Chitin-Functionalized Carbon Nanofiber-Based Electrochemical Sensor for Rapid and Sensitive Detection of 4-Methylaminophenol in Aquatic Ecosystems

4-Methylaminophenol (4-MAP), commonly used in hair dye and photography industries, has a major undesirable ecological effect owing to its toxicity, persistence, and bioaccumulation in aquatic environments. Even at low concentrations, 4-MAP poses a threat to aquatic life and human health, and therefore accurate detection is essential as an environmental indicator. Nevertheless, the current approaches are either insensitive enough or too complicated to be applied regularly. In this work, we fabricated a chitin-functionalized carbon nanofiber composite (chitin/f-CNF) using ultrasonication technique and characterized using XRD, FT-IR, Raman, FE-SEM, EDX, elemental mapping, and HR-TEM analyses. The composite was applied to modify a glassy carbon electrode (GCE) and employed in the electrochemical detection of 4-MAP using cyclic voltammetry and differential pulse voltammetry. The chitin/f-CNF modified GCE demonstrates improved electron transfer and electrocatalytic activity compared to other modified and unmodified electrodes. The developed sensor achieved high sensitivity (1.867 μA μM^-1 cm^-2), a wide linear range (0.01-747.19 μM), a low detection limit (4.2 nM), and a low quantification limit (14.15 nM). Computational density functional theory simulations further elucidated the electronic energy landscape and charge-transport pathways of 4-MAP during the electrochemical process. The sensor also exhibited excellent selectivity in the presence of potential interfering substances, along with remarkable reproducibility, stability, and repeatability. Real water samples display high recoveries with an accuracy of 97.93% (tap), 99.03% (pond), and 98.93% (river). Overall, the proposed chitin/f-CNF modified GCE demonstrates a simple, inexpensive, and reliable sensitive analysis of 4-MAP which will improve environmental pollution and water quality management.