Monolayer-Encapsulated Gold Nanoparticles Used For Electronic Conducting And Sensing Research

This dissertation focus on the electronic conducting in monolayer-protected Au nanoparticles as well as the sensing applications, mainly including three parts of work: 1). 1-Octanethiol and 2-phenylethanethiol monolayer-protected gold nanoparticles were synthesized, and spray coated on the interdigital microelectrode (IME). The resulted chemiresistor sensors were used for volatile organic compounds (VOCs) analysis. The resistance and capacitance responses were measured simultaneously with an ac LCR meter. The response mechanism of the Au nanoparticle-coated chemiresistor sensors and the electronic communicating between the nanoparticles were investigated based on the response profiles of the sensors to VOCs with different groups at different humidity, as well as the response profiles to water vapor at different concentrations. The chemiresistor sensor showed positive resistance response (increases with concentration) and no capacitance response to water vapor at low humidity; and negative resistance response (decreases with concentration) and significant positive capacitance response at high humidity. 2). A 3-D 1,6-hexanedithiol cross-linked gold nanoparticles thin film was prepared and precipitated on the interdigital microelectrodes based on the one-step exchange cross-linking reactions between the synthesized 1-octanethiol-protected Au nanoparticles and the 1,6-hexanedithiols. The sensing characteristics of the 3-D cross-linked nanoparticle film were compared with those of the 2-D uncross-linked nanoparticles, and the effect of the cross-linking on the electronic communicating and the responses were investigated. The effect of the core-shell structure on the sensing characteristics and the humidity-resisting ability was also investigated. The sensor coated with 1-octanethiol-protected gold nanoparticles show the most sensitivity to VOCs, while the sensor coated with 1,6-hexanedithiol cross-liked nanopartilce show the most humidity-resisting ability. 3). The quartz crystal microbalance (QCM) was used together with the chemiresistor sensor to investigate the sorption of the nanopartilces to vapors. Based on the different response mechanism of the QCM and the chemiresistor sensor, we investigated the sorption and response mechanism of the nanoparticles as sensing interface by in situ observing the electrical and mass signals caused from the sorption.