Selection of DNA Aptamers for Sensing Uric Acid in Simulated Tears

Abstract

Uric acid is a biomarker for a range of diseases and hyperuricemia is the cause of many diseases including gout. While most biosensors for detecting uric acid relied on enzymatic reactions, in this work a library-immobilization method was used to obtain DNA aptamers for uric acid. After 18 rounds of selection, two representative aptamers were obtained with a Kd around 1.2 μM measured by isothermal titration calorimetry (ITC). Based on their difference in binding to xanthine, which differs from uric acid by only one oxygen atom, these two aptamers have different binding orientations to uric acid. ITC also indicated that the UA-1 aptamer specifically required a high concentration of Na+ for binding, which cannot be replaced by Li+, K+ or Mg2+. Combined ITC and fluorescence spectroscopy data indicated the need of three Na+ ions, which explained the requirement of a high Na+ concentration. The UA-1 aptamer was engineered into a fluorescent biosensor based on the strand-displacement reaction, resulting in a limit of detection of 90 nM uric acid. This sensor was also tested in simulated tears with a limit of detection of 350 nM uric acid.