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The goal of this work is to make progress in the domain of near-wallvelocimetry. The technique we use is based on the tracking of nanoparticles inan evanescent field, close to a wall, a technique called TIRF (Total InternalReflection Fluorescence)-based velocimetry. At variance with the methodsdeveloped in the literature, we permanently keep track of the light emitted byeach particle during the time the measurements of their positions ('altitudes')and speeds are performed. By performing the Langevin simulation, we quantifiedeffect of biases such as Brownian motion, heterogeneities induced by the walls,statistical biases, photo bleaching, polydispersivity and limited depth offield. Using this method, we obtained slip length on hydrophilic surfaces of 1$\pm $5 nm for sucrose solution, and 9$ \pm $10 nm for water; On hydrophobicsurface, 32$ \pm $5 nm for sucrose solution, and 55$ \pm $9 nm for water. Theerrors (based on 95% confidence intervals) are significantly smaller than thestate-of-the-art, but more importantly, the method demonstrates for the firsttime a capacity to measure slippage with a satisfactory accuracy, whileproviding a local information on the flow structure with a nanometricresolution. Our study confirms the discrepancy already pointed out in theliterature between numerical and experimental slip length estimates. With theprogress conveyed by the present work, TIRF based technique with continuoustracking can be considered as a quantitative method for investigating flowproperties close to walls, providing both global and local information on theflow.

Near-wall nanovelocimetry based on Total Internal Reflection Fluorescence with continuous tracking