This work shows the sodium citrate induced efficient interpolymer π-stacking aggregation of the planar cationic conjugated polyelectrolyte poly[{9,9-bis[6'-(N,N-trimethylamino)hexyl]-2,7-fluorenyleneethynylene}-alt-co-(1,4-phenylene)] dibromide (PFE) in aqueous solution, which results in the self-quenching of fluorescence. Using the citrate-induced aggregation properties of PFE and the strong chelation ability of citrate with aluminum ions (Al(3+)), a sensitive and selective Al(3+)-ion detection assay in aqueous solution was developed through monitoring of the fluorescence recovery of PFE. The fluorescence intensity recovery of PFE depends on the concentration of Al(3+) ions, and linear fluorescence recovery was observed in the range of 0.5-9 μM. The limit of detection of this assay is 0.37 μM. Its simplicity and rapidity mean this assay shows promise for the real-time detection of Al(3+).