A ratiometric fluorescence platform for lead ion detection via RNA cleavage-inhibited self-assembly of three-arm branched junction.

Heavy metal pollution can pose a threat to food safety and human health, and accurate quantification of heavy metal ions is a vital requirement. Emerging DNA nanostructures-based biosensors offer attractive tools toward ultra-sensitive or rapid analysis of heavy metal ions. However, the problems including complex design, severe reaction conditions and undesirable reliability are inevitable obstacle in advancing their extension and application. Herein, a ratiometric fluorescent platform was established for monitoring lead ion (Pb) in food based on dual Förster resonance energy transfer (FRET) and RNA cleavage-inhibited self-assembly of three-arm branched junction (TBJ). GR-5 DNAzyme was employed for Pb recognition, and enzyme-free amplification technique catalytic hairpin assembly (CHA) served to form FRET probes-carried TBJ. The substrate strand (S) of DNAzyme triggered the generation of CHA-TBJ, and Pb-responsive cleavage of S hindered the assembly of CHA-TBJ, causing opposite changes in the FRET states of FAM/BHQ1 and ROX/BHQ2 pairs. The fluorescence responses were recorded through synchronous fluorescence spectrometry to indicate Pb concentration, allowing sensitive and reliable identification of Pb in the linear range of 0.05-5 ng mL with the detection limit of 0.03 ng mL. The Pb detection can be achieved under conventional reaction conditions, simple mixing procedures and one-step measurement operation. The approach can afford excellent specificity for Pb against competing metal ions, and can be applied to analyze Pb in tea samples with satisfactory results. This facile fluorescence platform shows a capable method for Pb detection, and provides new avenue in the development of ratiometric approaches and DNAzyme strategies for monitoring heavy metal pollution, facilitating the transformation of DNAzyme-based biosensors for food safety control.