Novel Amino-pillar[5]arene as a Fluorescent Probe for Highly Selective Detection of Au³⁺ Ions

A novel fluorescent probe, amino-pillar[5]arene (APA), was prepared via a green, effective, and convenient synthetic method, which was characterized by nuclear magnetic resonance (NMR), infrared (IR), and high-resolution mass spectrometry. The fluorescence sensing behavior of the APA probe toward 22 metal ions in aqueous solutions were studied by fluorescence spectroscopy. The results showed that APA could be used as a selective fluorescent probe for the specificity detection of Au³⁺ ions. Moreover, the detection characteristics were investigated by fluorescence spectral titration, pH effect, fluorescence competitive experiments, Job's plot analysis, ¹H NMR, and IR. The results indicated that detection of Au³⁺ ions by the APA probe could be achieved in the range of pH 1-13.5 and that other coexisting metal ions did not cause any marked interference. The titration analysis results indicated that the fluorescence intensity decreased as the concentration of Au³⁺ ions increased, with an excellent correlation (R ² = 0.9942). The detection limit was as low as 7.59 × 10^-8 mol·L^-1, and the binding ratio of the APA probe with Au³⁺ ions was 2:1. Therefore, the APA probe has potential applications for detecting Au³⁺ ions in the environment and in living organisms.