Highly selective fluorescent sensor for ammonium ions

Abstract

Ammonium ions (NH₄⁺) are one of the important metabolic products and are closely related to human health. Currently, many NH₄⁺ detection methods are inevitably disturbed by amino acids, K⁺, or other substituted amines (such as trimethylamine). To alleviate this problem, a new sensor was designed in this study, which consisted of the fluorescent indicator KS, hydrogel medium D4, and a hydrophobic membrane. In this sensing system, NH₄⁺ and NH₃ coexisted in equilibrium; NH₃ could pass through a suitable hydrophobic film and transform into NH₄⁺, which complexed with KS, resulting in a change of the probe's fluorescence intensity. By adjusting the internal composition of the sensing matrix, an excellent NH₄⁺ sensor NS-1 was obtained; it demonstrated effective detection of NH₄⁺ in the range 0.3–15.6 mM with a limit of detection (LOD) of 258 μM, and it was not disturbed by K⁺ or other substituting amines.