Copper nanoclusters@Al³⁺ complexes with strong and stable aggregation-induced emission for application in enzymatic...

The aggregates of glutathione-capped CuNCs induced by Al³⁺ (named CuNCs@Al³⁺ complexes) show a stable aggregation-induced emission (AIE) for about 1 month. Their fluorescence maintains a high level in the pH range 4.0 to 7.0, while it quenches as pH increases from 7.0 to 7.7 or decreases from 4.0 to 3.0. Under urease-catalyzed hydrolysis, urea produces ammonia, which can be further hydrolyzed to yield OH^-. This leads to a pH increase of the immediate environment. Hence, the CuNCs@Al³⁺ complexes are a suitable probe to determine urea. The fluorescence of CuNCs@Al³⁺ complexes quenches linearly at 585 nm with the excitation wavelength at 340 nm when the concentration of urea increases from 20 to 150 μM. The limit of detection (LOD) of urea is 5.86 μM. This sensitivity is superior to other reported works due to the narrow pH response range of CuNCs@Al³⁺ complexes. This method has been successfully applied for measuring urea in human urine samples with satisfactory recoveries. Graphic abstract Schematic representation of urea determination based on pH-responsive property of copper nanoclusters@Al³⁺ complexes. Ammonia is produced in the hydrolysis of urea by urease, and it is further hydrolyzed to yield OH^-, leading to increasing pH of the environment.