Input-dependent induction of G-quadruplex formation for detection of lead (II) by fluorescent ion logic gate

Abstract

A label-free fluorescent AND logic gate has been developed utilizing ion-tuned configuration conversion of DNA probe with K+ and Pb2+ as two inputs. A well-designed hairpin DNA which is composed of a poly-G loop and a GR-5 DNAzyme stem serves as a recognition probe, and an derivative of aloe-emodin (AED) was designed and synthesized as signal probe. In the presence of Pb2+, the substrate strand of DNAzyme is irreversibly and specifically cleaved at the cleavage site, which made the poly-G loop form G-quadruplex in the presence of a constant concentration of K+. Such a structural change significantly affects the spectral behaviors of AED, which can be explored to ultra-sensitively detect Pb2+ with a limit of detection of 22.8pM. By combing the high specificity of hairpin DNA and GR-5 DNAzyme, Pb2+ can be highly selectively detected even when coexisted with other metal ions. Circular dichroism (CD), UV–vis absorption spectrometry and fluorescence polarization (FP) measurements further verified the reliability and reasonability of the sensing mechanism. Therefore, it provides a simple and label-free approach to detect ions with high sensitivity and specificity, and promises to provide a solid sensing platform for the detection of targets by altering the specific sequence of nucleic acid probe.