準焦與散焦雷射鑷夾之設計與應用

Abstract

過去十年，利用光梯度力捕捉微小物體的雷射鑷夾被廣泛的應用在捕捉與搬運微生物體、及微小粒子的操控上。它的捕捉力強度約在10-12牛頓，所能捕捉的微小物體的大小約在幾十nm到幾十μm。雷射鑷夾目前已成為生物科技研究上一個重要且非常有用的工具。 傳統的雷射鑷夾是將雷射光束準確地聚焦在樣品平面上形成一光點，我們稱之為準焦雷射鑷夾。過去，準焦雷射鑷夾主要被運用於單一微粒子的操控及研究上。為提昇捕捉效率，我們首創了散焦雷射鑷夾，可一次捕捉一群微粒子。在本論文中，我們刻意讓雷射光束偏離樣品平面，使得雷射光束在樣品平面上變成一個大光圈，擴大了捕捉範圍。在本實驗中，我們將實際展現準焦雷射鑷夾分別捕捉單一塑膠珠子、綠膿桿菌、精蟲等的實例操作，同時也展示散焦雷射鑷夾捕捉一群塑膠珠子的功能。 我們利用雷射鑷夾的電磁波模型，模擬了準焦與散焦雷射鑷夾的捕捉力與捕捉範圍。此外，我們還設計了一個流速與捕捉範圍關係的實驗，可同時觀察雷射鑷夾捕捉力及捕捉範圍。我們發現散焦雷射鑷夾與準焦雷射鑷夾最大的不同在於，散焦雷射鑷夾捕捉範圍較準焦雷射鑷夾大，但捕捉力較弱。最後，我們提出一個應用散焦雷射鑷夾系統提昇樣品濃度的裝置設計。 另外，在本論文中我們還敘述了完整的雷射鑷夾的設計指南，可供未來欲架設雷射鑷夾的讀者詳細的參考。我們誠摯地希望本論文不僅能做為研究雷射鑷夾的入門，更能激盪出更多對於雷射鑷夾的應用。

In the past decade, optical tweezers, which is capable of capturing micro objects via the gradient force produced by a converging laser beam, have been widely used in the capture, move, and manipulation of microbiological objects and micro particles. Typically, the force generated by an optical tweezers system is of the order of pico-Newton (10-12 N). The sizes of captured tiny objects range from a few tens of nano-meters to a few tens of micrometers. Optical tweezers have just become an important and powerful tool in biotechnology research. Traditionally, an optical tweezers system is operated by precisely focusing a laser beam into a focal point on the sample plane, which we call an in-focus optical tweezers system. It is commonly used to capture and manipulate a single particle at a time. In order to capture more particles in a short period of time, we innovate an off-focus optical tweezers system for the first time, which captures a group of micro particles at a time. In this thesis, we purposely shift the laser focal point slightly away from the sample plane. This leaves a relatively larger laser spot on the sample plane, which increases the capturing range. In this work, we will show the manipulation of a single polystyrene bead, a pseudomonas aeruginosa, and a spermatozoon, separately, by an in-focus optical tweezers system. Also, we will demo the capture of a group of polystyrene beads by an off-focus optical tweezers system. Based on the EM model of optical tweezers, we simulate the capturing range and the capturing force for the in-focus optical tweezers and the off-focus optical tweezers, separately. Besides, we also design an experiment to measure the relationship between the drift velocity of the solution relative to the captured beads and the capturing range by an optical tweezers system. The variation of the drift velocity clearly illustrates the relationship between the capturing range and the capturing force of an optical tweezers system. We conclude that the off-focus optical tweezers system has a longer trapping range but a weaker trapping force than the traditional in-focus optical tweezers system does. At last, we propose a design for sample concentration utilizing the off-focus optical tweezers. In addition, we present a detailed guideline for the design of optical tweezers. This may be helpful for those who are interested in setting up an optical tweezers system. We hope that this thesis is not only a useful reference on optical tweezers, but also a stimulation for further applications.