Mercury (II) off-on luminescence chemosensing based on the incorporation of Rhodamine 6G spirocyclic phenylthiosemicarbazide derivative in Au nanoparticles

A. MUÑOZ DE LA PEÑA; M.J. CULZONI; M.C.ONAINDIA; R.BRASCA; H.C. GOICOECHEA

Congreso; XXV National Spectroscopy Meeting (XV RNE) and IX Iberian Spectroscopy Conference (IX CIE); 2016

On the basis of the maximum level (2 ng mL-1) of mercury in drinking water permitted by the United States Environmental Protection Agency (EPA), an ideal probe should display a very low detection limit and a high selectivity towards Hg2+ in the presence of other metals [1]. Considerable attention has been recently focused on the design of luminescence chemodosimeters for mercuric ion due to the highly sensitive, quick, and nondestructive advantages of luminescence methods. The chemodosimeter strategy is based on the use of a selective reaction that is induced by the target species and gives rise to an observable luminescence signal (preferably off-on). Rhodamine and BODIPY derivatives are two families of small molecular probes reported for selective Hg2+ detection [2]. Rhodamine 6G spirocyclic phenylthiosemicarbazide derivative (FC1) has been previously proposed for Hg2+ determination in diverse matrices, as water and fish samples [3,4], and the procedure improved by immobilization of the reagent in nylon membranes [5], hydrophilic water-insoluble poly(2-hydroxyethylmethacrylate-co-methylmethacrylate) [6] and electrospinning generated microfibre nonwoven mats [7].The purpose of this work is to enhance the sensitivity of the reaction of FC1 towards Hg2+ by coupling the probe to Au nanoparticles, maintaining its high selectivity.Au nanoparticles were synthesized by reduction of AuCl3 with sodium citrate and characterized by DLS (Dynamic Light Scattering). In the presence of the Au nanoparticles FC1 exhibits lower fluorescence than in its absence due to an intense resonance energy transfer (RET) effect. This fact improves the sensitivity of the reaction towards Hg2+, allowing its determination at concentrations below 2 ng mL-1.The chemodosimeter has been applied to the determination of traces of Hg2+ in different aqueous samples. The proposed method allows the determination of Hg2+ in a variety of aqueous samples, in a fast, economical and simple way. The emission of fluorescence was measured at 555 nm, by exciting at 528nm, in the interval between 0.5 and 10 ng mL-1, with a detection limit of 0.15 ng mL-1, being 5 times more sensitive than the original method in absence of the Au nanoparticles [3].