Mercaptothiadiazole capped gold nanoparticles as fluorophore for the determination of nanomolar mercury(ii) in aqueous solution in the presence of 50 000-fold major interferents

Abstract

The present work describes the determination of picogram Hg(II) using 2,5-dimercapto-1,3,4-thiadiazole stabilized gold nanoparticles (DMT-AuNPs) by a spectrofluorimetry method. DMT-AuNPs show emission maximum at 773 nm with excitation at 514 nm. They show a large stock shift (259 nm), narrow emission profile and good photostability. While adding 10 μM Hg(II) the red color solution of DMT-AuNPs changes to purple and the UV-visible spectrum of DMT-AuNPs band at 514 nm was decreased. This is due to aggregation of DMT-AuNPs and it was confirmed by high resolution transmission electron microscopy (HR-TEM). UV-visible spectra of DMT-AuNPs in the presence of nanomolar concentrations of Hg(II) do not show any significant changes at 514 nm. However, the emission intensity of DMT-AuNPs was enhanced during adding even at picomolar concentration of Hg(II) due to photoinduced electron transfer and metal binding-induced conformational restriction upon complexation. Based on the enhancement of emission intensity the concentration of Hg(II) was determined. The binding constant (K(A) = 2.6514 × 10(4) mol(-1) L) value suggested that there is a strong binding force between Hg(II) and DMT-AuNPs. The present fluorophore showed an extreme selectivity towards Hg(II). The emission intensity was increased linearly against a wide range of Hg(II) concentration from 1 × 10(-12) to 1 × 10(-7) M and a detection limit of 0.64 pg L(-1) Hg(II) (S/N = 3) was achieved for the first time using DMT-AuNPs by spectrofluorimetry method. The proposed method was successfully applied for the determination of Hg(II) in environmental samples. The obtained results were validated by ICP-AES.

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“…It shows a large stock shift (λ em -λ ex = 261 nm). The obtained narrow emission profile and large stock shift indicate that AHMP-AuNPs are highly fluorescent [26]. Further, we have monitored the stability of the AuNPs by UV-visible spectroscopy.…”

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Optical Reading of Contaminants in Aqueous Media Based on Gold Nanoparticles

“…[ 165 ] Besides, a series of thio group and amino group involved fi ve-membered heterocycle molecules (e.g. 2,5-dimercapto-1,3,4-thiadiazole, 3,5-diamino-1,2,4-triazole, and 3-amino-5-mercapto-1,2,4-triazole) were also introduced in AuNPs system and applied in fl uorescent detection of Hg 2+ [ 166 ] and melamine [ 167 ] with great sensitivites, respectively.…”