Cu-Trp nanoparticle mimetic enzyme-based colorimetric immunoassay for CA19-9 detection

Highly sensitive detection of Carbohydrate Antigen 19-9 (CA19-9) is of critical importance for early cancer screening, treatment monitoring, and prognosis assessment. In this study, a colorimetric immunoassay was developed for the detection of CA19-9, utilizing Cu-Trp nanoparticles as a nanozyme. The Cu-Trp nanoparticles exhibit specific ascorbic acid oxidase-like activity, enabling the catalytic oxidation of ascorbic acid (AA) to dehydroascorbic acid (DHAA). In the presence of AA, the chromophore Fe(BPT)₃³⁺ is reduced to form a red-colored Fe(BPT)₃²⁺ complex, which exhibits a characteristic absorption peak at 534 nm. The introduction of Cu-Trp nanoparticles inhibits this colorimetric reaction by depleting AA. Based on the specific recognition between antigen and antibody, a sandwich-type colorimetric immunoassay was constructed. Under optimized conditions, a linear relationship was observed between the UV absorbance and the logarithm of CA19-9 concentration in the range of 4 to 1000 U mL^-1, with a detection limit of 0.38 U mL^-1. This analytical strategy enables highly sensitive and accurate detection of CA19-9 and holds promising potential for application in the detection of other tumor biomarkers.