Confining copper nanoclusters in three dimensional mesoporous silica particles: Fabrication of an enhanced emission platform for "turn off-on" detection of acid phosphatase activity.

The incorporation of fluorescent nanoprobes into three dimensional (3D) matrixes is capable of enhancing the fluorescence properties of nanoprobes and greatly benefiting sensing application. In this work, N-acetyl-l-cysteine capped-copper nanoclusters (NAC-CuNCs) were incorporated into 3D mesoporous silica particles (M-SiO2) through electrostatic assembly. The assembly process takes only 2 min, and the fluorescence emission and quantum yield of NAC-CuNCs were significantly improved owing to the electrostatic confinement effect of M-SiO2. The prepared M-SiO2@NAC-CuNCs was further integrated with MnO2 nanosheets, a newly-emerged fluorescence nanoquencher with broad absorption spectrum. The emission intensity of M-SiO2@NAC-CuNCs was significantly decreased in the presence of MnO2 nanosheets by inner filter effect (IFE), and then recovered by ascorbic acid generated by the enzymolysis of l-ascorbic acid-2-phosphate (AAP) in the presence of acid phosphatase (ACP). On this basis, an enhanced emission platform was developed for "turn off-on" detection of ACP, a key indicator for diagnosis of prostate cancer. The detection limit for ACP activity was 0.47 U/L. Moreover, the approach was used to monitor ACP level in real serum samples with high accuracy, providing an attractive approach for clinical diagnosis of prostate cancer and other ACP-related diseases.