A DNA Aptamer for 2-Aminopurine: Binding-Induced Fluorescence Quenching

2-Aminopurine (2AP) is a fluorescent analog of adenine, and its unique properties make it valuable in various biochemical and biotechnological applications. Its fluorescence property probes local dynamics in DNA and RNA because stacking with the surrounding bases quench its fluorescence. 2AP-labeled DNA or RNA sequences have been used for the detection of genetic mutations, viral RNA, or other nucleic acid-based markers associated with diseases like cancer and infectious diseases. In this study, we isolated aptamers for 2AP using the library immobilization capture-SELEX technique. A dominating aptamer family was isolated after 15 rounds of selection. The K_d values for the most abundant 2AP1 aptamer are 209 nM in a fluorescence assay and 72 nM in an isothermal titration calorimetry test. A 32 nM 2AP limit of detection was tested based on its intrinsic fluorescence change upon aptamer binding. Additionally, we conducted some mutation analysis. Furthermore, we tested the selectivity of this aptamer and discovered that it can bind adenine and adenosine with approximately 100-fold lower affinity than 2AP.