A novel colorimetric method for nitrite detection in food based on histidine-manganese nanozyme with laccase-mimicking activity.

BACKGROUND

Excessive nitrite in food poses a serious threat to public health. This compound not only induces methemoglobinemia by interfering with oxygen transport in the blood but also serves as a precursor to carcinogenic N-nitrosamines, posing long-term cancer risks. Thus, the development of rapid and highly sensitive methods for nitrite detection is crucial for ensuring food safety. Laccase mimics, which have been widely used for the degradation and detection of phenolic compounds, have recently emerged as promising tools for sensing various food contaminants. However, their application for nitrite detection has not been reported to date.

RESULTS

Histidine (His) and manganese (Mn) ion were employed to fabricate a His-Mn nanozyme with laccase-mimicking activity through a simple self-assembly approach. The prepared His-Mn nanozyme exhibits excellent laccase-mimicking catalytic activity and robust stability, enabling the efficient oxidation of various substrates. Specifically, it catalyzes the oxidation of catechol, and the resulting product reacts with nitrite to yield a bright-yellow product with strong absorption at 425 nm. Leveraging this unique chromogenic response, His-Mn nanozyme was employed for the first time to establish a highly selective colorimetric sensing platform for nitrite detection. Notably, the sensing process operates efficiently under neutral and mild conditions (pH 6.5), which is closer to the intrinsic pH of most real samples. The method achieves a low detection limit of 2.87 μM, significantly below the safety limits set by the World Health Organization.

SIGNIFICANCE AND NOVELTY: A novel colorimetric sensing method for nitrite detection was developed by leveraging the laccase-mimicking activity of His-Mn. This method not only expands the diversity of laccase mimics but also provides a new strategy for their application in food safety monitoring.