a: Steering and Trapping of Live Swimming Cells
We have extended our feedback control methods to steer and trap live swimming cells. Our control works by sensing the position of a chosen microbe visually and then applying a small electric field, that is precisely shaped in space and time, to move that microbe from where it is to where it should be (feedback control) faster than it can swim away. Correction of measured errors by feedback allows control even of cells with unknown properties (e.g. microbes taken from the pond next door) and is gentle and safe. We can position swimming microbes to any desired location, steer them along any desired path as they continue to swim, let them go, and reposition them; and we can do this without directing light at them (the strong light of laser tweezers can sometimes harm living cells). Our key advantage is that it is easy to correct large excursions: even if the microbe is many micrometers away from its desired location, we can create a flow to bring it back.