclic voltammetry technique in a ferro/ferricyanide system with buffer solution. The results represented good voltammograms surpassing that of 3D networks of CNTs substrates obviously. The difference of peak potentials (Epa-Epc) of 3D gold nano-networks was smaller than that of 3D networks of CNTS, implying faster electron transfer process, but got larger slightly with bigger heights of pillar structures. And also the peak currents of 3D gold nano-networks were enhanced by the additional surface area of both pillar structure and suspending gold nano-strands, which were out-of-electrode-plane. To explain the measured peak currents of 3D gold nano-networks working electrodes, Randle-Sevcik equation is extended to 3D configuration form by introducing the morphological factor (α), which can be extracted from the normalized peak current plots. The feasibility of an electrochemical biosensor using 3D gold nano-networks was testified by sensing the hydrolysis of paraoxon with different concentrations. Chronoamperometric curves displayed a good sensitivity down to 1ppb of paraoxon concentration. A variety of data analyzed using 3D gold nano-networks strongly indicated the synthetic advantages in biosensing applications, that originate from the dimensionally lofty structures combined with the inherent talents of gold. It is highly expected that 3D gold nano-network will be utilized for the applications beyond biosensor, where need these noble advantages.; The fabrication of three-dimensionally (3D) structured gold electrodes must be a worthy endeavor to provide the increased surface area and the hierarchical structure, which are for improving the intensity of signal and the response time of biochips, depending on both the dimensions of biomaterials and the spatial structure of gold electrode. This thesis describes three-dimensional (3D) gold nano-networks based on 3D networks of carbon nanotubes (CNTs) using electrochemical deposition (ECD) and its biosensing applications. 3D networks of CNTs were directly synthesized on Si micro-pillar structured substrates by means of low pressure thermal chemical vapor deposition and the height of pillar was controlled to 1, 3, 5 and 8 μm. For suspending CNTs between pillars in ECD solution, Pt layer by physical vapor deposition technique was introduced to materialize a barrier to the acidity as well as the shell to massive liquid processes. CNT networking played an important role in ECD to provide electrical paths through Pt flakes which are discontinuously deposited on sidewall of pillars. Considering 3D structure of substrates, 3D diffusion-controlled process in ECD was carefully investigated and then evidenced by the incomplete gold deposition on 13 μm heights pillar structures. However, this concern was not realized with shorter pillar structures such as 3 μm or less. In line with an issue of the difficulty in 3D mass transfer during ECD process, pulsed DC plating was adopted to assist mass transfer from the outer of 3D structure as well as to control the morphology of deposited gold. 3D gold nano-networks were optimized with conditions