A novel AgNPs-based colorimetric sensor for rapid detection of Cu2+ or Mn2+via pH control

Abstract

In this study, we propose a new silver nanoparticles (AgNPs)-based colorimetric sensor for rapid detection of Cu²⁺ or Mn²⁺ at pH 1.9 or 12.0, respectively. At pH 1.9, the AgNPs stabilized with sodium pyrophosphate (Na₄P₂O₇) and hydroxypropylmethylcellulose (HPMC) gradually become smaller in the presence of Cu²⁺ resulting in a color change of the solution from yellow to colorless. At pH 12.0, however, the AgNPs aggregate immediately in the presence of Mn²⁺, which induces a color change of the solution from yellow to brown. The incubation time between the detection system and metal ion (Cu²⁺ or Mn²⁺) is fixed at 10 min. This mechanism is confirmed using UV-vis spectroscopy, Transmission electron microscopy (TEM), Dynamic light scattering (DLS) and Fourier-Transform Infrared Spectrometry (FT-IR). At the optimized experimental conditions, the selectivity of our AgNPs-based detection system is excellent for Cu²⁺ or Mn²⁺ compared with other metal ions. The limit of detections (LODs) of Cu²⁺ and Mn²⁺ by the naked eye are respectively 0.05 and 0.5 μM, and those by UV-vis spectroscopy are respectively 2.0 and 20 nM. The above LODs are all lower than the corresponding national drinking water standards (16 μM of Cu²⁺ and 1.8 μM of Mn²⁺). The applicability of our AgNPs-based colorimetric sensor is also validated by detection of Cu²⁺ and Mn²⁺ in tap water and lake water. Therefore, these results reinforce that our AgNPs-based colorimetric sensor is applicable to rapid colorimetric detection of Cu²⁺ and Mn²⁺ in complicated real water samples with excellent selectivity and high sensitivity.