In order to demonstrate the specific interaction between AGR2 and C14B1, three control proteins BSA, thrombin and trypsin were coupled with the NHS-sepharose-beads and then were incubated with C14B1. As shown in Figure 3 , C14B1 could bind to target AGR2 strongly, while there were no or little binding affinity towards thrombin, BSA and trypsin, demonstrating the high selectivity of the aptamer.