Self-assembled aminothiols: Platforms for ultra-sensitive electrochemical detection of triclosan via surface azo coupling

Abstract

Extensive use of triclosan (TCS) in commercially available personal and health care products has led to its abundance in environment (water, soil), resulting in adverse impact on aquatic, marine, animal and human life. The present work is intended towards the development of simple and fast electrochemical sensors for trace level detection of TCS in aqueous media. The working of sensors is based on surface diazotization of self-assembled monolayers (SAMs) of two aminothiols, 4-aminothiophenol (4-ATP) and 5-amino-2-mercaptobenzimidazole (AMB) on polycrystalline gold electrodes. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), self-assembly of two aminothiols was confirmed as both offered significant impedance to [Fe(CN)6]3-/4− redox probe. The exposed amino groups of two self-assembled aminothiols were subjected to diazotization and diazo derivatives so formed were utilized as platform for impedimetric sensing of TCS through azo coupling. The step-by-step study of self-assembly, diazotization and azo coupling was conducted using different techniques such as FTIR, UV-visible, NMR, FESEM and EDX. The proposed ATP and AMB based EIS sensors exhibited sensitivity towards TCS in wide linear concentration range of 1.0 × 10-10 M – 1.0 × 10-2 M and 1.0 × 10-12 M – 1.0 × 10-4 M with lower detection limits of 5.6 × 10-11 M and 7.9 × 10-13 M, respectively. A good selectivity was observed in the presence of common metal ions (Na+, K+, Ca2+, Mg2+, Cu2+, Fe3+, Zn2+, Co2+) and surfactants (SDS, Triton X-100, Triton X-114). Using proposed EIS sensors, the estimation of TCS in personal care products (soap, facewash, handwash) and water samples (surface and groundwater) has been successfully achieved.