雷射鑷夾應用尺度的拓展:奈米級解析粒子追蹤與釐米級力場線形捕捉

Abstract

以雷射鑷夾為基礎的應用技術，已經成為研究生物的重要工具。目前，主要的發展可以分為兩個部份:一為利用雷射鑷夾如彈簧一般的線性恢復力的特性，並結合一單一粒子的光學追蹤系統，量測作用於微粒子的待測力。另一為提升光對微粒子的作用範圍，以操控微粒子或細胞至特定的位置或排列特定的圖案。 對於單一粒子的光學追蹤系統中，經常使用四象限光偵測器(QPD)量測由捕捉雷射因接觸微粒子所散射的前向或背向散射光斑。然而，此方法僅適用於半徑小於波長的微粒子。因此，在系統中我們加入一道探測雷射光，並且透過實驗與理論，以及根據不同尺寸的微粒子，尋找出最佳化探測光束焦點的位置：對於前向與背向散射的架構來說，最佳化的探測光束焦點的位置分別為捕捉中心的前方3.3倍與後方2倍微粒子半徑的位置。這一探測光束離焦的架構能夠明顯地提升QPD訊號的靈敏度，此訊號靈敏度最大可以解析奈米等級以上的微粒子偏移量，同時這最佳化的光學架構也增加QPD訊號對微粒子偏移量的可偵測範圍。 另外，為了擴大光對微粒子群的作用範圍，我們也設計了一高數值孔徑的柱形面鏡晶片，產生了一帶有球形像差的線形捕捉光。作用的長度約為0.9 mm，並且縱向球形像差的大小約為30 □m。一高度為40 □m的微流道被製做在這晶片上。因此，在這微流道中，焦點群可吸引在不同高度直徑為10 □m的微粒子，並且在流道的頂端形成一串珠。當啟動微量注射幫浦驅動水流時，微粒子以34度的入射角進入線形捕捉區速度，只要微粒子速度低於58 □m/sec，微粒子將會被線形捕捉光所導引前進。最後，此晶片的製作成本便宜，並且具有用完即拋的特性。

The techniques based on optical tweezers have become an important tool for the biologic research. At presently, there are two main developments of the optical tweezers technique. At first, the feature of the optical tweezers applies a linear restore force on the trapped particle. Thus, this feature combing a trapped particle tracking system is utilized to detect the target force. The other development is to enhance the attractive range of the optical force for manipulating cells to the specific positions or to form the specific maps. For a single particle system, a quadrant-photo diode (QPD) is usually utilized to track the trapped particle by measuring the forward or backward scattering light pattern of the trapping laser from the particle. This method is appropriate for the particle radius small than the trapping laser wavelength, only. Thus, we add an extra probe in the system to track a larger particle. With different sized particles, we investigate the optimized focal offsets between the probe and the trapping lasers experimentally and theoretically. The optimized focal offsets are a 3.3-fold radius ahead and 2.0-fold radius behind the trapping laser focus in the forward and the backward tracking configurations, respectively. These two configurations not only enhance the QPD signal sensitivity but also enlarge the tracking range of the particle position obviously. To expand the attractive range of the optical force, we also design a cylindrical mirror chip with a PDMS immersion layer to form a millimeter-sized optical line segment and a 30 □m longitude spherical aberration. 10 μm-in-diameter particles are attracted by this light pattern at different layers in a 40-□m-height fluidic channel and arranged a line on the top surface of the fluidic channel. Additionally, The particles move along the optical line segment stably with the velocity less than 58 □m/sec and the incident angle is 34。. This cost-effective and large-scale optical line guiding can be achieved in our design.