Copper ion as a peroxidase mimic for fluorescent detection of casein phosphopeptide by a 3D-printed portable device

Developing an on-site sensing platform for casein phosphopeptide (CPP) is essential to ensure the quality of infant formula. This study is the first report on a fluorescence detection method for CPP. The method is based on the readily available copper ions (Cu 2+ ). Cu 2+ has peroxidase-like activity and can catalyze the oxidation of o -phenylenediamine (OPD) to produce 2,3-diaminophenazine with a fluorescence property. CPP can inhibit the peroxidase activity of Cu 2+ through the coordination of the phosphate groups in CPP and suppress the oxidation of OPD, decreasing the fluorescence intensity of the catalytic system. Based on this principle, a fluorescence approach was developed to detect CPP in milk and milk powder samples. The method does not require the preparation of nanomaterials, and the detection process takes 25 min. Furthermore, a self-designed portable detection device was constructed to detect CPP, demonstrating the potential of the fluorescence sensing platform in the on-site detection of CPP.