text: Recently, SELEX has expanded to include the use of chemically modified nucleotides. These chemically modified oligonucleotides offer many potential advantages for selected aptamers including greater stability and nuclease resistance, enhanced binding for select targets, expanded physical properties - like increased hydrophobicity, and more diverse structural conformations. 
  The genetic alphabet, and thus possible aptamers, is also expanded using unnatural base pairs the use of these unnatural base pairs was applied to SELEX and high affinity DNA aptamers were generated.