Visual detection of acid phosphatase based on hollow mesoporous manganese dioxide nanospheres

Acid phosphatase is widely used as a clinical indicator because of its close correlation with a variety of diseases. Herein, a label-free and colorimetric sensing method for detecting the activity of acid phosphatase was constructed based on hollow mesoporous manganese dioxide nanospheres. The nanospheres exhibit superior oxidase-like property and can oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to yellow TMB²⁺. Ascorbic acid from acid phosphatase-catalyzed hydrolysis of L-ascorbic acid-2-phosphate will inhibit the oxidization reaction, igniting vivid color variation. On the basis of this obvious multicolor change, the visual detection of acid phosphatase was achieved. Compared with the single-color change, the multicolor colorimetric method is more conducive for naked-eye discrimination. The absorbance difference at 450 nm exhibits a linear relationship with the concentration of acid phosphatase ranging from 1.0 to 25 U L^-1, with a detection limit as low as 0.45 U L^-1. Acid phosphatase in human serum samples was successfully determined. Moreover, the inhibition efficiency of NaF for acid phosphatase activity was investigated, proving the proposed colorimetric method will be a potential platform for screening acid phosphatase inhibitors and discovering new drugs.