Systematic evolution of ligands by exponential enrichment (SELEX) is a combinatorial chemistry technique in molecular biology for producing oligonucleotides of either single-stranded DNA or RNA that s...Systematic evolution of ligands by exponential enrichment (SELEX) is a combinatorial chemistry technique in molecular biology for producing oligonucleotides of either single-stranded DNA or RNA that specifically bind to a target ligand or ligands.