Salt-Toggled Capture Selection of Uric Acid Binding Aptamers.

Uric acid is the end-product of purine metabolism in humans and an important biomarker for many diseases. To achieve the detection of uric acid without using enzymes, we previously selected a DNA aptamer for uric acid with a K d of 1 μM but the aptamer required multiple Na + ions for binding. Saturated binding was achieved with around 700 mM Na + and the binding at the physiological condition was much weaker. In this work, a new selection was performed by alternating Mg 2+ -containing buffers with Na + and Li + . After 13 rounds of selection, a new aptamer sequence named UA-Mg-1 was obtained. Isothermal titration calorimetry confirmed aptamer binding in both selection buffers, and the K d was around 8 μM. The binding of UA-Mg-1 to UA required only Mg 2+ . This is an indicator of successful switching of metal dependency via the salt-toggled selection method. The UA-Mg-1 aptamer was engineered into a fluorescent biosensor based on the strand-displacement assay with a limit of detection of 0.5 μM uric acid in the selection buffer. Finally, comparison with the previously reported Na + -dependent aptamer and a xanthine/uric acid riboswitch was also made.