Multifunctional Probe Based on CTAB-Cu Nanoparticles for Fluorescence and Colorimetric Dual-Read-Out Determination of p‑Nitrophenol and Glyphosate

The quantitative analysis of glyphosate has significant implications for the evaluation of food quality and environmental safety risks. First, copper nanoparticles (Cu NPs) were synthesized using cetyltrimethylammonium bromide (CTAB) as a stabilizing agent, which resolved the limitation associated with atmospheric oxidation of Cu NPs and provided excellent fluorescence stability. Interestingly, the fluorescence of blue-emitting CTAB-Cu NPs was quenched by pH-responsive p-nitrophenol (p-NP) via Förster resonance energy transfer. Herein, a dual read-out sensor based on CTAB-Cu NPs and p-NP was constructed for glyphosate detection. Specifically, acetic acid (HAc) from acetylcholine (ACh) via hydrolysis catalyzed by acetyl cholinesterase (AChE) reduced the pH of the mixed solution and prevented the loss of protons from p-NP, which allowed the fluorescence emission by CTAB-Cu NPs. The presence of glyphosate inhibited the activity of AChE, and the increased pH resulted in proton loss. The fluorescence intensity of CTAB-Cu NPs was quenched, and the solution color changed from colorless to yellow with a UV absorption peak at 400 nm. The sensor can detect ultra-trace levels of glyphosate residues with a limit of detection of 5.43 ng/L. The obtained biosensor was successfully utilized to monitor the degradation of glyphosate in the roots of cabbage and cultivated soil.