Transition Metal Dependent Binding of Tannic Acid by a DNA Aptamer

Tannic acid (TA) is a natural polyphenol composed of multiple galloyl groups. TA is known for its antioxidation and metal-coordination properties. While some methods exist for the detection of TA, they are often susceptible to interference by other antioxidants or metal chelators. In this regard, we herein used a library-immobilization based method to obtain several TA-binding aptamers, including TA-15. The TA-15 aptamer binds to TA with a dissociation constant (K_d) of 0.4 μM, in an enthalpy-driven, Mg²⁺-independent manner as determined using isothermal titration calorimetry (ITC). TA-15 does not bind to oxidized TA or 12 other small molecules including gallic acid, indicating high specificity. A fluorescent strand-displacement assay was designed based on TA-15, producing a fluorescence enhancement upon TA binding with an apparent K_d of 0.32 μM, and a detection limit of 4.8 nM. Several transition metals inhibited TA binding, whereas EDTA effectively restored binding by chelating these metals. With EDTA, detection of TA in tap water and wastewater was achieved. This study has generated the first biomolecule for selective binding to TA. Beyond sensing, it enables opportunities in antioxidant analysis, environmental monitoring, TA separation, and preparing DNA/TA complex materials for drug delivery.