使用偏振解析二倍頻顯微術觀測奈米尺度下之分子訊息

Abstract

本論文匯集了偏極化二倍頻的相關應用，二倍頻是一光與物質交互作用的同調過程，其與分子的排列及結構對稱性具有高的靈敏度。這種經由偏振所產生的非線性光學效應具有方向的特性，提供了量化整齊排列的結構參數的可能性。於是產生了許多研究去探討如何調控入射的偏振狀態去分析樣本的結構，例如:研究具疾病的生物樣本在病理上的改變、確認樣本表面或交界面的分子旋性、及二倍頻在奈米材料中的轉換過程。以上的研究都與二倍頻對結構的專一性有很大的關係。因此，具偏振解析的二倍頻顯微鏡已逐漸形成對於生物及材料研究上有利的鑑別工具。關於偏極化二倍頻的應用，它已被用來經張量分析去診斷惡性的黑色素瘤的標地物，類似的方法也應用在求得心臟與肌肉組織的分子排列與非線性光學參數，除此之外，利用組織內部所發出的二倍頻訊號與偏振的相依性去分辨第一型膠原蛋白與肌肉纖維。這些工作促成我們對於偏極化二倍頻的研究以及有助於我們激發更多應用在偏振解析二倍頻顯微鏡的創新。 在我們的研究當中，我們專注於如何使用偏極化的二倍頻，並提供了四個例子去求得不同樣本從結構蛋白質到奈米材料間的分子資訊。章節2.3說明使用具偏振相依性的二倍頻影像去得到澱粉顆粒在三維空間中的分子指向及非線性光學參數。章節2.4說明在厚的生物組織中所觀察到的旋光效應，此方法受惠於二倍頻影像技術針對旋性分子具有高的訊號對比度以及光學切片的能力。章節2.5提供了氧化鋅奈米棒的尺寸效應的詳細解釋，此概念建構在勞倫茲場的效應。此外，Maker條紋技術證實了實驗數據與理論是吻合的。章節2.6致力於架設一具同調性的二倍頻奈米顯微鏡，經由偶氮染料的光致同素異構化反應使分子反轉，此過程具有重複性與飽和特性可作為光學切換去調控二倍頻訊號，連帶著液晶的排列方式也可以藉由此方法而顯現出來。 關鍵字:二倍頻、旋性、勞倫茲局部電場、液晶、光學奈米顯微術

This thesis gathers related studies of the application on polarized SHG. Second harmonic generation (SHG) is a coherent process through light-matter interaction, which is highly sensitive to molecular orientation and structural symmetry. The vectorial nature of polarization-induced nonlinear optical effects provides the access for quantifying the structural factors in ordered structures. Thus it leads to a great number of studies about polarization manipulation on imposed optical field such as pathological change in diseased biomaterial, identification on molecular chirality of surface/interface, and SHG conversion in nanomaterial that are all involving the structural specificity in SHG. Therefore, polarization-resolved SHG microscopy (PSHM) has been evolved into a powerful characterization tool for biological research and material study. About the usage of polarized SHG, it has been exploited to serve as a diagnostic marker in malignant melanoma by χ(2) analysis [1]. Similar method is also allowed for deducing molecular orientation and optical nonlinearities of cardiac and skeletal muscle tissues [2, 3]. Moreover, quantitative discrimination between endogenous SHG sources by their polarization dependences on SHG are utilized to separate type-I collagen fibrils and muscle fibers [4-6]. The earlier works promote our studies for polarized SHG, and assist us to inspire more innovative ideas from PSHM. Among our studies, we emphasize the application of polarized SHG and provide four examples to retrieve molecular information of different samples, ranging from structural proteins to nanomaterials. Section 2.3 describes the practical use of SHG polarization-dependence images to unravel three-dimensional (3D) molecular orientation and intrinsic optical nonlinearities in starch granules. Section 2.4 illustrates the observation of chiroptical effect in thick biotissues, which benefits from the contrast agent for SHG imaging to helical-typed molecules and its optical sectioning capability. Section 2.5 gives in-depth explanations to the size effect on ZnO nanorods (NRs) based on the concept of Lorentz local field. In addition, Maker fringe technique is introduced in verifying the experimental results with our theory. Section 2.6 is dedicated to the construction of a coherent SHG nanoscope. The reversible and saturable optical switch of molecular reorientation via photoisomerization of azo-dye is exploited to control SHG signal, and in turn reveals detailed orientation order of liquid crystal. Key word: second harmonic generation, chirality, Lorentz local field, liquid crystal, optical nanoscopy