Engineering the high-spin 3d orbital in Co3O4 via compressive strain to enhance Immunochromatographic assay

Abstract

Enhancing catalytic activity of peroxidase-like nanozymes is essential for developing ultrasensitive lateral flow immunoassay (LFIA). The peroxidase-like catalytic process involves spin-dependent electron transfer during radical formation, and boosting single electron transfer (SET) efficiency is therefore critical to enhance catalytic performance. Here, we fabricated a strained-Co₃O₄ exhibiting significant atomic compressive strain (ε_xx = −3.34 %, ε_yy = −6.52 %). The atomic-level displacement direction and distance information determined by atomic displacement analysis (ADA) offer detailed information for density functional theory computational modeling. We discovered that the strain engineering elevated crystal field splitting energy, which promotes the transition of Co₃O₄ from low-spin states (t_2g⁶e_g⁰) to high-spin states (t_2g⁴e_g²), resulting in efficient SET performance. Spin-state modulation dramatically enhances the peroxidase-like catalytic efficiency, resulting in 28.0-fold and 11.8-fold lower Michaelis constants (K_m) for TMB and H₂O₂, respectively, than those of the pristine-Co₃O₄. In addition, the strained-Co₃O₄ was successfully employed in the development of LFIA for Xanthomonas oryzae pv. oryzae (Xoo) monitoring, and the LFIA achieved a detection sensitivity of 5 × 10² CFU mL⁻¹ that was 20-fold higher than Au nanoparticles-based LFIA and was 2–3 orders of magnitude higher than commercial LFIAs. Our findings established a correlation between strain–spin orbit–peroxidase-like activity, offering a promising strategy for the rational design of nanozymes.