Sarshar Mohammad, Wong Winson T, Anvari Bahman
J Biomed Opt. 2014;19(11):115001. doi: 10.1117/1.JBO.19.11.115001.
Optical tweezers have become an important instrument in force measurements associated with various physical, biological, and biophysical phenomena. Quantitative use of optical tweezers relies on accurate calibration of the stiffness of the optical trap. Using the same optical tweezers platform operating at 1064 nm and beads with two different diameters, we present a comparative study of viscous drag force, equipartition theorem, Boltzmann statistics, and power spectral density (PSD) as methods in calibrating the stiffness of a single beam gradient force optical trap at trapping laser powers in the range of 0.05 to 1.38 W at the focal plane. The equipartition theorem and Boltzmann statistic methods demonstrate a linear stiffness with trapping laser powers up to 355 mW, when used in conjunction with video position sensing means. The PSD of a trapped particle's Brownian motion or measurements of the particle displacement against known viscous drag forces can be reliably used for stiffness calibration of an optical trap over a greater range of trapping laser powers. Viscous drag stiffness calibration method produces results relevant to applications where trapped particle undergoes large displacements, and at a given position sensing resolution, can be used for stiffness calibration at higher trapping laser powers than the PSD method.
光镊已成为与各种物理、生物和生物物理现象相关的力测量中的一种重要仪器。光镊的定量使用依赖于对光阱刚度的精确校准。我们使用在1064 nm波长下运行的同一光镊平台和两种不同直径的珠子，对粘性阻力、能量均分定理、玻尔兹曼统计以及功率谱密度（PSD）作为校准焦平面上捕获激光功率在0.05至1.38 W范围内的单光束梯度力光阱刚度的方法进行了比较研究。当与视频位置传感手段结合使用时，能量均分定理和玻尔兹曼统计方法在捕获激光功率高达355 mW时表现出线性刚度。被捕获粒子布朗运动的PSD或针对已知粘性阻力的粒子位移测量可在更大范围的捕获激光功率下可靠地用于光阱的刚度校准。粘性阻力刚度校准方法产生的结果适用于被捕获粒子发生大位移的应用，并且在给定的位置传感分辨率下，可用于比PSD方法更高捕获激光功率下的刚度校准。
