Measurement of velocity fluctuations in microfluidics with simultaneously ultrahigh spatial and temporal resolution

Abstract

Although unsteady and electrokinetic flows are widely used in microfluidics, there is unfortunately no velocimeter today that can measure the random velocity fluctuation at high temporal and spatial resolution simultaneously in microfluidics. Here we, for the first time, theoretically study the temporal resolution of laser induced fluorescence photobleaching anemometer (LIFPA) and experimentally verify that LIFPA can have simultaneously ultrahigh temporal \(({\sim } 4\,\upmu \hbox {s})\) and spatial \(({\sim }203\,\hbox {nm})\) resolution and can measure velocity fluctuation up to at least 2 kHz, whose corresponding wave number is about \(6\times 10^6\,{/}\hbox {m}\) in an electrokinetically forced unsteady flow in microfluidics.