Non-immobilized GO-SELEX screening of aptamers against cyclosporine A and its application in a AuNPs colorimetric aptasensor

Cyclosporine A (CsA) is an immunosuppressive drug that is widely used in clinical practice. Due to its narrow therapeutic window and the significant differences between individuals, the therapeutic drug monitoring (TDM) of CsA is required to ensure patient safety. In this study, we screened a novel aptamer, named CsA7, which could specifically recognize CsA, and developed a AuNPs colorimetric aptasensor for the rapid detection of CsA. In the SELEX process, after eight rounds of screening, four aptamer candidate sequences were obtained and subjected to binding affinity and specificity tests. Finally, the CsA7 aptamer (K_d = 41.21 ng mL^-1) showed the highest affinity for CsA. Based on CsA7, we also developed a AuNPs colorimetric aptasensor, which had a detection limit of 0.1 ng mL^-1 and a quantitative range of 0.1-500 ng mL^-1 and showed good selectivity among CsA and its analogs. According to the results, the CsA7 aptamer provides an alternative recognition molecule to the antibody in biosensor applications and shows great potential for the rapid and convenient detection of CsA.