<p>This study describes the synthesis and characterization of aluminium metal‒organic framework (Al‒MOF) using trimesic acid and succinic acid linkers and fluorescein functionalized aluminium metal‒organic framework (FL@Al-MOF) as sensor for heavy metal ion detection. The structure, crystallinity, porosity and thermal stability of the synthesized Al-MOF were confirmed by employing FT-IR, HR-TEM, PXRD, FE-SEM, EDX, XPS, BET, and TGA analyses. FL@Al-MOF, the functionalized Al-MOF using Fluorescein (FL) as a luminescent guest was done via post-synthetic modification. The FL@Al-MOF showed high sensitivity and strong fluorescence quenching toward heavy metal ions, namely Pb²⁺, Cd²⁺, and Hg²⁺. With detection capabilities ranging from 0.05 µM to as low as 0.002 µM at room temperature, fluorescence quenching studies demonstrated a significant and concentration-dependent indicated sensitivity and selectivity of response. The LOD (Limit of Detection) and LOQ (Limit of Quantification) data FL@Al-MOF for Hg²⁺ ions. This study highlights synthesis and characterization of aluminium metal-organic framework (Al-MOF) and its functionalization with fluorescein (FL@Al-MOF) for heavy metal ion sensing. This research reports a promising metal–organic framework-based sensor with potential uses in environmental applications and remediation for the trace-level detection of heavy metal contaminants.</p>