A colorimetric immunoassay based on cobalt hydroxide nanocages as oxidase mimics for detection of ochratoxin A.

Oxidase nanozymes have attracted particular attention in colorimetric immunoassay due to their high activity, stability, and biocompatibility. In this work, the well-dispersed Co(OH)2 nanocages were synthesized by a template-assisted strategy. The prepared Co(OH)2 nanocages exhibited an intrinsic oxidase-like activity, which can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) without the addition of hydrogen peroxide (H2O2). Hence, a simple and sensitive colorimetric immunoassay was established to detect ochratoxin A (OTA). In this immunosensor, the microplates were modified with dopamine as the substrate to capture antigens. Then, the uniform Co(OH)2 nanocages were used as the vehicle to carry the secondary antibody for the recognition of immunoreaction. The sensing system can generate color responses with the OTA concentration in the range from 0.5 ng/L to 5 μg/L, and the detection limit was as low as 0.26 ng/L. Therefore, as a nano-artificial enzyme, Co(OH)2 nanocages may show promising potential in visual detection of the real samples.