Effect of different crystal forms of MnO2 quenchers on the sensitivity of copper nanoclusters and their use in acidphosphatase activity.

Highly stable copper nanocluster (CuNCs) with aggregation-induced emission (AIE) properties was synthesized. α-, β-, and γ- MnO2 were utilized as quenchers, with CuNCs fluorescence quenching of 48.9%, 91.5%, and 96.6%, respectively. L-ascorbate-2-phosphate (AAP) was hydrolyzed by acid phosphatase (ACP), and ascorbic acid (AA) was formed. Then, MnO2 could be restored by AA, and the fluorescence of the CuNCs could be restored. An on-off-on detection platform with a high signal/noise ratio was constructed for the sensing of ACP. The fluorescence recovery rate of the CuNCs was related to the crystal forms of MnO2. Then, the equilibrium constants (K) for the reaction between AA and MnO2 were calculated to evaluate the reaction process. Compared with the K values of CuNCs/α-MnO2 and CuNCs/γ-MnO2, the K values for AA and β-MnO2 were maximum. The CuNCs/β-MnO2 system exhibited optimal fluorescence recovery for the sensitive detection of ACP. In the concentration range 0.005-0.06 U/mL, the detection limit was 0.0028 U/mL. The determination  of serum ACP levels also revealed satisfactory results. This study provides novel insights into enhancing the sensitivity of the determination  of quenchers in different crystal form.