A novel Tb(3+)-promoted G-quadruplex-hemin DNAzyme for the development of label-free visual biosensors

A Tb(3+)-promoted G-quadruplex-hemin DNAzyme was first reported in here. We demonstrated that trace Tb(3+) 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 H(2)O(2)-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 Tb(3+). Using above sensing platform, a selective and sensitive label-free visual method for the detection of trace Tb(3+) was developed. The proposed method can be used to detect as low as 1.13×10(-7) M of Tb(3+) by the naked eyes observation and 9.0×10(-9) M of Tb(3+) by UV-vis spectrophotometry with a better stability and reproducibility. Compared with K(+)-promoted G-quadruplex-hemin DNAzyme reported in previous study, the novel Tb(3+)-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.