Development of a Fluorescent Probe for Specific Visualization of Intracellular DNA i-Motif Participating in Key Biological Function.

The i-motif structure has received increasing interest due to its significant biological function discovered in recent years. However, the absence of a handy and efficient method for visualizing the i-motif limited its intracellular study. Herein, we report an innovative coumarin-carbazole-based fluorescent probe, , for intracellular detection of i-motif. exhibited excellent i-motif recognition ability and selectivity. By using , we successfully visualized the ribosome DNA (rDNA) i-motif within the nucleoli. Our results revealed the colocalization of rDNA i-motif with RNA polymerase I, and their separation under drug-induced nucleolar stress, suggesting that rDNA i-motif could play a regulatory role in rDNA transcription. was also well applied for the detection of the i-motif in live cells and zebrafish juveniles, which could become an important tool for studying its biological function. As we know, this is the first discovery and development of a small-molecule fluorescent probe for specific visualization of i-motif in cells and , providing its direct evidence of participating in key biological function.