Fe-Single-Atom Nanozyme Catalysts for Sensitive and Selective Detection of Nitrite via Colorimetry and Test Strips

Here, a sensitive and selective strategy for the detection of nitrite via colorimetry and test strips was developed based on Fe-single-atom catalysts (Fe SACs) through the oxidation–reduction and diazotization reactions. Fe SACs possess excellent oxidase-like (OXD) catalytic activity, which can catalyze the oxidation of the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue TMBox with the appearance of an obvious absorbance peak at 652 nm in the presence of oxygen. With the addition of nitrite (NO2–), the oxidation–reduction and diazotization reactions between TMB/TMBox and nitrite can induce the color of the solution to change from blue to green and finally to yellow, with the increase of the peak at 445 nm. Based on this strategy, a dual-signal-ratio colorimetric detection method for nitrite was proposed. Within the concentration range of 1–120 μM, the ratio of A652/A445 has a favorable linear relationship with the logarithm concentration of NO2–, with a detection limit of 0.238 μM. By combining smartphones with the colorimetric method, a more intuitive, visual, and convenient test strip detection platform was developed, which can be utilized for the detection of nitrite within 2–200 μM. The analysis strategy based on the Fe-single-atom nanozyme catalysis integrated with the specific redox/diazotization reaction not only provides a dual-signal ratio sensing with good sensitivity but holds the advantage of good selectivity for the utilization of the specific chemical reaction, which has broad application prospects in food safety supervision and food screening.