A colorimetric and fluorescent dual-mode sensor based on bifunctional G-quadruplex-hemin complex for the...

Due to the threat of lead pollution to health, environmental and food safety, developing simple and fast detection methods is highly required. Whereas, traditional single-mode probe suffers from limited application scenario. In this study, a colorimetric and fluorometric dual-mode probe for Pb²⁺ determination was constructed by using bifunctional G-quadruplex-hemin complex. In this dual-mode probe, enzyme strand and substrate strand of 8-17 DNAzyme are labeled with G-quadruplex-hemin complex and fluorophore, respectively. In the absence of Pb²⁺, the self-assembly of enzyme strand and substrate strand inhibits intrinsic mimic peroxidase of G-quadruplex-hemin complex by base-pairing, which also quench the fluorescence via in proximity effect. When the DNAzyme is activated by Pb²⁺, the quenched fluorescence is restored as well as the inherent peroxidase mimetic activity, leading to dual signal output. Under optimal conditions, this dual-mode probe exhibit a good linear relationship between logarithm of Pb²⁺ concentration and signal difference within the range from 1.5 nM to 20 nM and 0.5 nM to 10 nM for colorimetric and fluorescence mode, respectively. The detection limits for the corresponding mode were estimated to be 1.29 nM and 0.16 nM, respectively. This dual-mode probe also successfully applied for the spiked river water assay with satisfactory recovery in the range of 93.2 %-115.3 %. This work paves a new way for DNAzyme based dual-mode probe construction.