An off-on fluorescence method for acid phosphatase assay based on the inner filter effect of MnO₂ nanosheets on...

Fluorescence analysis has attracted much attention due to its rapidity and sensitivity. The present work describes a novel fluorescence detection method for acid phosphatase (ACP) on the basis of inner-filter effect (IFE), where MnO₂ nanosheets (MnO₂ NSs) and vitamin B₂ (VB₂) are served as absorbers and fluorophores, respectively. In the absence of ACP, the absorption band of MnO₂ NSs overlaps well with the excitation band of VB₂, resulting in effective IFE and inhibition of VB₂ fluorescence. In the presence of ACP, 2-phospho-L-ascorbic acid trisodium salt (AAP) is hydrolyzed to generate ascorbic acid (AA), which efficiently trigger the reduction of MnO₂ NSs into Mn²⁺ ions, causing the weakening of the MnO₂ NSs absorption band and the recovery of VB₂ fluorescence. Further investigation indicates that the fluorescence recovery degree of VB₂ increases with the increase of ACP concentration. Under selected experimental conditions, the proposed method can achieve sensitive detection of ACP in the ranges of 0.5-4.0 mU/mL and 4.0-15 mU/mL along with a limit of detection (LOD) as low as 0.14 mU/mL. Finally, this method was successfully applied for the detection of ACP in human serum samples with satisfactory recoveries in the range of 95.0 %-108 %.