Colorimetric detection of ascorbic acid and alkaline phosphatase activity based on the novel oxidase mimetic of Fe-Co bimetallic alloy encapsulated porous carbon nanocages.

A novel catalyst of FeCo nanoparticles (FeCo NPs) incorporated porous nanocages (FeCo NPs@PNC) was first synthesized by encapsulating of FeCo alloy into ZIF-8 and further carbonation of the composite. The FeCo NPs@PNC displays enhanced intrinsic oxidase-like activity compared to the individual FeCo NPs and porous nanocages (PNC). The FeCo NPs@PNC can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to oxidized TMB (oxTMB) without HO, producing a blue color with a maximum absorption peak at 652 nm. The catalytic mechanism was investigated and it found that the intermediate (O) produced from the catalytic process in the system of TMB-O-FeCo NPs@PNC can accelerate the oxidation of TMB to oxTMB. However, ascorbic acid (AA) can reduce the oxTMB and result in a conspicuous blue color fading. Therefore, a novel colorimetric platform was constructed to quantify AA with the linear range of 0.5-28 μM and detection limit of 0.38 μM (at 3σ/m). Owing to the alkaline phosphatase (ALP) can catalyze the hydrolysis of AA 2-phosphate (AAP) into AA, ALP can also be quantified by the above method. And the linear range for ALP is 0.6-10 U L and the limit of detection is 0.49 U L. The FeCo NPs@PNC also shows excellent stability and reproducibility. This study provides a new alternative oxidase mimetic on the basis of easily obtained metal-organic frameworks derivatives to replace the expensive natural enzymes and noble metal based nanoenzymes, which will show great potential in biological assays.