Optical-fiber sensor for 17β-Estradiol-binding aptamer evaluation and specific detection of 17β-Estradiol in serum at...

Methods for evaluation of immobilized-small molecule-binding aptamers are rare. In this study, taking the evaluation of 17β-Estradiol (E2) aptamers as an example, we first summarized the reported affinity and specificity results of 16 E2 aptamers, highlighting the issues of insufficient and inconsistent results and the lacking of evaluation of immobilized aptamers. We further exemplified the limited application scope of current affinity techniques by testing the two most widely-applied E2 aptamers, Kim76 and Alsa35, using the three label-free fluorescence assays and two nuclease protection assays. Subsequently, we evaluated the affinity of immobilized-E2 aptamers, Alsa35 and E09, using fiber optic evanescent wave aptasensor (FOEW) based on the competitive binding of target and fluorophore-labeled complementary strand with the fiber surface immobilized-aptamer. The results revealed that Alsa35 had the better affinity and specificity than E09. Using Alsa35-based FOEW, the enzyme-free detection of E2 spiked in river water and human serum was respectively realized with the unprecedented limits of detection (LOD, S/N = 3) of 4.75 (undiluted river water) and 206 pM (undiluted serum). FOEW is a valuable addition to analytical approaches for evaluation of immobilized-aptamers and a general platform for ultrasensitive target detection.