*Communication* **A Novel Minidumbbell DNA-Based Sensor for Silver Ion Detection**

**Jiacheng Zhang 1,2,†, Yuan Liu 3,†, Zhenzhen Yan 1,2, Yue Wang 4,\* and Pei Guo 2,\***


**Abstract:** Silver ion (Ag+) is one of the most common heavy metal ions that cause environmental pollution and affect human health, and therefore, its detection is of great importance in the field of analytical chemistry. Here, we report an 8-nucleotide (nt) minidumbbell DNA-based sensor (*M-DNA*) for Ag<sup>+</sup> detection. The minidumbbell contained a unique reverse wobble C·C mispair in the minor groove, which served as the binding site for Ag+. The *M-DNA* sensor could achieve a detection limit of 2.1 nM and sense Ag<sup>+</sup> in real environmental samples with high accuracy. More importantly, the *M-DNA* sensor exhibited advantages of fast kinetics and easy operation owing to the usage of an ultrashort oligonucleotide. The minidumbbell represents a new and minimal non-B DNA structural motif for Ag<sup>+</sup> sensing, allowing for the further development of on-site environmental Ag<sup>+</sup> detection devices.

**Keywords:** DNA sensor; silver ion detection; minidumbbell; non-B DNA; C·C mismatch
