Lanthanide-Based Single-Chain Nanoparticles as "Visual" Pass/Fail Sensors of Maximum Permissible Concentration of...

The maximum permissible concentration (m.p.c.) of Cu²⁺ ions in drinking water, as set by the World Health Organization (WHO) is m.p.c. (Cu²⁺)_WHO = 30 × 10^-6 m, whereas the US Environmental Protection Agency (EPA) establishes a more restrictive value of m.p.c. (Cu²⁺)_EPA = 20 × 10^-6 m. Herein, for the first time ever, a family of m.p.c. (Cu²⁺) "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 Cu²⁺ 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 Cu²⁺ in both cases. Complementary, dysprosium (Dy)-based SCNPs show a yellow color-to-transparent transition under UV light irradiation at ≈15 × 10^-6 m Cu²⁺. Eu-, Tb-, and Dy-containing SCNPs prove to be selective for Cu²⁺ ions as they do not respond against other metal ions, such as Fe²⁺, Ag⁺, Co²⁺, Ba²⁺, Ni²⁺, Hg²⁺, Pb²⁺, Zn²⁺, Fe³⁺, Ca²⁺, Mn²⁺, Mg²⁺, or Cr³⁺. These new m.p.c. (Cu²⁺) "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.