A novel ratiometric colorimetric sensor based on two-dimensional cobalt-based nanoenzyme (D-ZIF-67) was developed for sensitive detection of nitrite. D-ZIF-67 was synthesized using a one-step precipitation method,and its structure and morphology were characterized using scanning electron microscopy and transmission electron microscopy. D-ZIF-67 catalyzed the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue oxidation product (oxTMB) with a distinct absorption peak at 652 nm. In the presence of nitrite,oxTMB underwent further oxidation and diazotization,resulting in a decrease in the absorbance at 652 nm (A652) and an increase in the absorbance at 450 nm (A450) due to the formation of a yellow product. Based on the linear relationship between logarithm of nitrite concentration and the ratio signal A652/450,sensitive detection of nitrite was achieved. Under the optimal conditions,the detection range of nitrite was found to be 3−300μmol/L,with a detection limit (S/N=3) of 0.08μmol/L. Compared to traditional single-signal methods,the ratiometric colorimetric mode exhibited better interference resistance. The method was applied to detection of nitrite in sausages and salted duck eggs,yielding recoveries of 97.7％−104.1％.
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