Mismatched duplexed aptamer-isothermal amplification-based nucleic acid-nanoflower for fluorescent detection of okadaic acid.

[Display omitted] • A sensitive and novel mDAIA-NFF sensor was first proposed for OA detection. • A mismatched duplexed aptamer based on conformational change for OA was designed. • A label-free RCA coupled with ThT can further enhance the detection sensitivity. • This sensor detected OA with a LOD of 3.1 ng/L and showed a good linear range. • The method is compatible with handheld fluorimeters for further great promise. We developed a highly sensitive fluorescent assay to detect okadaic acid (OA), a prevalent aquatic toxin posing serious health risks. Our approach uses a mismatched duplexed aptamer (DA) immobilized on streptavidin-conjugated magnetic beads (SMBs) to create a DA@SMB complex. In the presence of OA, the cDNA unwinds, hybridizes with a G-rich segment pre-encoding circular template (CT), and undergoes rolling circle amplification (RCA) to produce G-quadruplexes, which are detected using the fluorescent dye thioflavine T (ThT). The method has a LOD of 3.1 × 10-3 ng/mL, a linear range of 0.1 ∼ 1.0 × 103 ng/mL, and was successfully applied to shellfish samples with spiked recoveries of 85.9% ∼ 102.2% and RSD less than 13%. Furthermore, instrumental analysis confirmed the accuracy and reliability of this rapid detection method. Overall, this work represents a significant advancement in the field of rapid aquatic toxin detection and has important implications for public health and safety. [ABSTRACT FROM AUTHOR]