Vanillin-coumarin hybrid molecule as an efficient fluorescent probe for trace level determination of Hg(II) and its application in cell imaging

An efficient Hg²⁺ selective fluorescent probe (vanillin azo coumarin, VAC) was synthesized by blending vanillin with coumarin. VAC and its Hg²⁺ complex were well characterized by different spectroscopic techniques like ¹H NMR, QTOF-MS ES⁺, FTIR and elemental analysis as well. VAC could detect up to 1.25 μM Hg²⁺ in aqueous methanol solution through fluorescence enhancement. The method was linear up to 16 μM of Hg²⁺. Negative interferences from Cu²⁺, Ni²⁺, Fe³⁺, and Zn²⁺ were eliminated using EDTA as a masking agent. VAC showed a strong binding to Hg²⁺ ion as evident from its binding constant value (2.2 × 10⁵), estimated using Benesi-Hildebrand equation. Mercuration assisted restricted rotation of the vanillin moiety and inhibited photoinduced electron transfer from the O, N-donor sites to the coumarin unit are responsible for the enhancement of fluorescence upon mercuration of VAC. VAC was used for imaging the accumulation of Hg²⁺ ions in Candida albicans cells.