Evanescent Wave Optical-Fiber Aptasensor for Rapid Detection of Zearalenone in Corn with Unprecedented Sensitivity

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

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.

Recent Progress in Functional-Nucleic-Acid-Based Fluorescent Fiber-Optic Evanescent Wave Biosensors

Biosensors capable of onsite and continuous detection of environmental and food pollutants and biomarkers are highly desired, but only a few sensing platforms meet the "2-SAR" requirements (sensitivity, specificity, affordability, automation, rapidity, and reusability). A fiber optic evanescent wave (FOEW) sensor is an attractive type of portable device that has the advantages of high sensitivity, low cost, good reusability, and long-term stability. By utilizing functional nucleic acids (FNAs) such as aptamers, DNAzymes, and rational designed nucleic acid probes as specific recognition ligands, the FOEW sensor has been demonstrated to be a general sensing platform for the onsite and continuous detection of various targets ranging from small molecules and heavy metal ions to proteins, nucleic acids, and pathogens. In this review, we cover the progress of the fluorescent FNA-based FOEW biosensor since its first report in 1995. We focus on the chemical modification of the optical fiber and the sensing mechanisms for the five above-mentioned types of targets. The challenges and prospects on the isolation of high-quality aptamers, reagent-free detection, long-term stability under application conditions, and high throughput are also included in this review to highlight the future trends for the development of FOEW biosensors capable of onsite and continuous detection.