針對金屬奈米結構之螢光生命週期影像失真之研究

Abstract

受激分子的自發性放射可以藉由環境來改變。透過金屬奈米結構來改變受激分子的自發性放射已被廣泛應用在近場光學、光電子學和生醫造影上。利用追蹤發光分子電偶極放光體的自發性輻射速率和環境之間的相互作用並透過自發性放射率反映環境形貌是可行的。在本論文中，我們模擬單一發光分子當作探頭進行空間中一維的掃瞄，進而計算出波賽爾因子以建立針對金奈米柱二聚體的螢光分子週期影像。然而，我們發現發光分子螢光週期影像並非總是能反映金屬奈米結構形貌。電偶極場與奈米結構的顯著偶合早成了影像的失真。我們提出造成影像失 真的因素。金奈米柱的銳利度會造成發光分子自發性放射率劇烈的改變，並在影像失真上扮演重要的角色。發光分子的放光頻率也會造成影像上的失真。我們也探討發光分子的極化方向與影像可性度上的關係。最後，我們利用一個波導理論模型，提出一個能辨識出影像失真的方法。

The spontaneous emission of an excited molecule can be tailored by its environment. Modifications of spontaneous emission rate using plasmonic structures are widely investigated for applications ranging from the near-field optics and optoelectronics to biomedical imaging. It is possible to track the spontaneous emission rate of a dipole emitter to see how it interacts with the environment and responds to the morphology of surrounding. In this thesis, we model the fluorescence lifetime imaging of gold nanorod dimers by considering a single dipole emitter as a sensitive probe scanning along one dimension above the metallic nanostructure. The fluorescence lifetime is spatially mapped out as an attempt to reconstruct the image of nanostructures. It is found that the lifetime imaging is not always consistent with the real morphology of nanostructure. Artifacts in lifetime imaging arise due to the strong coupling between the dipolar field and resonance structures. The sharpness of nanorod dimers makes spontaneous emission rate of a dipole emitter vary dramatically and plays an essential part in artifacts. The frequency of a dipole emitter can also influence the lifetime and cause artifacts. Here, we investigate the relation between the orientations of dipole emitters and fidelity of images. At last, we will address strategies to distinguish these artifacts from the real morphology and present a theoretical model based on the waveguide geometry to examine possible origins of artifacts.