| Noble metal nanoparticles (NPs), especially gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs), have drawn significant attention due to their unique and tunable optical properties caused by surface plasmon resonance (SPR). Bimetallic nanoparticles (NPs) have attracted growing interest. Compared to single-element nanoparticles, core-shell bimetallic NPs consisting of two different metallic elements exhibit improved physical and chemical properties (such as unique optical, electronic, and catalytic properties) due to versatile tunable plasmonic properties as well as extremely amplification of plasmon resonances induced by synergistic interplay between different metallic components. Au/Ag core-shell nanoparticles (Au/Ag core-shell NPs) exhibit widely tunable broadband enhancement of plasmonic resonance, greatly surpassing single-element nanoparticle, which making them good candidates for ultrasensitive detection and biosensing applications. This thesis focuses on the fabrication of colorimetric biosensors for sensitive detection of hydrogen peroxide (H2O2), glucose and cholesterol by using Au/Ag core-shell NPs as optical probe. The details are summarized as follows:(1) Au/Ag core-shell NPs were prepared by using the seed growth method and the colorimetric sensors to detect H2O2 and glucose were designed based on Au/Ag core-shell NPs. First of all, Au/Ag core-shell NPs were synthesized in aqueous solution through the consecutive two-step chemical reduction reactions using the seed growth method. Then, by using Au/Ag core-shell NPs as an optical sensor, a colorimetric method for the ultrasensitive detection of H2O2 and glucose was develpoed. GOx can specifically catalyze the oxidation of glucose in the presence of oxygen to produce H2O2. AgNPs (AgO) from Au/Ag core-shell NPs was oxidized to Ag+by H2O2. The conversion of AgNPs to Ag+leads to a significant decrease of the SPR absoption peak of Au/Ag core-shell NPs accompanied by the color change, which forms the basis for sensitive colorimetric H2O2 and glucose sensing. The detection limit of the biosensors for H2O2 and glucose were 0.11 ?M and 0.24 ?M, respectively. The biosensors exhibited a high sensitivity and favorable selectivity. The quasi-quantification of H2O2 and glucose could be observed by naked eyes. The methods can be applied to detect glucose in complex samples. Therefore, the proposed method has a broad prospect in clinical diagnosis applications.(2) A colorimetric biosensor for cholesterol detection based on Au/Ag core-shell NPs has been developed. Cholesterol oxidase (ChOx) specifically catalyzes the oxidation of cholesterol by oxygen to 4-cholesten-3-one and H2O2. The selective dissolution of Ag from the preformed Au/Ag core-shell NPs by H2O2 caused the decrease of the SPR absorption of the resultant Au/Ag core-shell NPs. Meanwhile, the color of the solution changed during this process. Thus a colorimetric biosensor was developed and it was applied to sensitive detection of cholesterol. The linear range for cholesterol was from 0.3 to 300 ?M. The detection limit for cholesterol was as low as 0.15 ?M. This method displayed some advantages over the currently existing methods such as simple because no additional chromogenic agents and no laborious and time-consuming enzyme conjugation processes were necessary, high sensitivity due to the high molar extinction coefficient of AgNPs, ease of operation, rapid and direct readout with naked-eyes, and applicable in complex samples. |
PDF Full Text Request