NPA-Cu²⁺ Complex as a Fluorescent Sensing Platform for the Selective and Sensitive Detection of Glyphosate

Glyphosate is a highly effective, low-toxicity, broad-spectrum herbicide, which is extensively used in global agriculture to control weeds and vegetation. However, glyphosate has become a potential threat to human and ecosystem because of its excessive usage and its bio-concentration in soil and water. Herein, a novel turn-on fluorescent probe, N-n-butyl-4-(3-pyridin)ylmethylidenehydrazine-1,8-naphthalimide (NPA), is proposed. It efficiently detected Cu²⁺ within the limit of detection (LOD) of 0.21 μM and displayed a dramatic turn-off fluorescence response in CH₃CN. NPA-Cu complex was employed to selectively and sensitively monitor glyphosate concentrations in real samples accompanied by a fluorescence turn-on mode. A good linear relationship between NPA and Cu²⁺ of glyphosate was found in the range of 10-100 μM with an LOD of 1.87 μM. Glyphosate exhibited a stronger chelation with Cu²⁺ than NPA and the system released free NPA through competitive coordination. The proposed method demonstrates great potential in quantitatively detecting glyphosate in tap water, local water from Songhua River, soil, rice, millet, maize, soybean, mung bean, and milk with mild conditions, and is a simple procedure with obvious consequences and no need for large instruments or pretreatment.