Potassium cobalt hexacyanoferrate as a peroxidase mimic for electrochemical immunosensing of Lactobacillus rhamnosus GG

In this paper, the potassium cobalt hexacyanoferrate (II), K 2 CoFe(CN) 6 , with peroxidase-like activity was used for the fabrication of a novel label-free Lactobacillus rhamnosus GG (LGG) electrochemical immunosensor. The K 2 CoFe(CN) 6 nanocubes were made by a simple hydrothermal method and followed by low-temperature calcination. In addition to structural characterization, the peroxidase-mimicking catalytic property of the material was confirmed by a chromogenic reaction. It is known that H 2 O 2 can oxidize electroactive thionine molecules under the catalysis of horseradish peroxidase (HRP). In this nanozyme-based electrochemical immunoassay , due to the steric hindrance , the formation of immune-complex of LGG and LGG antibody on the modified GCE inhibits the catalytic activity of the peroxidase mimics of K 2 CoFe(CN) 6 and thus reduced the current signal. Therefore, the developed electrochemical immunosensor achieved quantitative detection of LGG. Under optimal conditions, the linear range of the sensor was obtained from 10 1 to 10 6  CFU mL −1 with a minimum detection limit (LOD) of 12 CFU mL −1 . Furthermore, the immunosensor was successfully applied in the quantitative detection of LGG in dairy product samples with recoveries ranging from 93.2% to 106.8%. This protocol presents a novel immunoassay method , which provides an alternative implementation pathway for the quantitative detection of microorganisms.