Sensitive Detection of Copper(II) Ions in Water Using Nitrogen-Doped Carbon Quantum Dots Synthesized from Pine Cone Lignin and Lysine

Abstract

The accurate and rapid determination of trace copper Cu(II) ions in environmental water is of great significance for both ecological safety and human health. In this work, a novel, eco-friendly, and highly sensitive fluorescence sensor was developed using carbon dots synthesized from pine cone deep eutectic solvent (DES) lignin and doped with lysine for the selective detection of Cu(II) ions. The synthesized carbon dots exhibited excellent optical properties. They demonstrated a strong, concentration-dependent fluorescence response to Cu(II) with a wide linear range of 2.81 & times; 10-7-5.87 & times; 10-5 and a remarkably low limit of detection (LOD) of 2.8 & times; 10-8 mol L-1. To validate the practical applicability and reliability of the proposed sensor, it was successfully employed for Cu(II) determination in highly complex matrices, including various certified reference materials (primary drinking water, NASS-5 seawater, SM-WW1, and SM-WW2 wastewater) and real environmental samples (ground, lake, and tap water). The standard addition method yielded excellent recovery rates ranging from 98.9 to 104.4%, with relative standard deviations (RSDs) strictly below 4.3%. Furthermore, the analytical results were statistically compared with the standard flame atomic absorption spectrometry (FAAS) method at a 95% confidence level, showing exceptional agreement and no significant differences. The proposed lysine-doped carbon dot sensor offers a highly accurate, cost-effective, and highly selective alternative for the routine monitoring of Cu(II) in diverse and complex environmental water samples, effectively overcoming significant matrix interference.