In a temperature gradient built by infrared laser heating, polyethylene glycol (PEG) of large concentration moves away from the hot region. The resulting concentration gradient of PEG creates entropic potential well and traps another solute of small concentration due to diffusiophoresis. Here we develop this method to work in two dimensional spaces and time. The steering of laser traps colloids, DNA, and living cells in designed two-dimensional patterns. By modulating laser intensity with time, the protein concentration is periodically controlled in tens of mHz. This method could be useful for a directed assembly of biological materials.
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