Numerical Simulation of the Photobleaching Process in Laser-Induced Fluorescence Photobleaching Anemometer

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.

Editorial for the Special Issue on MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing

“…Phenomena at the microscale are sometimes difficult to observe, and novel techniques to characterize flow velocities in microchannels include the photobleaching effect. In an in-depth numerical study, Yu Chen et al [7] use a model based on the convection-diffusion reaction equation to study the photobleaching process with reference to a gaussian laser focus region. The study allowed for the determination of the profiles of effective dye concentration and fluorescence, and to find the relationship between the photobleaching time constant obtained by experiments and the photochemical reaction coefficient.…”