A Highly Sensitive Benzimidazole‐DNA‐Based Biosensor for Intracellular Detection of Cu ²⁺ Through a Ternary Complex Formation

Abstract We report here highly sensitive Cu 2+ ion sensing properties of a DNA oligomer‐based biosensor developed from a benzimidazole derivative. The synthesized guanidinylated benzimidazole (compound 6 ) was first screened against various nucleic acid structures to identify the nucleic acid where it afforded the highest fluorescence emission response. The DNA oligomer‐compound 6 biosensor, thus prepared was used to screen a variety of metal ions. The best sensing abilities were observed for Cu 2+ ions, which were conspicuous through their significant quenching of the biosensor's fluorescence. Interference studies suggested the robustness of the sensing results, which were further investigated using UV–vis and CD spectroscopic techniques to find a possible clue toward the mechanism involved in the sensing process. Both techniques suggested the possible formation of a ternary complex involving the DNA, compound 6 , and the Cu 2+ ions, which leads to the quenching of fluorescence. The limit of detection (LoD) for Cu 2+ ions was found to be 37 ppb. The application of this sensor was then checked in real samples, which showed approximately 100% recovery of Cu 2+ ions in each case. Finally, we checked the application of this biosensing process in cellular medium using HEK293T cells, where Cu 2+ quenching effect was observed on the expected lines.