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.