<p>A hemicyanine-based colorimetric and fluorometric sensor, 2-(2-(2,3,5,6,8,9-hexahydrobenzo[b][1,4,7,10]tetraoxacyclododecin-12-yl)vinyl)-3,3-dimethyl-1-propyl-3H-indol-1-ium iodide (MH-5), was developed and synthesized to detect Li⁺ and CN⁻ ions in DMSO-PBS buffer solution (10&#xa0;mM, pH 7.25, v/v 1:9). MH-5 displayed a rapid and highly selective colorimetric response to both Li⁺ and CN⁻, indicated by a distinct color change from pink to pale pink in the presence of Li⁺ and to colorless upon CN⁻ detection, without interference from other cations or anions. The interaction mechanisms of MH-5 with Li⁺ and CN⁻ ions were investigated using various analytical techniques, including ¹H NMR, ESI–MS, FT-IR spectroscopy, and Job’s plot analysis. These studies suggest that CN⁻ is detected through nucleophilic addition to the indolium moiety of MH-5, while Li⁺ detection occurs via coordination with oxygen atoms in the crown ether structure. The fluorescence-based detection limits for Li⁺ and CN⁻ were determined to be 0.150&#xa0;µM and 0.154&#xa0;µM, respectively. Additionally, MH-5 was evaluated in living cells, demonstrating effective cell penetration and reliable detection of Li⁺ and CN⁻ ions for potential bio-imaging applications.</p> Graphical Abstract <p></p>