Luminol

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.

Nitrogen doping enhances the catalytic performance of carbon-based metal-free electrocatalysts (C-MFECs) by modifying their chemical environment. Understanding the structure-catalytic activity relationship of nitrogen-doped (N-doped) C-MFECs is crucial for elucidating catalytic mechanisms and designing efficient electrocatalysts, but it remains challenging. Recently, reactive oxygen species (ROS)-triggered electrochemiluminescence (ECL) has shown great potential for uncovering these mechanisms due to its simple setup, low background signal, wide dynamic range, and high sensitivity. In this study, four types of N-doped C-MFECs with varying nitrogen dopant types (denoted as N-C_x, where x represents the annealing temperature) towards the electrochemical reduction of H₂O₂ are evaluated by monitoring the cathodic ECL of the luminol-H₂O₂ system in the low negative-potential region. Among these, N-C₉₀₀, contains a higher content of graphitic nitrogen exhibits superior catalytic performance in activating H₂O₂ to generate significant amounts of ROS, as evidenced by its markedly enhanced ECL emission. The increased incorporation of graphitic nitrogen into the carbon plane likely improved H₂O₂ adsorption and its capacity to generate ROS. A sensitive antioxidant-mediated ECL platform was successfully developed for detecting antioxidant levels in orange juice, demonstrating potential for evaluating antioxidant capacity. This study not only provides insights into the catalytic mechanisms of N-doped C-MFECs but also highlights the potential of ECL as a versatile tool for studying and designing electrocatalysts.