Structure-switching of an organothiol neutral carrier by gold nanoparticles decorated on SH-MWCNTs for ultra-trace voltammetric assay of Hg(ii) using a carbon paste electrode

Abstract

A simple strategy has been developed based on 1,2-bis[5,2-thiolmethyl-sulphide-1,3,4-oxadiazol-2-yl]ethane (BTMSOE) as a novel ion-carrier for construction of a voltammetric Hg(II)-CPE. AuNPs not only have strong inter-particle binding affinity (Au–Au), but also have strong tendency to form S–Au covalent bonds with –SH functional groups. In view of this fact, by self-assembling of AuNPs, the spatial configuration of the thiol-terminated BTMSOE compound was switched from podant to macrocycle-type ligand. The macrocycle-type BTMSOE–AuNP compound was then immobilized by self-assembly on the super-conductive MWCNT substrate via a (3-mercaptopropyl) trimethoxysilane (MPTS) covalent linker. Under the optimized conditions, the oxidative current I_p,a (μA) exhibited a linear dependence on Hg(II) ion concentration in the wide dynamic concentration ranges of 3.5 × 10⁻¹¹ to 3.7 × 10⁻⁷ M and 1.2 × 10⁻⁶ to 1.0 × 10⁻⁴ M (R² = 0.9947 and 0.9992, respectively). Moreover, the limit of detection of the proposed sensor was 1.7 × 10⁻¹² mol L⁻¹ (S/N = 3) at a working optimal pH of 4.2 adjusted by ABS as an appropriate supporting electrolyte. These features, specifically the high sensitivity and exceptional selectivity, were positively compared with those of previously reported methods in the area of electrochemical Hg(II) detection. Eventually, the practical utility of the prepared MWCNTs/AuNPs/BTMSOE-CPE was assessed for efficient determination of Hg(II) contents in aqueous environmental samples with different matrices such as tap and mineral water, tuna fish, human hair, and tobacco.