In a recent experimental paper we show how a DNA robot can sort molecules into target piles. The robot itself is very simple, just a strand of DNA. This robot runs around randomly on a 2D DNA origami surface, picking up items to sort and dropping them off at the right place. The robot's walking mechanism is designed to be reversible so that it consumes no energy or fuel while walking. The sorting mechanism uses a little bit of fuel, in the form of DNA hybridisation, just enough to make the sorting process irreversible and prevent subsequent unsorting. How eco-friendly.
Read the paper!