Self-synergy-powered Ni/Fe nanocube-based cholesterol detection with dual modes

Nanoenzyme-leveraged multimode detection would benefit enhancing sensitivity and mitigating detection error. Moreover, multienzyme-like nanozymes hold tremendous potential in sensing by offering synergistic effects and cascaded catalysis. Herein, cost-effective multienzymic Ni/Fe nanocubes (Ni/FeNCs) were synthesized via a facile co-precipitation, and verified to catalyze H₂O₂ decomposition as peroxidase (POD) and catalase (CAT) mimics. Thereby, a dual-mode sensing platform based on Ni/FeNC and cholesterol oxidase (ChOx) was developed for cholesterol detection. Utilizing the H₂O₂ produced via the oxidation of cholesterol catalyzed by ChOx, OH^•/O₂^•- radicals and O₂ were formed efficiently via Ni/FeNCs-based H₂O₂ decomposition, facilitating the generation of chemiluminescence (CL) and fluorescence signals. For CL assay, an Ni/FeNC-luminol-H₂O₂ CL system was fabricated, where both POD-mimic-mediated radical decomposition of H₂O₂ and ferricyanide ions in Ni/FeNCs could induce CL reaction with respective mechanism. Notably, these two CL processes were both deduced to be enhanced by in-situ generated O₂. This dual-catalyzed luminol CL system, involving self-cascade catalysis of ferricyanogen and CAT mimic as well as the self-synergy between POD-like and CAT-like activities of Ni/FeNCs, was proposed for the first time, and able to boost CL signal. To generate fluorescent signal, o-phenylenediamine was introduced, and oxidized by both OH^•/O₂^•- and O₂ produced via POD/CAT-mimic-mediated H₂O₂ decomposition to 2,3-diaminophenazinc, which could quench the fluorescence of WS₂ quantum dots via internal filtration effect. The Ni/FeNC-based dual-mode assay is applicable and flexible for cholesterol detection. Particularly, the low-cost Ni/FeNC is a promising candidate of luminol-H₂O₂ CL system due to its dual-CL-mechanism involving self-cascade and synergistic catalysis.