The power of DEL technology derives from its ability to screen massive libraries, and there have been notable successes . However, the technology also has limitations: the chemical diversity of the library is restricted by the need to carry out the synthesis in aqueous solutions and under conditions in which DNA is stable, the DNA barcode can interfere with binding and add noise to the data, compounds in the library often have physicochemical properties that do not make them ideal chemical starting points for optimization, and the time and cost of synthesizing hundreds of compounds od DNA can be substantial .