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.