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A new method has been developed for the simple, fluorescence, turn-on detection of melamine, which utilizes DNA-templated silver nanoclusters (DNA-AgNCs) as a key component. In the sensor, melamine exhibits the dual functions: one is to enhance the fluorescence signal of DNA-AgNCs by its specific interaction with thymine residues in DNA template, and the other is to prevent Hg(II)-induced fluorescence quenching of DNA-AgNCs via its strong coordination with Hg(II). These consequently enable the sensitive and selective detection of melamine. By exploiting such novel features of melamine, we significantly increased the fluorescence response up to 360%, compared to the previous counterpart that relies on DNA-AgNCs only, and successfully determined melamine down to ca. 49 nM, a value that is 400 times lower than the safety level of 20 μM set by the US Food and Drug Administration. In addition, it was confirmed that the proposed approach works fine even in the real milk samples without any additional pre-treatment steps. [ABSTRACT FROM AUTHOR]

A simple, sequence-specific DNA detection method, utilizing a fluorescent 2-aminopurine (2-AP) nucleobase analogue-containing split G-quadruplex as the key detection component, is described. In the sensor, the 2-AP-containing G-quadruplex is split into two segments and linked to a target-specific overhang sequence. The separate G-quadruplex sequences form an active G-quadruplex structure only in the presence of a complementary target DNA, which leads to a significant increase in the intensity of fluorescence from the 2-AP fluorophore. This simple, one-step, homogenous assay was successfully employed to detect target DNA with a high selectivity. In addition, the practical applicability of the detection method was demonstrated by its use in analyzing target DNAs in human serum. To the best of our knowledge, this is the first time that an investigation was carried out in which a fluorescent nucleobase analogue was incorporated into a split G-quadruplex structure and this structure was utilized as the foundation for a specific DNA sensor. [ABSTRACT FROM AUTHOR]