A novel pyrazole based single molecular probe for multi-analyte (Zn2+ and Mg2+) detection in human gastric adenocarcinoma cells

Abstract

A new fluorescent sensor, 5-methyl-1H-pyrazole-3-carboxylic acid (6-methoxy-naphthalen-2-ylmethylene)-hydrazide (PYN), composed of a naphthalene group as the fluorogenic unit and a pyrazole carbohydrazide as the binding unit for metal ions has been designed and synthesized. The sensor shows excellent selectivity and sensitivity with a fluorescence enhancement towards Zn²⁺ and Mg²⁺ over other cations in aqueous acetonitrile solution. Turn-on fluorescent enhancements (FE) as high as ∼49 fold and ∼41 fold in mixed media for Zn²⁺ and, Mg²⁺ respectively were noticed. The signal enhancement of the sensor is based on chelation-enhanced fluorescence (CHEF) effect of PYN-Zn²⁺/Mg²⁺ with the inhibition of the photoinduced electron transfer (PET) effect. Moreover, the Job's plot established 1 : 1 stoichiometry of the complex formation between PYN and Zn²⁺ or Mg²⁺ ions. The limit of detection for Zn²⁺ and Mg²⁺ is as low as 2.2 × 10⁻⁷ M and 3.9 × 10⁻⁷ M respectively. PYN exhibited a second mode of selectivity for Zn²⁺ as it displaces Mg²⁺ from the PYN-Mg²⁺ complex. Density Functional Theory (DFT) calculations have been performed in order to show the structure and electronic properties of PYN and its complexes [PYN-Zn²⁺/Mg²⁺]. Cell imaging experiments confirmed that PYN can be used for monitoring intracellular Zn²⁺ and Mg²⁺ levels in living cells in vitro.