Bimodal sensor employing a novel approach for simultaneous selective detection of Ni2+ and biomolecules via turn-on fluorescence supported by DFT and molecular docking†

A bimodal sensor, (E)-2-(4-(diphenylamino)styryl)-1-methylquinolin-1-ium (DSM), was designed and synthesized for the simultaneous fluorescence turn-on detection of Ni²⁺ ion and biomolecules such as ct-DNA, BSA, and ovalbumin. Due to its distinct size and steric properties, DSM exhibits different binding modes when interacting with Ni²⁺ and DNA/proteins. The probe DSM possesses dual functionalities, allowing it to selectively detect Ni²⁺ at one binding site while interacting with ct-DNA, BSA, and ovalbumin at another. Thus, interactions of DSM with Ni²⁺ result in fluorescence enhancement at 377 nm and 400 nm, with a detection limit of 1.53 μM and binding constant of 1.2 × 10⁶ M⁻¹. Moreover, the binding of DSM with Ni²⁺ has been demonstrated via UV-vis, mass spectra, Jobs plots and DFT analysis. Conversely, binding of DSM with ct-DNA, ovalbumin and BSA led to an increase in the fluorescence at 425 nm and 435 nm, respectively, with the detection limit at micromolar (ct-DNA) and nanomolar (BSA and ovalbumin) levels. These interactions have been validated through UV-vis spectroscopy, fluorescence studies, and molecular docking analysis. Thus, this study underscores the potential of DSM as a versatile tool for simultaneous detection of both metal ions and biomolecules with a unique bimodal approach.