Although the application of nanozymes has been widely studied, it is still a huge challenge to develop highly active and multifunctional nanozyme catalysts with a wider application prospect. Co 3 O 4 /CoFe 2 O 4 hollow nanocubes (HNCs) with oxygen vacancies were proposed in this study, which had a porous oxide heterostructure with CoFe 2 O 4 as the core and Co 3 O 4 as the shell. The Co 3 O 4 /CoFe 2 O 4 HNCs had three enzyme activities: peroxidase-like, oxidase-like, and catalase-like. Combining XPS depth profiling with density functional theory (DFT), the catalytic mechanism of peroxidase-like activity was explored in depth, which was mainly originated from •OH produced by the synergistic effect between the outer oxygen and inner oxygen and electron transfer between Co and Fe. A colorimetry/smartphone dual sensing platform was designed based on the peroxidase-like activity. Especially, a multifunctional intelligent sensing platform based on deep learning-YOLO v3 algorithm-assisted smartphone was constructed to realize real-time and rapid in situ detection of L-cysteine, norfloxacin, and zearalenone. Surprisingly, the detection limit of norfloxacin was low at 0.015 μM, which was better than that of the newly published detection method in the field of nanozymes. Meanwhile, the detection mechanism of L-cysteine and norfloxacin was successfully investigated by in situ FTIR. In fact, it also showed outstanding applications in detecting L-cysteine in the food environment and norfloxacin in drugs. Furthermore, Co 3 O 4 /CoFe 2 O 4 HNCs also could degrade 99.24% of rhodamine B, along with good reusability even after 10-cycle runs. Therefore, this work provided an in-depth understanding of the synergistic effect between the outer and inner oxygen in the reaction mechanism and an efficient method for establishing a deep-learning-assisted intelligent detection platform. In addition, this research also offered a good guideline for the further development and construction of nanozyme catalysts with multienzyme activities and multifunctional applications.

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A nozzle wall of thickness ≤0.1 mm is applied to decrease the adherence of jet. The stirring device with 20 rotations/min on the upper side of condensed column is used to disperse unsolidified polyethylene glycol pellets. The effect of parameters including vibration frequency f, jet velocity v, and voltage of excitation V on the average diameter d and standard deviation SD% are investigated by response surface methodology and Weber equation. A very good linear regression between d and v/f is presented under optimum V (in this article V = 3.0 V). Both high v and low SD% can also be obtained by optimum V.