Monodispersed colloidal gold nanoparticles (AuNPs) were synthesized by an easy, cost-effective, and eco-friendly method. The AuNPs were mostly quasi-hexagonal in shape with sizes ranging from 15 to 18 nm. A screen-printed electrode modified with AuNPs (AuNPs/SPE) was used as an electrochemical sensor for the detection of As( III ) in water samples. The mechanistic details for the detection of As( III ) were investigated and an electrochemical reaction mechanism was proposed. Under the optimal experimental conditions, the sensor was highly sensitive to As( III ), with a limit of detection of 0.11 μg L ~(?1) (1.51 nM), which is well below the regulatory limit of 10 μg L ~(?1) established by the United States Environmental Protection Agency and the World Health Organization. The sensor responses were highly stable, reproducible, and linear over the As( III ) concentration range of 0.075 to 30 μg L ~(?1) . The presence of co-existing heavy metal cations such as lead, copper, and mercury did not interfere with the sensor response to As( III ). Furthermore, the voltammogram peaks for As( III ), lead, copper, and mercury were sufficiently separate for their potential simultaneous measurement, and at very harsh acidic pH it may be possible to detect As( V ). The AuNPs/SPE could detect As( III ) in tap water samples at near-neutral pH, presenting potential possibilities for real-time, practical applications.
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