Detection of Cu(II) in water by using N, S co-doped carbon dots

Determination of Cu(II) ions in surface and drinking water is a high-priority issue both for the environment and human health. Here, we report on the preparation via a hydrothermal method of stable water suspensions of N and S co-doped carbon dots. This material demonstrated selective sensitivity to the presence of copper in water with the appearance of a characteristic absorption band at 658 nm resulting in a visual color variation from orange to dark brown. The colorimetric measurement, carried out by recording the difference between the absorbance at two wavelengths, showed a good linear dependence on the ion concentration from 1 to 100 μM with a lower limit of detection of 300 nM, significantly below the values set by health and environmental organizations. The sensing method is simply based on the addition of the contaminated sample to the carbon dot solution without any other reagents or previous treatment. Moreover, the sensing solution showed stability for at least 6 months after preparation.