Development of an Aptamer-Based Sensing Platform for Metal Ions, Proteins, and Small Molecules through Terminal Deoxynucleotidyl Transferase Induced G‑Quadruplex Formation

We report a label-free, structure-independent luminescent-sensing platform for metal ions, proteins, and small molecules utilizing an Ir­(III) complex, terminal deoxynucleotidyl transferase (TdT), and a structure-folding aptamer. A novel G-quadruplex-selective Ir­(III) complex was identified to detect the nascent G-quadruplex motifs with an enhanced luminescence response. Unlike most label-free DNA-based assays reported in the literature, this sensing platform does not require a specific secondary structure of aptamer, thus greatly simplifying DNA design. The detection platform was demonstrated by the detection of K<sup>+</sup> ions, thrombin, and cocaine as representative examples of metal ions, proteins, and small molecules.