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The hydrophobic nature of b-cyclodextrin (b-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. b-CD:1,2-DHAQ (2) demonstrates colorimetric recognition behavior toward Co 2+ 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 (Co 2+ ; $80% switch-off) as a fluorescent chemosensor based on photoinduced electron transfer (PET).Moreover, when the 2$Co 2+ complex was tested with various anions, only nitrate (NO 3 À ) enabled cobalt binding (as CoNO 3 ) and led to fluorescence enhancement ($82%; switch-on). The detection limits of sensor 2 with Co 2+ and NO 3 À were found to be 22.7 nM and 2.4 nM. Theoretical molecular docking studies and density functional theory (DFT) calculations were performed to study the binding of Co 2+ and NO 3 À ions with 2. The changes in the fluorescence of 2 upon addition of Co 2+ followed by NO 3 À can be utilised as an XNOR logic gate. Furthermore, 2 has potential for use in bio-imaging as a fluorescent probe to detect Co 2+ ion, followed by sequential detection of NO 3 À ion by 2$Co 2+ , in living cells (human cervical cancer HeLa cell line) using confocal laser scanning microscopy.These studies suggest that the use of uorescent chemosensors ; Tel: +91 9944266475 † Electronic supplementary information (ESI) available. See Scheme 1 Chemical structure of 1,2-DHAQ.16582 | RSC Adv., 2017, 7, 16581-16593This journal is