Abstract
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.
Highlights
Laser-induced fluorescence photobleaching anemometer (LIFPA) is a velocity measurement technique developed by Wang in 2005 [1] and primarily for micro/nanofluidics
We studied the photobleaching process of fluorescent dye in the laser focus region, according to the model based on the convection–diffusion reaction equation
The relationship between the commonly used photobleaching time constant obtained by experiments and the photochemical reaction coefficient was revealed
Summary
Laser-induced fluorescence photobleaching anemometer (LIFPA) is a velocity measurement technique developed by Wang in 2005 [1] and primarily for micro/nanofluidics. It measures flow velocity due to the photobleaching nature of fluorescent dye under a high laser power density. The relationships among the complex fluorescent dynamics, the photobleaching reaction process and the superficial and measurable experimental parameters (e.g., τ) have not been established. This could be a major obstacle to the development of the LIFPA technique. In this investigation, the photobleaching process is studied as a photochemical reaction, which can be further numerically analyzed by a convection–diffusion reaction process. The spatial resolution of LIFPA was revisited to better understand the photobleaching phenomenon in flowing liquids and to develop new flow diagnostic techniques
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call