Study of the interaction of β-carbolines with gold nanoparticles and its application to turn-on fluorescence detection of silver ion

The interaction of harmine and harmane, two important members of β-carboline alkaloids, with gold nanoparticles (Au NPs) was investigated by fluorescence spectroscopy. Au NPs strongly quench the intrinsic fluorescence of these alkaloids as a result of resonance energy transfer. The Stern–Volmer plots were evaluated and corresponding Stern–Volmer quenching constants were found to be 5.3 × 109 and 6.4 × 109 M−1 for harmine and harmane, respectively. The analytical applicability of β-carboline-Au NP systems was explored and found that they can be used for turn-on fluorescence detection of silver ions at ultra-trace levels. Using harmine-Au NP system, the calibration graph for silver ion was linear in the range of 9.0–470 μg L−1 with a limit of detection of 5.0 μg L−1. The developed method was applied to the determination of silver in real water samples.