Abstract
Advection is critical for efficient mass transport. For instance, bare diffusion cannot explain the spatial and temporal scales of some of the cellular processes. The regulation of intracellular functions is strongly influenced by the transport of mass at low Reynolds numbers where viscous drag dominates inertia. Mimicking the efficacy and specificity of the cellular machinery has been a long time pursuit and, due to inherent flexibility, optical manipulation is of particular interest. However, optical forces are relatively small and cannot significantly modify diffusion properties. Here we show that the effectiveness of microparticle transport can be dramatically enhanced by recycling the optical energy through an effective optical advection process. We demonstrate theoretically and experimentally that this new advection mechanism permits an efficient control of collective and directional mass transport in colloidal systems. The cooperative long-range interaction between large numbers of particles can be optically manipulated to create complex flow patterns, enabling efficient and tunable transport in microfluidic lab-on-chip platforms.
Highlights
Advection is critical for efficient mass transport
In this Letter we prove that high Péclet number (Pe) number regimes can be achieved by taking advantage of optically induced advective flows in a colloidal system
The measured velocities in the experiment are an order of magnitude lower, which could be explained by the finite dimensions of the cuvette; it is known that backflow of displaced water outside the region of action of optical forces apparently slows down the induced advection[22]
Summary
The intracellular and intercellular transport occurs within fluids at low Reynolds numbers with viscous forces dominating inertia In this regime, besides diffusion, advection processes control the transport over larger length scales[1,2,3]. In large plant cells, the cytoplasmic streaming driven by the movement of myosin motors along actin filaments is responsible for circulating microscopic particles or organelles[2,3] This efficient mass transference assisted by the fluid flow happens at large Péclet number (Pe) where advection dominates diffusion. Another function of high Pe fluid flow is enhancing the metabolites mobilization through the rotational streaming of vacuolar fluid[4]. We will show that the transport velocities of the same magnitude as in refs 11,12 can be achieved with two orders of magnitude less intensity
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