OCT背向散射紋理應用於奈米顆粒尺寸分析

Abstract

米繞式(Mirau-based)全域式光學同調斷層掃描術(Full-field optical coherence tomography; FF-OCT) 具有非侵入性(Non-invasive)、高空間解析度以及掃描快速的優勢，被廣泛應用在生醫領域的成像。有別於以往利用FF-OCT的高解析影像分析待測樣品之結構與形貌，本研究探討以本米繞式FF-OCT系統是否能以量測得背向散射紋理，分析出小於系統空間解析度，直徑約為100 nm的奈米顆粒尺寸資訊。 在進行奈米顆粒量測之前，先以量測金屬標準粗糙度測試片，測試系統之絕對定位精準度(Localization accuracy)。金屬標準粗糙度測試片表面刻有1.6、0.8、0.4、0.2、0.1、0.05 µm的粗糙度，本系統量測最小的兩個粗糙度，0.1 µm以及0.05 µm，得到的量測結果誤差分別為1.4%以及20%。驗證基於光源特性、物鏡放大倍率以及取樣速率，本系統具有50 nm的絕對定位精準度。 本研究進一步量測100奈米顆粒溶液，並分析其背向散射紋理以獲得與顆粒尺寸相關的資訊。透過背向散射光強度分析，整理出兩個與尺寸相關之參數：相鄰奈米顆粒之間距，以及奈米顆粒粒徑分布。本研究製備兩種濃度的奈米顆粒溶液，粒子濃度分別為\ 1.6\times{10}^{12}\ 以及\ 8.1\times{10}^{11}\ particles/mL，並探討二者量測得兩個參數的結果。兩種濃度的平均相鄰奈米顆粒間距量測結果分別為0.59 µm以及0.72 µm，與以均勻分布模型估算之兩種濃度顆粒間距，0.85 µm以及1.07 µm比較，誤差分別為30.1%以及32.7%。由於本實驗取樣深度較靠近樣品載台底部，此誤差說明了奈米顆粒在三維空間中分布不完全均勻，較集中在靠近底部的深度位置。而本研究探討粒徑分布之參數為變異係數(Coefficient of variation; CV)。本研究量測得兩種濃度之CV分別為15.24%與15.34%，此一致性歸因於樣品粒徑分布得均勻性。而樣品規格提供之CV為8.6%，量測值相較於樣品規格來說CV值較大，說明散射光強度對於散射顆粒尺寸十分敏感。

Mirau-based full-field optical coherence tomography (FF-OCT) is widely utilized in biomedical 3D imaging, which is benefit from the characteristics of non-invasive scanning, sub-micron resolution and fast scanning speed. Aside from morphological analysis via 3D images, this research attends to exploring FF-OCT’s ability of 100-nm nanoparticles detection, whose sizes are smaller than system’s resolution, which is 0.9 µm. Standard roughness test plate is measured first owing to system’s absolute localization accuracy examination. The roughness plate consists of 6 grinding samples, which are 1.6, 0.8, 0.4, 0.2, 0.1, and 0.05 µm. This research conducts 0.1- and 0.05-µm roughness measurements and yields results with 1.4% and 20% error respectively. In conclusion, this FF-OCT has 50-nm absolute localization accuracy in consideration of its light source bandwidth, objective magnification and sampling rate. 100-nm nanoparticle in solution is measured afterward. Processed backscattered light intensity is analyzed to determine size-related parameters, which are adjacent particles separation and size distribution. Nanoparticle in solution is diluted with 2 concentrations, which are 1.6\times{10}^{12}\ and 8.1\times{10}^{11}\ particles/mL respectively. One parameter, which is adjacent particles separation, of these 2 concentrations are 0.59 µm and 0.72 µm. They have error of 30.1% and 32.7% respectively compared to values estimated with homogeneous distribution model. It can be explained due to the inhomogeneous distribution of nanoparticles in solution. The closer the sampling region is to the bottom, the more likely the nanoparticles are distributed. The other parameter is size distribution, which can be discussed quantitatively in terms of coefficient of variation. CV values of 2 concentrations are 15.24% and 15.34% respectively. This consistency is attributed to the uniformity of sample’s size. Measured CV values are larger than CV from specification, which is 8.6%. This phenomenon describes that scattered light intensity is highly sensitive to scatters’ sizes.