A tetra(aniline)-polyethylene glycol block copolymer for efficient electrochemical detection of urea coupled with DFT investigations†

Abstract

This work reports a novel, simple and low-cost block copolymer, poly(ethylene glycol) (PEG) and aniline tetramer (TANI), PEG-TANI-PEG, based electrochemical sensor for the electrochemical detection of urea without utilization of urease enzyme. Urea levels need to be ascertained in humans and soil, as well as in some adulterated dietary stock, as elevated levels may disrupt human metabolic pathways. The block copolymer dispersion in water was drop-cast on fluorine-doped-tin oxide (FTO) glass to develop the working electrode, on which further electrochemical studies were carried out. The electroanalytical techniques of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to investigate the interaction of the PEG-TANI-PEG copolymer with urea under the conditions of optimized scan rate and pH. Results indicate an efficient charge transfer phenomenon between the tetra-aniline units and the analyte, which was subsequently proven by density functional calculations. The designed sensor for urea was effective in a wide linear range of 380–580 μM, with a sensitivity of 0.3468 μA μM⁻¹ cm⁻², a detection limit (LOD) of 254 μM, and a limit of quantification (LOQ) of 770 μM. Furthermore, this work was supported by detailed theoretical studies to evaluate the sensing ability of the oligomers, (EG)_n-TANI-(EG)_n, where the subscript n = 1, 2, and 3 represents increasing ethylene glycol (EG) units. The results of the molecular orbital and AIM analysis on the oligomer–urea complexes reveal that the interaction decreases with the increase in the oligomer chain, primarily due to decrease in the strength of hydrogen bonds.