Perylene ligand wrapping G-quadruplex DNA for label-free fluorescence potassium recognition

A perylene ligand, N,N-bis-(1-aminopropyl-3-propylimidazol salt)-3,4,9,10-perylene tetracarboxylic acid diimide ligand (PDI), which consisted of π-conjugated perylene moiety and hydrophilic side chains with positively charged imidazole rings, was used to wrap G-quadruplex for fluorescence turn-on K+ recognition. Electrostatic attraction between PDI's positively charged imidazole rings and DNA's negatively charged phosphate backbones enabled PDI to accumulate on DNA. Upon trapping K+, these G-rich DNA sequences transitioned to G-quadruplex. Subsequently, PDI ligands wrapped G-quadruplex, in which the flat aromatic core of PDI ligand interacted with G-quartet through π–π stacking and the side chains were positioned in grooves through electrostatic interactions. Consequently, the interaction mode change and conformational transition from PDI stacked G-sequence to PDI wrapped G-quadruplex led to PDI fluorescence enhancement, which was readily monitored as the detection signal. This strategy excluded the sequence tagging step and exhibited high selectivity and sensitivity towards K+ ion with the linear detection range of 10–150 nM. Besides, PDI ligands may hold diagnostic and therapeutic application potentials to human telomere and cancer cells.

► Upon trapping K+, G-rich DNA sequences transitioned to G-quadruplex.
► Conformation changed from PDI stacked G-sequence to PDI wrapped G-quadruplex.
► Fluorescence enhancement of PDI was observed.
► Fluorescent K+ recognition with high sensitivity and selectivity was achieved.