A new two-dimensional (2D) bio-metal-organic framework based on trinuclear cluster units, [Zn₃(adeninate)₂(CH₃COO)₄]∙DMF (Zn–A), was synthesized by the self-assembly of biomolecule adenines with zinc ions. Topological analysis reveals its 4⁴ connected layer structure. Remarkably, Zn–A bears high sensitivity and selectivity detection ability of iron ion with the limit of detection being 4.0 × 10^-6 mol/L.