Dear Parisa,

Thank you for your question regarding SELEX design. In his 2009 paper titled Design, Synthesis, and Amplification of DNA Pools for In Vitro Selection, Dr. Andrew Ellington suggests using primers of approximately 20 nucleotides due to their melting temperature. To avoid secondary structure formation, he suggests using MIT’s web based program PRIMER3. Please let me know if you have further questions.

Best regards,
Elizabeth