Control Aggregation Of Gold Nanoparticles For Colorimetric Assay Of Biotin And Streptavidin

Gold nanoparticles(AuNPs) has unique physical and optical properties such as surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS),nonlinear optical (NLO) properties. Gold nanoparticles-based biosensors have found wide application in electrochemical, SERS, fluorescent and colorimetric assays.Gold nanoperticles have absorbance properties due to Surface Plasmon Resonance (SPR). Surface Plasmon Resonance is generated by the collective oscillation of the conduction electrons at the nanoparticle surface induced by an interacting electromagnetic field.SPR band can be influenced by size, shape, temperature, solvent and distance between the particles. When AuNPs are close to each other, a significant absorption band shifts in the visible region of the electromagnetic spectrum. The aggregation of AuNPs provides an opportunity for simple colorimetric assays with AuNPs.Strept(avidin)(STV) is a tetrameric protein, it binds with the biotin, with extremely high affinity constant Ka,2.3×1013M-1. Due to the high affinity of streptavidin for biotin, the biotin-streptavidin system can be used for a large number of biological applications, such as immuoassays, nucleic acid hybridization,amplification assay, and DNA sequencing.In this thesis two biosensors was developed for biotin and streptavidin detection respectively as the following;1-A simple and sensitive colorimetric sensor for biotin detection was designed based on the streptavidin induced aggregation of gold nanoparticles.Streptavidin-functionalized gold nanoparticles was used as a probe (STV-AuNPs). In the present of biotin,the color was changed from red to blue, due to the streptavidin induced the aggregation of STV-AuNPs. The aggregation was investigated with using UV-Vis spectrometer.2-We have developed a new and sensitive detection method of streptavidin. Streptavidin has affinity for2-[(4-hydroxyphenyl)azo]benzoic acid (HABA) organic dye.Due to this high affinity, the probe was developed for streptavidin detection. Thiol-DNA-HABA(TDH) functionalized gold nanoparticles served as sensoring probe. Thiol-DNA was used as a linker for HABA to adsorb on gold nanoparticles surface through thiol groups. In the present of streptavidin, upon sodium choride salt addition there was aggregation of Thiol-DNA-HABA/AuNPs. The aggregation was investigated with using UV-Vis spectrometer and transmission electron microscopy (TEM).