Rapid and ultrasensitive colorimetric detection of Cd ²⁺ ions in water using gold nanoparticles derived from Acacia mangium

Rapid and ultrasensitive monitoring of Cd2+ in aquatic environments remains a critical challenge due to its high toxicity and persistence. This work develops a green, ligand-free colorimetric sensing platform using phytochemical-capped gold nanoparticles synthesized from Acacia mangium leaf extract (AuNPs-Am). The plant-derived polyphenolic compounds act simultaneously as reducing and surface-coordinating agents, enabling one-step nanoparticle synthesis while introducing abundant oxygen-donor binding sites. Upon Cd2+ exposure, coordination interactions at the AuNPs-Am interface induce nanoparticle aggregation, leading to localized surface plasmon resonance modulation and a visible color change. Quantitative analysis based on the absorbance difference (A530–A564) exhibits a linear range of 8.896–889.6 µM (R2 = 0.9953) with detection and quantification limits of 0.09 and 0.30 µM, respectively. The sensor shows strong selectivity against competing metal ions and reliable performance in real water samples with recoveries of 91.40–110.48%. This approach demonstrates a rapid, cost-effective, and environmentally benign strategy for Cd2+ detection.