Ultra-sensitive electrochemical sensors based on self-assembled chelating dithiol on gold electrode for trace level detection of copper(II) ions

Abstract Humans are exposed to copper via contaminated drinking water/food and other environmental sources which pose an increasing threat to healthy functioning of life-sustaining metabolic activities and demands regular monitoring of copper content in the environment, i.e. soil and water. In the present work, chelating dithiol, bis(3-((5-mercapto-1,3,4-thiadiazol-2-yl)carbamoyl)phenyl)terephthalate (BMTCPT) was synthesized and self-assembled on the surface of gold electrode which allows the formation of macrocycle capable of accommodating metal ions. Self-assembly of dithiol was confirmed by electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in two redox probes: anionic, [Fe(CN)6]3-/4- and cationic, [Ru(NH3)6]2+/3+ and further, utilized as a platform for impedimetric sensing for Cu2+. EIS studies showed that Au-BMTCPT electrode displayed a very sensitive and selective response towards Cu2+ in wider linear concentration range from 1 × 10-12 M to 1 × 10-5 M (r2 = 0.990) at pH = 5 with lower detection limit of 9.7 × 10-13 M. In addition, dithiol self-assembled gold nanoparticles (BMTCPT-AuNPs) were applied to construct a chemically modified carbon paste electrode (CPE) and subjected to potentiometric detection of Cu2+ which exhibited a Nernstian slope of 29.85 ± 0.2 mV per decade in concentration range of 1 × 10-9 M - 1 × 10-4 M (r2 = 0.999) with a detection limit of 8.91 × 10-10 M.