The Monolayer-Encapsulated Gold Nanoparticles Were Purified By Chromatography And Used For Sensing Research

This dissertation focuses on the electronic conducting in monolayer-protected Au nanoparticles which purified by column chromatography as well as the sensing applications, mainly including three parts of work:(1) Octanethiol monolayer-protected gold (nano)clusters (MPCs) at the Au/thiolate mole ratio of 4:1 and 8:1 were synthesized by a Brust two-phase method and purified with column chromatograph, respectively, and characterized with scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis(TGA). Chemiresistor sensors were fabricated with MPCs as sensing interfaces and interdigitated electrodes of two designs (thick and thin electrodes) as transducers. The response profiles are dependent on the electrode size, the MPC size, the purity of MPCs, and the relative magnitude of the permittivity of the analytes to the film. Thick electrodes offer a thick strong electric field that covers the sensing film and cause an extra increase in conductance and capacitance due to the film swelling. Negative resistance responses can be therefore observed upon exposure to compounds with high permittivity. Increasing in particle size reduces the film permittivity. Ionic impurities increase the film permittivity and could produce ionic current. The sensor responses are the results of the changes in the film permittivity, the core-core separation, and the film volume, which provides a complicated response pattern.(2) Column liquid-solid chromatography was used to remove residual impurities of isolated n-octanethiol (C8H17SH) monolayer-protected gold nano-clusters (MPCs) which were synthesized by a Brust two-phase method. Three-dimensional (3D) cross-linked MPC films were prepared directly on interdigitated electrodes to form chemiresistor sensors through the exchange reactions of the chromatographically purified MPCs with 1, 6-hexanedithiol (HDT) or 1, 4-benzenedimethanethiol (BDT). Ionic current induced by trace residual ionic impurities in MPCs was qualitatively detected by comparing the resistance responses of the sensors interfaced with the chromatographically purified and unpurified MPC films by employing volatile organic compounds (VOCs) and water vapor as probes, respectively. The existence of...