Thermooptical molecule sieve on the microscale

A combination of thermophoresis and fluid flow can be used to trap molecules and particles. We show that heating by scanning motion of an elongated laser spot creates a strong thermal trap. Additionally, it induces a global fluid flow that feeds the trap. Such thermal sieve can accumulate molecules from a large surrounding region within seconds into a 10 mu m spot. Numerical modeling gives a quantitative prediction of the effect. Traps can be dynamically created, relocated, and tuned, which can be used for particle sorting. (C) 2015 AIP Publishing LLC.