Although nanozymes proved a promising utility in sensing applications, they often lack a rational approach in their design. Herein, magnetite chitosan hydrogel (MCH) is reported as a rational peroxidase nanozyme for the smartphone-assisted colorimetric detection of thiabendazole (TBZ). Chitosan due to its polycationic nature, renders a microenvironment similar to amino acids in HRP enzyme. Characterizations of the nanozyme using SEM, XRD, and XPS confirmed the distribution of Fe₃O₄NPs on the chitosan matrix. The peroxidase activity was demonstrated using TMB and H₂O₂ as substrates which resulted in a characteristic absorption at 652 nm. MCH nanozyme showed a 24% higher peroxidase activity in acidic pH than the pristine Fe₃O₄ confirming the role of chitosan in boosting the electron transfer. Kinetics result suggested the catalytic reaction followed a Michalis-Menten model with K_m and V_max of 0.45 mM and 15 μM/min for TMB and 2.8 mM and 4.18 μM/min for H₂O₂ respectively_. These values are competitive with natural HRP enzymes reported before. Further, MCH nanozyme showed improved thermal and temporal stability as well as reusability retaining 80% of its activity after the 4th cycle. TBZ showed concentration-dependent inhibition on the peroxidase activity. The degree of inhibition exhibited a linear relationship with the concentration of TBZ from 0.1 to 100 μM (R² = 0.998) enabling the detection of TBZ down to 0.73 and 1.84 μM in a spectrometer and smartphone-based readouts respectively. The results show the potential of the prepared nanozyme as a point-of-need sensor for food safety monitoring.

尽管纳米酶在传感应用中被证明具有广阔的应用前景，但它们在设计中往往缺乏合理的方法。在此，磁铁矿壳聚糖水凝胶（MCH）被报道为一种合理的过氧化物酶纳米酶，用于智能手机辅助比色检测噻菌灵（TBZ）。壳聚糖由于其聚阳离子性质，可提供类似于 HRP 酶中氨基酸的微环境。_{使用 SEM、XRD 和 XPS 对纳米酶进行表征，证实了 Fe 3} O ₄纳米颗粒在壳聚糖基质上的分布。_{使用 TMB 和 H 2} O ₂作为底物证明了过氧化物酶活性，导致 652 nm 处的特征吸收。_{MCH 纳米酶在酸性 pH 条件下表现出比原始 Fe 3} O ₄高 24% 的过氧化物酶活性，证实了壳聚糖在促进电子转移方面的作用。动力学结果表明催化反应遵循Michalis-Menten模型，TMB的K _m和V _{max分别为0.45 mM和15 μM/min，H 2} O ₂的K m 和V max 分别为2.8 mM和4.18 μM/min _。这些值与之前报道的天然 HRP 酶具有竞争力。此外，MCH 纳米酶表现出改善的热稳定性和时间稳定性以及可重复使用性，在第四次循环后仍保留 80% 的活性。TBZ 对过氧化物酶活性表现出浓度依赖性抑制。抑制程度与 TBZ 浓度在 0.1 至 100 μM 范围内呈线性关系 (R ²  = 0.998)，从而能够在光谱仪和基于智能手机的读数中分别检测低至 0.73 和 1.84 μM 的 TBZ。结果表明所制备的纳米酶作为食品安全监测的需求点传感器的潜力。