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다기능 질량기반 마이크로진동자

다기능 질량기반 마이크로진동자
Ko, Wooree
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In this thesis, various types of acoustic resonator, particularly, quartz crystal microbalance (QCM), are developed for biological, chemical and environmental sensing applications. Addressing the drawbacks associated with the conventional type of QCM, the QCM variants are newly developed with improved performance and utilized for appropriate applications. In addition, QCM is integrated with other analytical instruments for clear understanding of ambiguous phenomena. This thesis consists of 4 chapters. Chapter 1 introduces the general background about QCMs and photocatalyis which the most part of the thesis is focused on. Chapter 2 through Chapter 4 are research works about the development of various types of QCM-based sensors for diverse applications. Chapter 2 introduces the development of a novel microgravimetric immunosensor using a WO3 nanoparticle-modified immunoassay and a silver enhancement reaction. When the nanoparticles in silver ion solution (i.e. AgNO3) are exposed to visible light, the silver ions are photocatalytically reduced and form a metallic silver coating on the nanoparticles. This silver coating consequently induces changes in the mass and light absorption spectrum. Although photocatalytic reduction reactions can be achieved using ultraviolet (UV) light and TiO2 nanoparticles, the use of UV light in biosensing applications has drawbacks in that UV light can damage proteins. In addition, conventional quartz crystal substrates must be passivated to prevent undesirable silver ion reduction on their gold-coated sensing surfaces. We addressed these problems by adopting a visible light-induced photocatalytic silver enhancement method using WO3 nanoparticles and lateral field excited (LFE) quartz crystals. As a proof-of-concept demonstration of the technique, streptavidin was adsorbed onto an LFE quartz crystal, and its mass was enhanced by biotinylated WO3 nanoparticles followed by a photocatalytic silver enhancement reaction. The mass change due to the enhancement was found to be > 30 times greater than the mass change by the streptavidin alone.In Chapter 3, the integration of QCM with optical instrument is described for accurate evaluation of photocatalytic activity. An electrodeless QCM, where the electrodes are detached from the quartz surfaces and placed in proximity, was used for integration with optical instrument for transparency, and photocatalytic activity of ZnO nanorods was evaluated. The optical method measures concomitantly occurring photodegradation and oxidative decomposition (photo-mineralization) while the gravimetric method measures resonance frequency shift due to photo-mineralization. Therefore, the simultaneous measurement of the system allows accurate evaluation of photo-mineralization and photo-degradation of methylene blue (MB) molecules adsorbed on ZnO nanorods. We found that the photo-degradation of MB molecules dominantly occurs in the initial stage of photodecomposition. Also, both photodegradation and photo-mineralization are in linear relationship once the photo-mineralization takes place.Chapter 4 is to develop monolithic multichannel QCM using nanostructures and electrodeless QCM for various sensing applications. A monolithic multichannel quartz crystal microbalance (MQCM) sensor was developed via the simple addition of localized masses in different weight. ZnO nanorods in different size of patterns were directly synthesized onto an electrodeless quartz crystal plate as the source of different masses and each pattern resulted in an independently functioning resonator. Also, ZnO nanostructure enhanced the sensitivity through the enlarged sensing area. The adoption of electrodeless QCM configuration significantly simplified the method used to generate multiple resonators and addressed the electrical lining problem by requiring only a single pair of remote electrodes for simultaneous measurements at multiple frequencies. The MQCM developed was tested for its utility as an electronic nose and efficiently distinguished ethanol or toluene-adulterated gasoline from unadulterated gasoline.
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