A pH-responsive bioassay for sensitive colorimetric detection of adenosine triphosphate based on switchable DNA aptamer and metal ion–urease interactions

A facile and economic colorimetric strategy was designed for ATP detection by rationally using urease, a pH-responsive molecule, and a metal-mediated switchable DNA probe. By utilizing metal ions as a modulator of urease activity, the concentration of ATP is translated into pH change, which can be readily visualized by naked eye. An unmodified single-stranded DNA probe was designed, which consists of a target binding sequence and two flanked cytosine (C)-rich sequences. This C-rich single-stranded DNA can form a hairpin structure triggered by Ag+ ions via C-Ag+-C base mismatch. Upon introduction of ATP, Ag+-coordinated hairpin DNA structure will be broken and release the included Ag+, thus inhibiting the activity of urease. Conversely, urease can hydrolyze urea and raise pH value of the solution, resulting in the color change of the sensing solution. The proposed assay allows determination of ATP as low as 1.6 nM and shows a satisfactory result in human serum. Because of simple operation and low cost of this method, we believe it has a potential in point-of-care (POC) testing in resource-limited areas.