Unlocking Pb<sup>2+</sup> Sensing Potential in a DNA G-Quadruplex via Loop Modification with Fluorescent Chalcone Surrogates
Ryan E. Johnson, Makay T. Murray, D. Roby, Lucas J. Bycraft, Zachary R. Churcher, Saanya Yadav, Philip E. Johnson, Stacey D. Wetmore, Richard A. Manderville
Abstract
The ability of guanine (G)-rich DNA to bind toxic lead (Pb 2+ ) ions within a G-quadruplex (GQ) motif is a leading DNA biosensor strategy. A major analytical hurdle for GQ detection of Pb 2+ is competitive GQ templating by potassium (K + ) ions. We employ the on-strand DNA synthesis of internal fluorescent chalcone surrogates within the 15-mer thrombin binding aptamer (TBA15) to address this challenge. Replacement of thymidine at the 3-position (T3) within TBA15 with an indole-4-hydroxy-indanone (Ind4HI) chalcone strongly decreases K + -GQ stability while enhancing Pb 2+ -GQ stability to increase Pb 2+ binding specificity. The new T3-Ind4HI probe exhibits a 15-fold increase in fluorescence intensity upon binding of Pb 2+ by the modified TBA15 and can detect 6.4 nM Pb 2+ in the presence of 10 mM K + . Thus, replacement of the T3 residue of TBA15 with the new Ind4HI probe modulates metal ion affinity by native TBA15 to solve the analytical challenge posed by K + in real water samples for detecting Pb 2+ to meet regulatory guidelines by using a GQ biosensor.