Self‐assembly of p‐Aminothiophenol on Gold Surface: Application for Impedimetric and Potentiometric Sensing of Cobalt (II) Ions – A Comparative Study

Abstract

AbstractCobalt, despite an essential biological element, imposes threat to humans when exposed to high concentration or even to low concentration for long term which demands the development of highly sensitive and selective analytical methods for its trace analysis. In the present work, self‐assembly of p‐aminothiophenol (p‐ATP) on gold surface (Au−ATP SAM) was carried out and for the first time, applied as a platform for impedimetric and potentiometric sensing of Co2+. Au−ATP SAM was characterized using electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), in the presence of two redox probes: [Fe(CN)6]3−/4− and [Ru(NH3)6]2+/3+ to evaluate associated passivating behaviour. Au−ATP SAM completely blocked [Fe(CN)6]3−/4− as compared to [Ru(NH3)6]2+/3+ which may be attributed to inner‐sphere and outer‐sphere ET mechanisms, respectively. Au−ATP SAM was found to exhibit excellent sensitivity towards Co2+ in a wider concentration range from 1.0×10−12 M to 1.0×10−5 M (r2=0.963) at pH 5.5 with a detection limit of 6.0×10−13 M and superior selectivity. Further, carbon paste electrode (CPE) was prepared by incorporating p‐ATP bound gold nanoparticles and explored for potentiometric sensing of Co2+ which exhibited Nernstian slope of 29.2±0.2 mV/dec in linear concentration range of 1.0×10−6 M–1.0×10−1 M (r2=0.971) with a detection limit of 8.0×10−7 M. The proposed sensors were successfully applied for estimation of Co2+ content in water samples.