Single-file escape of colloidal particles from microfluidic channels

This is the final version of the article. Available from the publisher via the DOI in this record.Single-file diffusion is a ubiquitous physical process exploited by living and synthetic systems to exchange molecules with their environment. It is paramount to quantify the escape time needed for single files of particles to exit from constraining synthetic channels and biological pores. This quantity depends on complex cooperative effects, whose predominance can only be established through a strict comparison between theory and experiments. By using colloidal particles, optical manipulation, microfluidics, digital microscopy, and theoretical analysis we uncover the self-similar character of the escape process and provide closed-formula evaluations of the escape time. We find that the escape time scales inversely with the diffusion coefficient of the last particle to leave the channel. Importantly, we find that at the investigated microscale, bias forces as tiny as 10^{-15} N determine the magnitude of the escape time by drastically reducing interparticle collisions. Our findings provide crucial guidelines to optimize the design of micro- and nanodevices for a variety of applications including drug delivery, particle filtering, and transport in geometrical constrictions.S. P. acknowledges the support from the Leverhulme Trust through an Early Career Fellowship (Grant No. ECF-2013-444), the Wellcome Trust through an Institutional Strategic Support Fund (Grant No. SW- 05377), and the Royal Society through a research grant (Grant No. RG140203). M. P. and E. L. kindly acknowledge funding from the European Research Council under the European Community’s Seventh Framework Program (FP7/2007-2013/ERC) Grant Agreement No. 279004