Histidinehydroxamic acid as new biomolecule to produce molecular-like fluorescent gold nanoclusters: Possible mechanisms for metal ion sensing

Gombár, Gyöngyi and Simon, Péter and Ungor, Ditta and Szatmári, István and Csapó, Edit (2023) Histidinehydroxamic acid as new biomolecule to produce molecular-like fluorescent gold nanoclusters: Possible mechanisms for metal ion sensing. JOURNAL OF MOLECULAR LIQUIDS, 387. ISSN 0167-7322

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Abstract

We firstly demonstrate a new biomolecule, Histidinehydroxamic acid (HisHA), to produce few-atomic fluorescent gold nanoclusters (Au NCs) in aqueous medium. The preparation protocol has been optimized by studying the effect of metal ion/biomolecule molar ratio, metal ion concentration, pH, temperature, reaction time as well as the role of citrate as mild reducing agent on appearance of blue-emitting (λem = 440 nm, λex = 365 nm) molecular-like NCs. Structural studies confirmed that imidazole-N and amino-N of the HisHA stabilize the formed metallic cores. The quantum yield of ~ 4% and fluorescence lifetime of 4.2 ns were determined. Moreover, these NCs show suitable stability under high inert salt (cNaCl = 2.5 M) concentration as well. Verifying its ability to detect metal ions, dual strategies were discovered. We confirmed that the copper ions cause fluorescence quenching (LOD = 2.49 µM) by pushing the higher amount of soft HisHA ligand from the metallic surface and forming complexes with dominantly hydroxamate-[O,O] coordination mode in the aqueous medium. For Zn2+- ions, a “turn-on” sensing mechanism was observed; the smallest detectable amount of Zn2+ is 7.5 µM. Linear increase of the quantum yield (from ~ 4% to ~ 11.5%) was identified above 75 μM of Zn2+ due to the binding of the Zn2+-ions on the cluster surface via hydroxamate-[O,O] donors.

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