A Lead (II) Ion Sensor Based on Selective Recognition of G‐quadruplex for Ethyl‐substitutive Thioflavin T

Abstract

ThTÀ E (ethyl-substitutive Thioflavin T), a derivative of Thioflavin T (ThT), is capable of inducing a guanine -rich nucleic acid sequence that forms a parallel G-quadruplex under certain conditions and exhibits significant fluorescence enhancement. In this work, we used Pb 2 + to induce parallel G-quadruplex into anti-parallel G-quadruplex to reduce fluorescence of ThTÀ E and found a simple Pb 2 + detection method. Through this approach, Pb 2 + in aqueous solutions can be detected at 0. 76 nM with fluorescence spectrometry in a facile way, with high selectivity against other metal ions. These results indicate the method for detecting Pb 2 + is simple, sensitive, specific and label-free.

On-Strand Knoevenagel Insertion of a Hemicyanine Molecular Rotor Loop Residue for Turn-On Fluorescence Detection of Pb-Induced G-Quadruplex Rigidity

“…A sought-after target for GQ-sensing includes lead ion (Pb 2+ ), − which is a highly toxic heavy metal, with the ability to induce GQ-folding with superior stability compared to other common metals, such as K + and Na + . − Typical platforms are label-free (Figure A), using either GQ-specific fluorescent light-up probes − or the GQ/hemin DNAzyme complex for signal amplification. , These platforms can provide a turn-on response to Pb 2+ -binding upon formation of parallel GQ structures, ,, which contain an exposed outer G-tetrad for strong π-stacking interactions with the free dye. A turn-off response occurs when Pb 2+ -binding promotes GQ polymorphism and transitions the parallel GQ motif (favored by K + ) into an antiparallel GQ structure, which is a poor target for planar aromatic probes because their outer G-tetrads are partially shielded by lateral or diagonal loops. ,, However, GQ-sensing of Pb 2+ using such noncovalent labels presents significant challenges in real samples with coexisting metal cations, especially K + , and other molecules that can promote nonspecific GQ binding that generate false-positive outcomes …”

“…A turn-off response occurs when Pb 2+ -binding promotes GQ polymorphism 20 and transitions the parallel GQ motif (favored by K + ) into an antiparallel GQ structure, which is a poor target for planar aromatic probes because their outer G-tetrads are partially shielded by lateral or diagonal loops. 15,16,18 However, GQ-sensing of Pb 2+ using such noncovalent labels presents significant challenges in real samples with coexisting metal cations, especially K + , and other molecules that can promote nonspecific GQ binding that generate false-positive outcomes. 7 A more successful approach for GQ-sensing of Pb 2+ could involve the use of an internal covalent label that can report the structural changes mediated by Pb 2+ -binding.…”

Unlocking Pb2+ Sensing Potential in a DNA G-Quadruplex via Loop Modification with Fluorescent Chalcone Surrogates

“…A straightforward approach for Pb 2+ detection is based on GQ detection platforms, which do not require labeling and rely on the use of free fluorescent light-up probes. − The introduction of Pb 2+ triggers a topology switch from a parallel GQ or duplex to an antiparallel GQ, causing dye displacement with turn-off response. − While these methods can be useful, they often suffer from high background signals and off-target responses due to their label-free nature. Moreover, precise control of K + and Na + concentrations is required due to the lack of specificity in GQ platforms.…”