A Turn-On Fluorescent Assay for Glyphosate Determination Based on Polydopamine-Polyethyleneimine Copolymer via the Inner Filter Effect

Abstract

The threat of glyphosate to food safety has attracted widespread attention. Consequently, it is highly urgent to develop a sensitive and accurate method for glyphosate detection. Herein, a turn-on fluorescent method for glyphosate detection using polydopamine-polyethyleneimine (PDA-PEI) copolymer as a fluorescent probe and p-nitrophenylphosphate (PNPP)/alkaline phosphatase (ALP) as a fluorescence quenching system is developed. The PDA-PEI copolymer was prepared by a one-pot method under mild condition, and its fluorescence kept almost unchanged after storing in a refrigerator for one month. ALP catalyzed the hydrolysis of PNPP to p-nitrophenol (PNP) that caused the fluorescence quenching of PDA-PEI copolymer via the inner filter effect. However, glyphosate inhibited ALP activity, thereby preventing the formation of PNP and restoring the fluorescence signal. Under the optimized conditions, the fluorescence of PDA-PEI copolymer depended on glyphosate concentrations ranging from 0.2 to 10 μg/mL with a detection limit of 0.06 μg/mL. Moreover, this assay was applied to detect glyphosate in real samples using the standard addition method. The recoveries were in the range from 88.8% to 107.0% with RSD less than 7.78%. This study provides a novel insight for glyphosate detection and expands the applications of fluorescent copolymer.