Fe-N hollow mesoporous carbon spheres with high oxidase-like activity for sensitive detection of alkaline phosphatase

Due to the vital role of alkaline phosphatase (ALP) in clinical diagnoses and biomedical research, a sensitive and selective detection method for ALP activity is of considerable importance. Herein, a facile and sensitive colorimetric assay for the detection of ALP activity was developed based on Fe-N hollow mesoporous carbon spheres (Fe-N HMCS). Fe-N HMCS were synthesized by a practical one-pot method with aminophenol/formaldehyde (APF) resin as the carbon/nitrogen precursor, silica as the template and iron phthalocyanine (FePC) as the iron source. Thanks to the highly dispersed Fe-N active sites, Fe-N HMCS exhibited exceptional oxidase-like activity. In the presence of dissolved oxygen, Fe-N HMCS were able to effectively convert colorless 3,3',5,5'-tetramethylbenzidine (TMB) into oxidized TMB (oxTMB) with blue color, while the reducing agent of ascorbic acid (AA) inhibited the color reaction. Based on this fact, an indirect and sensitive colorimetric sensing method was developed to detect alkaline phosphatase (ALP) with the assistance of the substrate L-ascorbate 2-phosphate (AAP). This ALP biosensor exhibited a linear range of 1-30 U L^-1 and a limit of detection (LOD) of 0.42 U L^-1 in standard solutions. In addition, this method was applied to detect ALP activity in human serum with satisfactory results. This work offers a positive reference for the reasonable excavation of transition metal-N carbon compounds in ALP-extended sensing applications.