| Summary: | 碩士 === 國立中正大學 === 化學所 === 97 === Gold nanospheres exhibited localized Plasmon resonance (LPR), a phenomenon caused by the collective oscillation of surface electrons induced by electromagnetic wave. The frequency and intensity of the LPR band are sensitive to the refractive index of the surrounding medium of the nanosphere. In this study, we tried to utilize a shorter sensing depth, where the sensing depth is defined as the distance from the nanosphere surface within which a change in refractive index causes a change in the optical properties of the immobilized nanosphere, to explore the feasibility of using small gold nanosphere for the detection of small molecules. The major aim of this study is to improve the sensitivity of LPR sensor for detection of low molecular weight analytes.
First, gold nanospheres of ~5nm and ~22nm were synthesized and immobilized on glass substrates. The nanospheres were then modified with mercaptoundecanic acid (MUA) to detect the adsorption of positively charged amine compounds: dodecylamine and 4,7,10-trioxa-1,13-tridecanediamine, on the surface of MUA-modified gold nanosphere. Results show that the relative change of absorbance is significantly larger for gold nanosphere of ~5nm than that of gold nanospheres of ~22nm.To examine the biosensing sensitivity, streptavidin-biotin pair was chosen as the model pair in this study. The nanospheres were then modified with streptavidin. Result indicate that gold nanosphere of ~5nm is more sensitive than that of ~22nm for detection of biotin at 10-5M.
One of the LPR sensors used is a novel fiber-optic LPR sensor. The biotin-streptavidin pair was used as the model compounds in this study. Two different approaches were used to evaluate the effect of nanoparticle size on biosensing : (a) nanospheres-immobilized optical fiber was modified with streptavidin to detect biotin (b) nanospheres-immobilized optical fiber were modified with biotin to detect streptavidin. In part (a), the result show that sensitivity of gold nanospheres of 10~15nm is the best among the four sizes of nanospheres, 4~6nm,10~15nm,24~27nm,and 35~45nm, for detection of small molecules. In part (b), and results show that the size of nanospheres does not significantly affect the sensitivity for detection of high molecular weight analytes.
This research demonstrates that smaller size gold nanospheres can improve the sensitivity toward detection of small molecules by LPR sensors.
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