Partially Phosphidated Prussian Blue Analogues Derived Heterostructure Nanozyme for Colorimetric-Photothermal Dual-Mode Immunoassay

Colorimetric and photothermal sensing platforms based on nanozymes are attractive because of their simplicity, yet their sensitivity is often limited by insufficient catalytic performance. Herein, we reported a nanozyme-based strategy regulated by controlled partial phosphidation to enhance colorimetric and photothermal signal transduction. Through an etching-doping-partial phosphidation (E-D-P) strategy, polymetallic phosphide nanoparticles were in situ generated and embedded within tannic acid-etched and Cu2+-doped CoPBA nanocages, forming a phosphide-Prussian blue analogue (PBA) hybrid heterostructure. Owing to polymetallic composition and the PBA-derived structure, the resulting CuCo-P@PBA nanozyme exhibited efficient peroxidase (POD)-like catalytic activity toward the 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2 system, with a high maximum reaction velocity and a low Michaelis constant, enabling effective catalytic signal amplification. Attributed to the catalytic efficiency of the CuCo-P@PBA nanozyme, a dual-mode immunosensing platform integrating colorimetric and photothermal readouts was constructed. The colorimetric mode exhibited a linear response over 0.005-50 ng mL-1 with a limit of detection (LOD) of 3.4 pg mL-1, while the photothermal mode provided a linear range of 0.01-50 ng mL-1 with an LOD of 4.0 pg mL-1. The colorimetric response at 652 nm and photothermal signal under 808 nm irradiation provided two correlated signal outputs. The platform enables sensitive determination of human epidermal growth factor receptor 2 (HER2) with a wide linear range and good agreement with a commercial enzyme-linked immunosorbent assay (ELISA) in clinical serum samples, highlighting its potential for reliable bioanalytical sensing.