A Turn-On Fluorescence Method Based on Silver Nanoparticles for 2,4,5-Trichlorophenoxyacetic Acid Determination in Environmental Waters.

2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) is a chlorophenoxy herbicide of environmental concern due to its persistence, toxicity, and potential ecological and human health risks. The development of rapid, sensitive, and environmentally friendly analytical methods for its determination remains an important challenge. The novelty of this work lies in the use of a hexadecyltrimethylammonium bromide (HTAB)-stabilized silver nanoparticle (AgNP) fluorescence system as a simple analytical platform for the determination of 2,4,5-T in environmental water samples, combining minimal sample treatment with satisfactory analytical performance. The synthesized nanoparticles were characterized by scanning electron microscopy (SEM), dynamic light scattering (DLS), UV-Vis absorption spectroscopy, and fluorescence spectroscopy. Experimental variables affecting the analytical response were systematically optimized, and the method was evaluated in environmental and tap water samples. Under the optimized experimental conditions, the addition of 2,4,5-T to the AgNPs-HTAB system produced a reproducible increase in fluorescence intensity at 365 nm using an excitation wavelength of 300 nm. The complete calibration dataset showed excellent linearity, with the regression equation S = 0.5000 C + 9.9906 (R² = 1.0000), where S is the fluorescence signal (a.u.) and C is the 2,4,5-T concentration (µg L⁻¹). Based on 16 independent blank measurements (σ = 0.12 a.u.), the limit of detection (LOD) and limit of quantification (LOQ) were 0.79 and 2.40 µg L⁻¹, respectively, and the quantitative working range was established as 2.40-1600 µg L⁻¹. The method showed satisfactory precision and accuracy, with recoveries close to 100% in fortified water samples. SEM analysis revealed a mean nanoparticle diameter of 90.5 ± 0.89 nm, while DLS measurements showed a particle population centered at approximately 97 nm. The greenness of the analytical procedure was assessed using the AGREE metric, yielding a score of 0.78, while the Nanomaterials Assessment Tool (NAT) yielded a score of 71/100 for the AgNPs-HTAB system. Overall, the proposed AgNPs-HTAB fluorescence method provides a simple, sensitive, and comparatively low-sample-treatment approach for the determination of 2,4,5-T in environmental waters.