Electrochemical Hg²⁺detection at tannic acid-gold nanoparticle modified electrodes by square wave voltammetry

Abstract

We report the electrochemical sensing of Hg2+ based on tannic acid capped gold nanoparticle (AuNP@TA) complexes. At optimal conditions using square wave voltammetry, the presented analytical method exhibits a "measurable lower limit" of 100.0 fM. This limit is considerably below the permissible level of 30.0 nM for inorganic mercury in drinking water, specified by the World Health Organization (WHO). The effect of potentially interfering ions, such as Zn2+ and Al3+, was studied and results indicate an excellent selectivity for Hg2+. The transfer of the proposed strategy onto AuNP@TA modified screen-printed electrodes demonstrates its applicability to routine monitoring of Hg2+ in tap water.

Tannic acid capped gold nanoparticles: capping agent chemistry controls the redox activity

“…The manufacturer declares 26 that "no residual reactants" are present in the final formulation. Zinc nitrate hexahydrate (Zn(NO 3 ) 2 .6H 2 O ≥98%, Sigma-Aldrich, Gillingham, UK) and mercury(II) nitrate (Hg(NO 3 ) 2 0.05 M, Sigma-Aldrich, Steinheim, Germany) were used as Zn 2+ and Hg 2+ sources, respectively; and were prepared in 0.1 M KCl + 0.1 M HCl solutions 15,16 . All solutions were prepared using nanopure water with a resistivity of not less than 18.2 MΩ cm at 298K (Millipore, US) and degassed thoroughly with high purity nitrogen flow (BOC Gases plc, UK) before use.…”

“…CV analysis of Hg 2+ has been reported previously. 16 For nanoimpacts experiments, the chronoamperometry was recorded at a carbon microdisc electrode with the same reference and counter electrodes as above; but using a home-built low noise potentiostat with a post-acquisition Bessel filtering of 100 Hz and PyFemto software (version 0.6). 30 This potentiostat accurately conserves the overall amount of charge transferred due to a particle impact process despite possible alteration in the spike shape.…”

“…Scanning electron microscopy (SEM) and zeta potential analyses of the AuNPs@TA have been reported previously. 15,16 Meanwhile, a Shimadzu UV-1800 with 20 µL High Precision Quartz Cells (Hellma Analytics, Germany) was used to measure the stability of the 10 pM of AuNPs@TA in various concentrations of supporting electrolyte. Each solution was outgassed prior to the measurement and followed by performing baseline correction.…”

“…These values are consistent with the data supplied by the manufacturer of the particle 26 and with our previous reports. 15,16 The stability of the AuNPs@TA in various concentrations of electrolyte were assessed by UV-Vis spectroscopy, in the range of 10 to 100 mM of KCl + HCl solutions. Each electrolyte was outgassed thoroughly with nitrogen before 10 pM of AuNPs@TA (ca.…”

“…Macromolecular capping agents such as tannic acid (TA) have been exploited for the electrochemical detection of specific metal cations via ensembles of the gold nanoparticles. 15,16 However, the electrochemical analysis of the TA capping agent studied with an ensemble of AuNPs@TA (for example using stripping voltammetry) does not reflect necessarily its behaviour at the individual nanoparticle level. In particular, analysis of the nanoparticles using stripping voltammetry is unreliable because capping agent effects in drop casting may lead to particle aggregation and partial oxidation.…”