Label-free and sensitive detection of coralyne and heparin based on target-induced G-quadruplex formation

Herein we propose a label-free and sensitive detection method for coralyne and heparin, based on utilizing the complex of adenosine₁₆ (A₁₆) and coralyne to induce the formation of a G-quadruplex scaffold. In the present work, two specific oligonucleotide strands were designed. Upon addition of coralyne, the two oligonucleotide strands formed a double chain through A₂–coralyne–A₂ coordination, which induced the formation of an intermolecular G-quadruplex accompanied by the proximity of two G-rich sequences. An increase in system fluorescence was observed after the addition of N-methylmorpholine (NMM). In the presence of heparin, the formation of the heparin–coralyne complex caused coralyne to be removed from the A₁₆–coralyne complex, leading to a weaker fluorescence output. At optimal concentrations, a linear coralyne response could be observed from 0.01–5 μM and the detection limit was estimated to be 5.8 nM. The detection limit of the heparin probe was as low as 1 nM, with a linear range from 1–100 nM. Overall, this study offers a sensitive and practical assay for coralyne and heparin detection.