Fig. 1: Generation of a localized optofluidic barrier.
From: Three-dimensional optofluidic control using reconfigurable thermal barriers
a, Conceptual representation of particles moving around a physical barrier made of a single pillar (left) and an optofluidic pillar (right) established by light-induced heating that creates local fluid flows (black arrows). b, Three-dimensional temperature profile used to create an optofluidic pillar with a single laser beam (P = 20 mW) on a plasmonic surface. Experimentally measured (left) and computed from simulations (right). c, Maximum temperature increase ΔTmax over the projected laser power P on the sample, experimentally measured (Exp., dots) and simulated (Sim., line) above room temperature (Tamb = 23 °C). Absolute temperatures correspond to T = Tamb + ΔT. d, Using an SLM, the incoming light beam is reflected and split into two, focused on each side of a microfluidic chamber (light grey) with absorbing surfaces (dark grey), leading to two opposing pillars. e–g, Comparison of experimentally measured (left) and simulated (right) fluid flows using silica tracer particles (dp = 1.5 μm) for different planes (blue, green and purple) between two hot spots in a chamber of thickness h = 20 μm. e, Radial symmetric flows towards the centre are observed near the surface (z = 2 μm) due to thermo-osmotic flows. f, Across the chamber, flows are moving along the surfaces, converging from both sides in the middle, from where they form closed-loop flow profiles back to the surface (y = 25 μm). g, Along the vertical axis, additional convective flows push the fluid upwards (x = 25 μm). h, An optofluidic barrier is created by projecting multiple beams with alternating foci within the microfluidic chamber, demonstrating reconfigurability. i, Simulated optofluidic barrier shows how five hot spots on each side concatenate into each other to form a single heat barrier. j,k, Experimental (left) and simulated (right) trajectories of particles (dp = 5 μm, white lines) sedimenting downwards (vg = 12.7 μm s−1) into the barrier (temperature profile at surface shown), where they are deflected and move around (j), and can even be repelled upwards (k). Scale bars, 3 μm (b), 15 μm (e–g and i–k).
