Detection of dithiocarbamate pesticide residues in tea by colorimetric and fluorescent double-mode probe regulated by tyrosinase

Abstract

In this study, a colorimetric/fluorescent double-mode probe for sensitive detection of dithiocarbamates (DTCs) pesticides residues was constructed based on the fluorescence controllable property of Mn³⁺-sealed metal-organic framework (MnMOF), the chromogenic reaction of enzyme reaction products, and inhibition of tyrosinase activity by DTCs. DTCs inhibited the activity of tyrosinase and impeded the consumption of catechol (CC), thereby weakening the colorimetric signal. The redox reaction between residual CC and MnMOF led to backbone collapse and release of free porphyrin (TCPP), which caused fluorescence enhancement of the probe solution. As the concentration of DTCs increased, the color of probe solution gradually transitioned from reddish brown to light pink in daylight, and the red fluorescence was gradually enhanced under 365 nm UV light. Under the optimal conditions and using zineb as a representative of DTCs, the probe achieved the sensitive response to zineb over the concentration range of 0.03 ∼ 1.1 μg mL⁻¹. The detection limits were 9.23 ng mL⁻¹ and 5.95 ng mL⁻¹ in colorimetric and fluorescent modes, respectively. The practical applicability of the probe was demonstrated by the detection of zineb residues in tea. In this study, a simple, sensitive, and reliable double-mode analysis platform was established for the identification of DTCs residues in tea, which is of great significance for ensuring the quality and safety of tea and human health.