The use of water-soluble luminescent CdSe quantum dots (QDs), whose surface was modified either with 2-mercaptoethane sulphonic acid or with 2-mercaptoacetic acid, was investigated for the sensitive and selective determination of copper(II) ions in aqueous solutions. A pH 5.5 was selected for measurement. Also, the effect of the presence of different surfactant agents in the sample solution, in order to stabilize the fluorescent signals of the QDs in water, has been investigated. A 10 −3 M of dodecyltrimethylammonium chloride final concentration was selected. Fluorescence signals were found to be stable for at least several days in such conditions. Higher sensitivity was obtained for the sulphonic-modified CdSe QDs. Detection limits for Cu(II) of 0.2 μg l −1, a dynamic range up to 30 μg l −1, and a R.S.D. of ±2.8% for 10 replicates of a 2.5 μg l −1 Cu(II) solution were obtained as analytical performance characteristics. Besides, the influence on the fluorescence signal of foreign cations, including Na +, K +, Ca 2+, Mg 2+, Zn 2+, Mn 2+, Co 3+, Ag +, Hg 2+ and Fe 3+ was studied (to avoid inner filter effect, the colourless complex FeF 6 3− was investigated instead of Fe 3+). Results showed a high selectivity of the sulphonic-modified QDs towards Cu(II) ions. The proposed method demonstrated improved sensitivity and selectivity characteristics for Cu(II) determinations as compared to other already described luminescence QDs-based analytical methods for metal ions determinations. Analytical applicability of the QDs has been demonstrated by tap and fountain water analysis. Results of Cu(II) determinations were in good agreement to those obtained by using an alternative analytical method.