Sustainable agro-waste derived nitrogen-doped carbon dots for sensitive fluorescence detection of ethalfluralin residues in vegetables

Abstract

Ethalfluralin, a critical selective herbicide, necessitates robust and accessible detection methods to safeguard public health and ensure food safety. Current analytical techniques often suffer from complex sample preparation and high operational costs. Addressing this, we report a facile and sustainable approach for synthesizing highly photoluminescent nitrogen-doped carbon dots (N-CDs) derived entirely from agro-waste materials. This novel “green” synthesis leverages hydrothermal treatment of common vegetable biomass (lettuce, cabbage, and spinach) combined with in situ nitrogen doping using urea, significantly enhancing the N-CDs' optical properties. Comprehensive characterization using UV-Vis, FT-IR, fluorescence spectroscopy, XRD, TEM, and CHN analysis confirmed the successful doping and favorable physicochemical attributes of the synthesized N-CDs. Leveraging a Central Composite Design (CCD), we meticulously optimized key sensing parameters (pH, N-CDs concentration, and incubation time) to achieve maximum sensitivity. The developed N-CDs-based fluorescence sensor demonstrates exceptional analytical performance for ethalfluralin detection, exhibiting a broad linear range of 23.3–2012.9 µg kg⁻¹ and a remarkably low limit of detection (LOD) of 18.8 µg kg⁻¹. Importantly, the method exhibits high applicability and provides results in good agreement with the established GC-MS technique when analyzing spiked vegetable samples, validating its accuracy and reliability. This work offers a significant advancement in eco-friendly and cost-effective pesticide residue monitoring, providing a promising alternative to conventional methods.