·ATP-enhanced PB@MIL-100(Fe) nanozyme enables dual-mode ratiometric colorimetric and smartphone-based hydrogel detection of nitrite in food samples.

BACKGROUND

Nitrite residues pose significant threats to food safety, as excessive consumption of this may cause serious health risks to human. Conventional techniques such as Griess reagent and chromatographic methods can successfully quantify nitrite levels, but these approaches often suffer from complex sample preparation, poor selectivity, expensive instrumentation, necessitate professional operators and time-consuming procedures. These limitations restrict their practical application for detection nitrites in point-of-care testing (POCT). Therefore, developing sensitive and portable nitrite detection methods remains critically important for food safety monitoring.

RESULTS

Herein, we developed a novel dual-mode sensing platform based on composite nanozymes PB@MIL-100(Fe)@ATP for sensitive, selective and portable nitrite detection. This platform integrates Prussian Blue with MIL-100(Fe) metal-organic framework and exploits adenosine triphosphate (ATP) as an enhancer. The resulting PB@MIL-100(Fe)@ATP demonstrated excellent peroxidase-like (POD-like) catalytic activity, which catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to form blue-colored oxidized TMB (TMBox) with a characteristic absorption peak at 652 nm. In the presence of nitrites, TMBox specifically undergoes diazotization under acidic conditions to produce yellow diazotized TMB, exhibiting increased absorbance at 450 nm while decreasing at 652 nm. The ratiometric colorimetric assay achieved a detection limit of 0.17 μM within 20 min through absorbance ratio analysis at 652/450 nm. Furthermore, a smartphone-assisted hydrogel sensing method with detection limit of 1.68 μM was developed for point-of-care nitrites monitoring through image capture and color analysis, providing equipment-free operation.

SIGNIFICANCE: The ATP-enhanced PB@MIL-100(Fe) nanozyme was successfully applied to detect nitrites with high recovery rates in real pickled vegetables, sauerkraut, and sausage samples. This dual-mode platform demonstrated excellent selectivity, high quantitative accuracy, and practical applicability in complex food matrices, providing a simple, rapid and versatile tool for on-site food safety monitoring.