A novel Tb3+-promoted G-quadruplex-hemin DNAzyme for the development of label-free visual biosensors

A Tb3+-promoted G-quadruplex-hemin DNAzyme was first reported in here. We demonstrated that trace Tb3+ is able to induce guanine-rich DNA (5′-TGGGTAGGGCGGGTTGGGAAA-3′) folding into a compact antiparallel G-quadruplex structure and thus allows the formation of G-quadruplex-hemin DNAzyme. The proposed DNAzyme can effectively catalyze the H2O2-mediated oxidation of TMB (3,3′,5,5′-tetramethylbenzidine sulfate) and leads to a change from colorless to blue in solution color, which provides a sensing platform for the label-free visual detection of Tb3+. Using above sensing platform, a selective and sensitive label-free visual method for the detection of trace Tb3+ was developed. The proposed method can be used to detect as low as 1.13 × 10−7 M of Tb3+ by the naked eyes observation and 9.0 × 10−9 M of Tb3+ by UV–vis spectrophotometry with a better stability and reproducibility. Compared with K+-promoted G-quadruplex-hemin DNAzyme reported in previous study, the novel Tb3+-promoted G-quadruplex-hemin DNAzyme has much higher peroxidase activity and better specificity, which lead to a great potential in the development of optical, electrochemical and chemiluminescence DNAzyme-based biosensors.