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Anterior gradient-2 (AGR2) is a protein whose function is proving to play an increasingly critical role in a diverse range of biological systems, including vertebrate tissue development, inflammatory tissue injury responses, and cancer progression[1].AGR2 has been found overexpressed in many cancer tissues especially in gland cancers.The aim of this research is to identify aptamers that can bind selectively to AGR2 for the development of assay development of cancer diagnosis.Using a recombinant AGR2-GST protein as target and GST as counter target, we have identified a group of DNA aptamers that can specifically bind to AGR.2 with a Kd in the nanomolar range after 14 rounds of selection.Amoung a group of aptamers, C14B was chosen to further investigation due to its G-rich sequence and high binding affinity.The G-rich region of this binding motif was further characterized to fold into intramolecular parallel G-quadruplex by CD spectrum and UV.Our results indicated that the stability of the G-quadruplex structure is strongly dependent on the nature of the monovalent ion.The effect of ions on the stability of the G-quadruplex is K+>Na+>Li+.The strong dependence of the binding affinity of C14B on K+ concentration suggested that the formation of G-quadruplex structure is important for the binding of aptamer to its target.Furthermore, we have designed a kind of allosteric molecule beacon (aMB) based on C14B, which allowed the detection of nM AGR2 in complex biological samples such as cell medium, suggesting its potential application in cancer diagnosis.