Engineered Co₃O₄ nanoboxes boost luminol chemiluminescence for selective Mn²⁺ sensing

Chemiluminescence (CL) is a powerful analytical tool that has gained increasing interest in various fields due to its rapid response, simplicity, cost-effectiveness, and higher sensitivity compared to traditional complex methods for detecting trace toxic metals. The traditional luminol/H₂O₂ CL method suffers from low emission efficiency. As a result, the synthesis of nanozymes as co-reaction accelerators has attracted increasing attention to improve CL sensitivity. Spinel-type oxides have been used in many fields because of their cost-effectiveness, excellent catalytic performance, and eco-friendliness; however, they have seldom been used in CL. Herein, a simple chemical etching method of a self-templating ZIF-67 nanocube MOF precursor using tannic acid, followed by thermal annealing, was employed to synthesize Co₃O₄ nanoboxes (NBs). The Co₃O₄ NBs showed peroxidase-like activity and boosted the luminol/H₂O₂ CL by a factor of 670. The improved catalytic efficiency is attributed to increased H₂O₂ adsorption on the confined surfaces of Co₃O₄ NBs, generating more reactive oxygen species radicals and significantly enhanced luminol/H₂O₂ CL signals. Moreover, Mn²⁺ remarkably quenched CL, enabling highly sensitive Mn²⁺ detection with a wide linear range from 50 nM to 5 µM and a limit of detection as low as 2.5 nM.