Efficient Fluorescence Turn-On Probe for Zirconium via a Target-Triggered DNA Molecular Beacon Strategy

It is well-known that Zr4+ could selectively bind with two phosphate-functionalized molecules through a coordinate covalent interaction to form a sandwich-structured complex (-PO32--Zr4+-PO32--). In this paper, we for the first time converted such interaction into fluorescence sensing systems for Zr4+ via a target-triggered DNA molecular beacon strategy. In the new designed sensing system, two phosphorylated and pyrene-labeled oligonucleotides were chosen as both recognition and reporter units, which will be linked by target Zr4+ to form a hairpin structure and bring the two labeled pyrene molecules into close proximity, resulting in a "turn-on" excimer fluorescence signal. Moreover, gamma-cyclodextrin was introduced to afford an amplified fluorescence signal and, therefore, provided an improved sensitivity for the target Zr4+. This allows detection of Zr4+ with high sensitivity (limit of detection, LOD = 200 nM) and excellent selectivity. The proposed sensing system has also been used for detection of Zr4+ in river water samples with satisfactory result.