An ssDNA library immobilized SELEX technique for selection of an aptamer against ractopamine

An improved SELEX technique was developed for selecting aptamers against ractopamine (RAC) by immobilizing ssDNA library on the magnetic beads. After sixteen selection rounds, a highly enriched ssDNA pool was sequenced and nine families were grouped according to their homology and secondary structures analysis. One representative aptamer candidate from each family was picked out for binding affinity identification by graphene oxide (GO) adsorption platform. The aptamer RAC-6 was demonstrated as the optimal aptamer with high specificity and dissociation constant (Kd) value of 54.22 ± 8.02 nM. To prove the potential application of aptamer RAC-6 in the quantitative determination of RAC, a fluorescent bioassay with aptamer RAC-6 was developed. The linear range for RAC was from 0.10 ng/mL to 100 ng/mL and the limit of detection was as low as 0.04 ng/mL. Furthermore, the method was validated for the analysis of RAC spiked real samples, and the recoveries were between 82.57% and 104.65%.