In this study, we report a highly stable fluorescent organic nano-chemosensor based on a N₃O₂-macrocyclic ligand. The chemosensor shows very high selectivity and sensitivity towards Fe³⁺ ions over other metal cations such as Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Ba²⁺, Al³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺, Hg²⁺ and Pb²⁺ ions in aqueous buffer solution.