Figure 2. Chip-Based Evolution.

RNA enzymes were evolved over the course of 500 logs of selective amplification. The population was monitored in real time based on fluorescence intensity (middle). After each log of growth, a 10-fold dilution was executed by automated microfluidic manipulation. The substrate concentration was reduced periodically to maintain selective pressure on the evolving population (top). Before each reduction in substrate concentration, sample was removed from the circuit, mutagenized, and reintroduced to the circuit. The interval between successive dilutions was recorded as a function of time (bottom).