Síntese, caracterização e aplicação de diferentes carbon dots como nanossensores fluorescentes na detecção de glifosato

Abstract

Glyphosate, one of the most widely used herbicides worldwide, poses potential risks to human health and the environment, mainly due to its excessive use, persistence in soil, and high solubility. Its detection by conventional methods, such as HPLC and GC, presents several drawbacks, including high instrumentation costs and complex procedures. Carbon dots (CDs), fluorescent carbon-based nanomaterials with sizes below 10 nm, have emerged as a promising alternative for sensing applications due to their simple synthesis, low toxicity, and photoluminescent properties. CD-based sensors enable rapid analysis and have been applied to glyphosate detection through fluorescence quenching or enhancement, offering a simple and cost-effective sensing approach. In this study, a fast and straightforward methodology was developed for the detection of glyphosate in water using carbon dots (CDs) synthesized via hydrothermal carbonization from different carbon precursors. Four types of CDs were synthesized using distinct organic acids: L-ascorbic acid (CAA), citric acid (CCA), maleic acid (CMA), and succinic acid (CSA), as carbon sources, while ammonium citrate was used as the nitrogen precursor in all cases. The synthesized CDs exhibited blue fluorescence, with quantum yields of 9.3%, 12.0%, 21.5%, and 21.6% for CAA, CMA, CSA, and CCA, respectively. Infrared spectroscopy was used to characterize the surface functional groups of the CDs, revealing a predominance of carboxylic groups in their structures. TEM images showed non-aggregated, spherical particles with average sizes ranging from 1.7 to 2.8 nm. The sensors were based on CDs that exhibit strong interactions with Fe3+ ions, initially leading to significant fluorescence quenching, followed by fluorescence recovery upon the addition of glyphosate. This enabled the indirect detection of the herbicide. The limits of detection for glyphosate in water were 1.57 μM (CAA), 4.64 μM (CCA), 11.16 μM (CMA), and 0.59 μM (CSA). The results obtained from testing the nanosensor with a real tap water sample confirmed that the proposed fluorescent sensor is a promising tool for glyphosate detection in aqueous matrices, demonstrating both sensitivity and potential for application under real-world conditions.