Dual-metal CuFe/Fe cube nanozyme with Prussian blue analogue for highly efficient colorimetric immunoassay

Due to unique framework structures, Prussian blue analogs (PBAs) have long been of considerable interest in biosensing. However, the predominantly cubic morphology of most PBAs, along with their inherent elemental and structural limitations, restricts their catalytic performance as the nanozymes. Herein, we designed a dual-metal CuFe/Fe PBA nanozyme composite (CuFe/Fe DMPBA) exhibiting excellent peroxidase (POD)-like activity. The synthesized FePBA was prismatically loaded along the inner core CuFe PBA to build an epitaxially deposited structure. This unique architecture resulted in a substantial enhancement of the POD-like activity of the composite nanozyme compared to its individual components, FePBA and CuFe PBA. Leveraging the superior catalytic performance of the synthesized CuFe/Fe DMPBA, we further developed a highly sensitive and selective colorimetric immunoassay platform for the detection of human epidermal growth factor receptor 2 (HER2), a crucial biomarker of cancer. Under optimized conditions, this nanozyme-based immunoassay platform achieved a limit of detection (LOD) of 0.007 ng mL^-1 and a linear range from 0.01 to 10 ng mL^-1 for HER2 detection. This work not only presents a novel strategy for synthesizing high-performance PBA-based nanozymes, but also provides insights for the rational design and application of PBA materials in bioanalytical sensing.