Abstract
The manipulation of fluids in micro/nanofabricated systems opens new avenues to engineer the transport of matter at the molecular level. Yet the number of methods for the in situ characterization of fluid flows in shallow channels is limited. Here we establish a simple method called nanoparticle velocimetry distribution analysis (NVDA) that relies on wide field microscopy to measure the flow rate and channel height based on the fitting of particle velocity distributions along and across the flow direction. NVDA is validated by simulations, showing errors in velocity and height determination of less than 1% and 8% respectively, as well as with experiments, in which we monitor the behavior of 200 nm nanoparticles conveyed in channels of ~1.8 μm in height. We then show the relevance of this assay for the characterization of flows in bulging channels, and prove its suitability to characterize the concentration of particles across the channel height in the context of visco-elastic focusing. Our method for rapid and quantitative flow characterization has therefore a broad spectrum of applications in micro/nanofluidics, and a strong potential for the optimization of Lab-on-Chips modules in which engineering of confined transport is necessary.
Highlights
Position results from the convolution of advection with diffusion along and across streamlines in the x- and zdirections, respectively
Note that hydrodynamic interactions (HI) with the walls are disregarded in the text in order to obtain tractable expressions, but they are considered for fluid flow characterizations using the numerical expressions derived from the work of Pasol et al.[19,20,21,22] (Supplementary Fig. S1)
Because transverse migration is disallowed at vanishing Reynolds number in Newtonian fluids[23], particles are assumed to be homogeneously distributed across the channel height, allowing us to compute the velocity distribution without fluctuations after derivation and reversion of Eq (1)
Summary
Hubert Ranchon[1, 2], Vincent Picot1, 2 & Aurélien Bancaud[1, 2] received: 22 October 2014 accepted: 31 March 2015 Published: 14 May 2015. Because transverse migration is disallowed at vanishing Reynolds number in Newtonian fluids[23], particles are assumed to be homogeneously distributed across the channel height, allowing us to compute the velocity distribution without fluctuations after derivation and reversion of Eq (1) (middle panel of Fig. 1C) Note that this assumption imposes the use of high ionic strength buffers in order to screen out wall/tracer electrostatic interaction. We checked whether NVDA was relevant to measure the flow velocity and channel height For this we ran running Brownian dynamics simulations of 100 or 200 nm particles conveyed in shallow channels of different heights (see methods section for details on the modeling of advection and diffusion with HI). We computed the repartition of particles derived from the velocimetry distribution (datasets in Fig. 5B), and
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