A new fluorescent PET sensor probe for Co2+ ion detection: computational, logic device and living cell imaging applications

Abstract

The hydrophobic nature of β-cyclodextrin (β-CD) increases the solubility and stability of 1,2-dihydroxyanthraquinone (1,2-DHAQ; 1) and hence permits the coordination of 1 with cations in aqueous solution; this has been investigated by means of UV-visible and fluorescence spectroscopy. β-CD:1,2-DHAQ (2) demonstrates colorimetric recognition behavior toward Co²⁺ ion by changing the color of the solution, which can be easily detected with the naked eye. The chemosensor 2 showed good fluorescence behavior upon interaction with various cations; it displayed strong fluorescence quenching (Co²⁺; ∼80% switch-off) as a fluorescent chemosensor based on photoinduced electron transfer (PET). Moreover, when the 2·Co²⁺ complex was tested with various anions, only nitrate (NO₃⁻) enabled cobalt binding (as CoNO₃) and led to fluorescence enhancement (∼82%; switch-on). The detection limits of sensor 2 with Co²⁺ and NO₃⁻ were found to be 22.7 nM and 2.4 nM. Theoretical molecular docking studies and density functional theory (DFT) calculations were performed to study the binding of Co²⁺ and NO₃⁻ ions with 2. The changes in the fluorescence of 2 upon addition of Co²⁺ followed by NO₃⁻ can be utilised as an XNOR logic gate. Furthermore, 2 has potential for use in bio-imaging as a fluorescent probe to detect Co²⁺ ion, followed by sequential detection of NO₃⁻ ion by 2·Co²⁺, in living cells (human cervical cancer HeLa cell line) using confocal laser scanning microscopy.