Chen Yu, Meng Shuangshuang, Wang Kaige, Bai Jintao, Zhao Wei
State Key Laboratory of Photon-Technology in Western China Energy, International Collaborative Center on Photoelectric Technology and Nano Functional Materials, Institute of Photonics & Photon Technology, Northwest University, Xi'an 710127, China.
Micromachines (Basel). 2021 Dec 20;12(12):1592. doi: 10.3390/mi12121592.
At present, a novel flow diagnostic technique for micro/nanofluidics velocity measurement-laser-induced fluorescence photobleaching anemometer (LIFPA)-has been developed and successfully applied in broad areas, e.g., electrokinetic turbulence in micromixers and AC electroosmotic flow. Nevertheless, in previous investigations, to qualitatively reveal the dynamics of the photobleaching process of LIFPA, an approximation of uniform laser distribution was applied. This is different from the actual condition where the laser power density distribution is normally Gaussian. In this investigation, we numerically studied the photobleaching process of fluorescent dye in the laser focus region, according to the convection-diffusion reaction equation. The profiles of effective dye concentration and fluorescence were elucidated. The relationship between the commonly used photobleaching time constant obtained by experiments and the photochemical reaction coefficient is revealed. With the established model, we further discuss the effective spatial resolution of LIFPA and study the influence of the detection region of fluorescence on the performance of the LIFPA system. It is found that at sufficiently high excitation laser power density, LIFPA can even achieve a super-resolution that breaks the limit of optical diffraction. We hope the current investigation can reveal the photobleaching process of fluorescent dye under high laser power density illumination, to enhance our understanding of fluorescent dynamics and photochemistry and develop more powerful photobleaching-related flow diagnostic techniques.
目前，一种用于微纳流体速度测量的新型流动诊断技术——激光诱导荧光光漂白风速仪（LIFPA）已被开发出来，并成功应用于广泛领域，例如微混合器中的电动湍流和交流电渗流。然而，在以往的研究中，为了定性地揭示LIFPA光漂白过程的动力学，采用了激光分布均匀的近似方法。这与激光功率密度分布通常为高斯分布的实际情况不同。在本研究中，我们根据对流扩散反应方程，对激光聚焦区域内荧光染料的光漂白过程进行了数值研究。阐明了有效染料浓度和荧光的分布情况。揭示了通过实验获得的常用光漂白时间常数与光化学反应系数之间的关系。利用所建立的模型，我们进一步讨论了LIFPA的有效空间分辨率，并研究了荧光检测区域对LIFPA系统性能的影响。研究发现，在足够高的激发激光功率密度下，LIFPA甚至可以实现突破光学衍射极限的超分辨率。我们希望当前的研究能够揭示高激光功率密度照射下荧光染料的光漂白过程，以增进我们对荧光动力学和光化学的理解，并开发出更强大的与光漂白相关的流动诊断技术。
