表面電漿子於生醫應用之分析-從感測定量到細胞影像

Abstract

In recent years, surface plasmon resonance (SPR)-based sensor has gained much popularity as a real-time and non-labeling technique to study the interaction between ligands and receptors immobilized on a solid support. The growing applications in biomedical research,in the meanwhile, stimulate the study of underlying factors that affect the SPR signal shifts. The reduction of a gross SPR curve shift to simple physical parameters reveals more physical meanings for the studied molecules. In general, the planar SPR sensor can be viewed as isotropic and homogeneous layers separated by mathematically sharp boundaries. The reflectance can be solved within the framework of the macroscopic Maxwell equations if a local approximation of dielectric constant for each layer can be given. However, the dielectric constant for a nano-scale layer (<30nm) can not be unambiguously referred to as a constant and the exact value may vary from samples to samples, depending on the way of preparations. In most cases where SPR is applied, such as immunoassay, the binding analytes form a discontinuous, inhomogeneous layer on the sensor surface, with dielectric constant hard to be defined. Therefore, in this thesis, the dielectric constant of a discontinuous thin film is first studied in a simple system―a monolayer of distributed gold nanoparticles. The dielectric constant of the nanoparticle monolayer is highly related to its density, and a mathematical description—modified MG model(Maxwell-Garnett effective medium model)— is formulated in this thesis, which gives quite close results to the experiment data. At the wavelength 530nm, both the experiment and calculations indicate the light is in resonance with the gold nanoparticle monolayer at Vr~20.8%. The modified MG model also predicts the enhancement of SPR immunosensing by gold nanoparticles as the experimental data has shown in the past. As gold nanoparticle monolayer has drastically different optical property from bulk gold, the attachment of the analytes with gold nanoparticles will induce much larger SPR perturbation. Since gold nanoparticles can be easily functionalized as immunoprobes, the gold nanoparticle-enhanced SPR immunosensing can be an ideal detection tool for analytes of small molecules or with ultra-low concentrations. In addition, through the labeling of gold nanoparticle, the analyte surface concentration can be inferred from the SPR angle shift using the modified MG model; it is an improvement over conventional SPR methods in which only external analyte concentration can be obtained using an established standard curve. Another scope in this thesis goes beyond the most popular use of SPR as immunoassay; the basic photoluminescence property of gold nanoparticle is studied. Some gold nanoparticles, such as gold nanorods, emit strong photoluminescence under two-photon excitation The efficient, non-bleaching and non-blinking photoluminescence makes gold nanorods an ideal probe or contrast agent in imaging. As expected, the two photoluminescence of gold nanorods is most efficient when the excitation light is in resonance with the surface plasmon mode of gold nanorods. The use of the gold nanorod as an imaging probe in cells is demonstrated and possible use as a local dynamic sensor is also discussed. The thesis is wrapped up with some lingering problems and prospective applications of SPR technique to some biological systems, such as membrane phase transition and membrane protein conformational changes.