Nanozyme based on ZIF-8 for the colorimetric detection of sulfonamides in cow milk

A simple and time-saving colorimetric method was developed to quantify sulfonamides (SAAs) in milk via inhibition of the human carbonic anhydrase II (hCAII)-like activity of ZIF-8 that can hydrolyze p -nitrophenyl acetate ( p NPA) to p -nitrophenol ( p NP), following the color change from yellow to colorless. Effects of different reaction conditions, including pH, temperature, amount of ZIF-8, and incubation time , were investigated. The value of Michaelis-Menten constant ( K m ) is measured to be 0.15 mM, which exhibits high affinity to p NPA. The IC 50 (0.17, 0.24, and 0.60 mM) and inhibition constant ( K i ) (0.09, 0.13, and 0.33 mM) of sulfamethazine (SD), sulfadimethoxine (SDM), and sulfathiazole (ST) on ZIF-8 were measured, respectively. Moreover, the activity of ZIF-8 remains more than 90.0% of its initial activity after 30 days’ storage. The colorimetric method for SD, SDM, and ST determination was established at the linear ranges of 6.3–750.0 μM (1.75–208.75 mg/kg), 6.3–750.0 μM (1.96–232.75 mg/kg), and 5.0–1250.0 μM (1.28–319.15 mg/kg) with limit of detection of 4.3, 3.2, and 3.9 μΜ (1.2, 0.99, and 0.96 mg/kg), respectively. In addition, the spiked recoveries of SAAs in milk sample are in the range of 81.6%–106.7% with RSD less than 6.5%. In short, the developed colorimetric method can achieve rapid analysis of SAAs in milk with simple operations.