Protein crystal harvesting using the RodBot: a wireless mobile microrobot

A new micro-agent is proposed to assist in automated protein crystal harvesting. The microrobot, named the RodBot, is a wireless mobile device driven by rotating magnetic fields (field strength 5-10 mT). When the RodBot rolls on a substrate in a low Reynolds number liquid environment, it generates flows to lift up and trap crystals in a vortex above itself. The gentle fluidic force acting on the crystals is in the range of a few nanonewtons to tens of nanonewtons and is spread over the whole surface of the crystal. The RodBot is capable of trapping protein crystals ranging from a few micrometres to sub-millimetre size. The trapped crystal can be transported to and deposited onto a loop positioned to accept it, obviating the need for more complicated `fishing' systems dependent on particular motions of the loop, the presence of further manipulators or the use of mechanical grippers. The RodBot can be driven in 24- and 96-well plates or in a crystal soaking dish, making the system compatible with existing crystallization hardware.