Lanthanide‐Based Single‐Chain Nanoparticles as “Visual” Pass/Fail Sensors of Maximum Permissible Concentration of Cu²⁺ Ions in Drinking Water

The maximum permissible concentration (m.p.c.) of Cu 2+ ions in drinking water, as set by the World Health Organization (WHO) is m.p.c. (Cu 2+ ) WHO = 30 × 10 −6 m , whereas the US Environmental Protection Agency (EPA) establishes a more restrictive value of m.p.c. (Cu 2+ ) EPA = 20 × 10 −6 m . Herein, for the first time ever, a family of m.p.c. (Cu 2+ ) “visual” pass/fail sensors is developed based on water‐soluble lanthanide‐containing single‐chain nanoparticles (SCNPs) exhibiting an average hydrodynamic diameter less than 10 nm. Both europium (Eu)‐ and terbium (Tb)‐based SCNPs allow excessive Cu 2+ to be readily detected in water, as indicated by the red‐to‐transparent and green‐to‐transparent changes, respectively, under UV light irradiation, occurring at 30 × 10 −6 m Cu 2+ in both cases. Complementary, dysprosium (Dy)‐based SCNPs show a yellow color‐to‐transparent transition under UV light irradiation at ≈15 × 10 −6 m Cu 2+ . Eu‐, Tb‐, and Dy‐containing SCNPs prove to be selective for Cu 2+ ions as they do not respond against other metal ions, such as Fe 2+ , Ag + , Co 2+ , Ba 2+ , Ni 2+ , Hg 2+ , Pb 2+ , Zn 2+ , Fe 3+ , Ca 2+ , Mn 2+ , Mg 2+ , or Cr 3+ . These new m.p.c. (Cu 2+ ) “visual” pass/fail sensors are thoroughly characterized by a combination of techniques, including size exclusion chromatography, dynamic light scattering, inductively coupled plasma‐mass spectrometry, as well as infrared, UV, and fluorescence spectroscopy.