A pH-responsive dual-enzyme nanozyme based on nitrogen-doped carbon-supported CoFe2O4 for dopamine colorimetric sensing

N-doped carbon/CoFe₂O₄ nanozyme with pH-switchable POD/CAT activity from PBA precursor. • Enables sensitive colorimetric DA detection at pH 3–11 with LODs of 0.0179/0.0488 μM. • High selectivity and recovery (90–103%) in serum show potential for bioanalysis and POC diagnostics. In this work, the design and synthesis of a pH-responsive dual-enzyme nanozyme based on nitrogen-doped carbon-supported CoFe 2 O 4 spinel (C(N)@CoFe 2 O 4 ) derived from cobalt-doped Prussian blue analogues (PBAs) has been reported. The material was obtained through controlled calcination, with the 500 °C sample (C(N)@CoFe 2 O 4 _500) exhibiting high crystallinity, a large specific surface area (256.30 m 2 ·g −1 ), and uniform distribution of nitrogen-doped carbon layers and spinel active sites. Innovatively, the composite displays pH-regulated dual-enzyme mimetic activity: under acidic conditions (pH 2.9) it acts as a peroxidase mimic, catalyzing H 2 O 2 -mediated oxidation of dopamine (DA) to dopamine quinone (absorption at 370 nm), while under alkaline conditions (pH 9.0) it exhibits catalase-like behaviour, promoting H 2 O 2 -driven oxidative self-polymerization of DA to polydopamine (absorption at 470 nm). This pH-dependent catalytic switching, attributed to surface charge modulation and differential substrate affinity, enables reliable DA detection across a broad pH range — a key advance over conventional single-pH nanozyme sensors. The sensor demonstrates high sensitivity with detection limits of 0.0179 μM (acidic) and 0.0488 μM (alkaline),and quantification limits of 0.0597 μM (acidic) and 0.163 μM (alkaline), excellent selectivity against common interferents, and good recovery rates (90–103%) in spiked porcine serum samples. The work presents a new strategy for designing smart, environment-adaptive nanozymes from PBA precursors, with promising potential in bioanalysis and point-of-care diagnostics. In this work, the design and synthesis of a novel pH-responsive dual-enzyme nanozyme based on nitrogen-doped carbon-supported CoFe₂O₄ spinel (C(N)@CoFe₂O₄) derived from cobalt-doped Prussian blue analogues (PBAs) has been reported. The work presents a new strategy for designing smart, environment-adaptive nanozymes from PBA precursors, with promising potential in bioanalysis and point-of-care diagnostics. Download: Download high-res image (239KB) Download: Download full-size image