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Study on Fabrication of Controlled Self-assembly of Gold Nanoparticles and Their Corresponding Optical Properities

Author: WangYan
Tutor: ZhangQiQing
School: Beijing Union Medical College
Course: Biomedical Engineering
Keywords: gold nanorods gold nanoparticles controlled assembly
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 148
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Abstract

In recent years, with the rapid development of nanotechnology, metal nanoparticles have been extensively investigated due to their unique optical, electrical and catalytic properties compared with those of the bulk. Exciting properties emerge when these individual nanoparticles form a 1-D, a 2-D or a 3-D assembly. The ability to control the assembly structure leads to tunable optoelectronic properties of the aggregate and attracts great interest and remains a great challenge. In this thesis, investigations on how to fabricate different assembly of anisotropic gold nanorod (GNRs) as well as fabricating assemblies containing different shaped particles-gold nanosphere and gold nanorods while control which faces GNPs are assembled onto GNRs have been made. Besides, study on the optical properties resulting from different assemble structures has also been conducted. The main contents are as follows:1. Assemble anisotropic gold nanorods (GNRs) into different superstructure. GNRs were synthesized through seed mediated growth procedure, the side faces of which are heavily capped by CTAB bilayer while the end faces remain relatively bare, thus makes the ends much easier to be modified. So the hetero functional PEG (SH-PEG-COOH, Mw-459) preferentially attached onto the ends of GNRs through Au-S bond while providing carboxylic acid group for further modifications. Then, a biotin molecule which has an amine group at one end (Biotin-PEO-Amine) was anchored to this carboxylic acid group via the well-known carbodiimide chemistry. This process biotinylated only the end faces of GNRs. Addition of streptavidin further led to end to end assembly of GNRs through the specific recognition and binding ability between streptavidin and biotin. TEM images clearly showed GNRs assemble into chain-like patterns and UV-Vis spectra recorded the red shift of longitudinal SPR when end to end assembly motif formed.2. To assemble GNRs into side-by-side structure, this study devised to introduce thiol-PEG (SH-PEG-CH3O, Mw-2000) in low concentration with sufficient amount; they not only preferentially attached onto the end faces of GNRs but also fully occupied the whole end faces. In consequence, the afterwards addition of SH-PEG-COOH preferentially conjugated to the side faces of GNRs and formed partial coverage on these faces while presenting active groups (COOH) to be tethered with biotin through carbodiimide chemistry. Addition of streptavidin further led to side by side assembly of GNRs through the specific recognition and binding ability between streptavidin and biotin. TEM images showed that GNRs assemble into ladder patterns and UV-Vis spectra recorded the blue shift of longitudinal SPR when side by side assembly motif formed, along with decreasing intensity.3. To achieve the end-to-side assembly motif of GNRs, two batches of GNRs were modified separately. One type of GNRs carried biotin preferentially on the end faces while the other type conjugated streptavidin almost exclusively on the side faces. TEM images showed that side-modified streptavidin-GNRs and end-modified biotin-GNRs building blocks assembled in’T’,’Ⅱ’,’Π’ or ’Ⅲ’ patterns. UV-Vis spectra showed that longitudinal SPR band red shifted to longer wavelength when end to side assembly motif formed.4. The study made a rational design to fabricate GNPs-GNRs assembly motifs. GNPs attached either on the end or the side faces of GNRs by the specific recognition of biotin and streptavidin (SA). For the side by side (SS) assembly motif, streptavidin was introduced onto the side faces of GNRs by electrical interaction while biotin covalently conjugated onto GNPs. With the bio-recognition of biotin and streptavidin, GNPs can assemble on the sides of GNRs. Moreover, for the end to end (EE) assembly, biotin was preferentially conjugated to the end functionalized GNRs via covalent coupling while GNPs were modified with streptavidin. After mixing GNPs with GNRs, end to end assembly structures were obtained. UV-Vis spectra and Zeta-potential value were utilized respectively to characterize surface modifications of GNPs or GNRs. Finally, TEM images and UV-Vis spectra demonstrated that GNPs were assembled onto different faces of GNRs with control. This method could be further used to fabricate controllable assembly of other shaped nanomaterials.

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