Effect of AgNPs internal solution on the sensing of mercury(II) by an ion-selective electrode based on a thiol coordination from cysteine as ionophore

The use of nanoparticles in the sensing of mercury from environmental and biological fluids is limited to optical and colorimetric sensors. The present research investigates the use of starch capped silver nanoparticles (SAgNPs) as the internal solution of an ion-selective electrode (ISE) of mercury(II) using a PVC selective membrane incorporating cysteine as ionophore. SAgNPs are synthesized by the reducing method showing a 4.13 nm/diameter and a zeta potential of +33.03 ± 4.0 mV. The lattice structure of SAgNPs is identified as face-centered cubic (FCC) by using XRD analysis. HRTEM micrograph and contrast intensity profile confirms the Ag atomic lattices at 2.35 Å and 2.03 Å corresponding to (1 1 1) and (2 0 0) hkl plane. Hg²⁺ was sensed by the SAgNPs internal solution in the nano-molar range with a limit of detection of 0.34 nM. The potentiometric determination of Hg²⁺ using the ISE based on cysteine as ionophore and the SAgNPs as internal solution (ISE-SAgNPs) allows the sensing of mercury in the nanomolar level within a wide range concentration of mercury (5.1 × 10⁻⁸ to 1.1 × 10⁻¹ M) with a detection limit of 1.5 × 10⁻⁸ M, a limit of quantitation of 5.1 × 10⁻⁸ M and a Nernstian behaviour with a slope of 29.42 ± 0.75 mV. The ISE-SAgNPs works perfectly within a 0–7 pH with high selectivity towards Hg²⁺ and within a 17 s response time.