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Voltammetric sensor using a symmetrical derivative of anthrone3 (1,7-diamino-3,9-dibutyl benzo[1,2,3-de:4,5,6-d’e’]diquinoline-2,8(3H,9H)-dione) (SPE-A) has been developed as a probe for Hg(II) ions. Performance of the probe as screen-printed electrode modified with the receptor (SPE-A) has been compared with anthrone3 in solution phase, using 1:1 water-acetonitrile solvent system. Anthrone3 displayed an electrochemically quasi-reversible nature in voltammograms with both the systems and is presented as a novel disposable voltammetric sensor for mercury ions. Upon interaction with cations, both the electrode systems showed sensitivity towards Hg2+ ions with a lower detection limit of 0.61 µM. The magnitude of the voltammetric current with the SPE-A exhibited three times the current obtained with a bare glassy carbon electrode (GC). Kinetic performance of the SPE-A electrode is better than the GC electrode. The morphological studies indicate reusability of the electrodes.

A new fluorescence receptor (E)-2-amino-N′-((3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl)methylene)benzohydrazide (1) was synthesized by reacting vitamin B6 cofactor pyridoxal with 2-aminobenzohydrazide, and characterized by various spectral (FT-IR, 1H NMR, 13C NMR and ESI-MS) data. It shows high selectivity and sensitivity towards Zn2+ and CN− ions among the other tested metal ions (Cu2+, Co2+, Ni2+, Mn2+, Mg2+, Fe3+, Fe2+, Cd2+, Hg2+, Pb2+, Al3+ and Cr3+) and anions (F−, Cl−, Br−, I−, NO3−, N3−, HSO4−, H2PO4−, ClO4− and AcO−). With the addition of Zn2+ and CN−, the receptor 1 displays a drastic fluorescence enhancement around 475–480 nm without any interference from other tested cations/anions. Receptor 1 shows the detection limit down to 3.20 ×10−7 M and 1.53×10−7 M for Zn2+ and CN− ions, respectively. In addition, the receptor 1 shows selective response towards CN− by giving a new absorption band around 431 nm. The recognition mechanism was proposed through 1H NMR and DFT results. Finally, the receptor 1 was applied for the detection of bioactive Zn2+ ions in live HeLa cells.

A novel fluorescent receptor L was synthesized by Schiff base condensation of 1-pyrenemethylamine with the vitamin B6 cofactor pyridoxal. The receptor L is highly selective and sensitive towards Zn2+ ions among other tested metal ions. Upon interaction with Zn2+, the receptor L showed a distinct fluorescence enhancement at 485 nm due to the excimer formation leading to the fluorescent colour change from blue to bluish-green. Subsequently, when the in situ generated ZnL2 complex interacted with various anions and amino acids, the addition of H2PO4− and cysteine reinstated the fluorescence of the receptor L due to the demetalation of Zn2+ from the ZnL2 complex. Accordingly, the receptor L was developed for the highly selective, specific and sensitive detection of three important bioactive analytes, i.e., Zn2+, H2PO4− and cysteine with a detection limit down to 2.3 × 10−6 M, 2.18 × 10−7 M and 1.59 × 10−7 M, respectively. Additionally, the receptor L was applied to the detection of intracellular Zn2+ ions in live HeLa cells.