Conductive polymer nanocomposite based impedimetric immunosensor for 2,4-dichlorophenoxy acetic acid detection

One of the best promising application field of the biosensors technology is the screening of pollutants in real sample matrices, due to the selectivity towards the analyte and the rapid, reproducible and possibly quantitative or semi-quantitative response. 2,4-Dichlorophenoxy acetic acid (2,4-D) is an auxinic herbicide with grown regulator activity that has been widely used for controlling broadleaf weeds in cereal grain crops. Because of its carcinogenic, teratogenic and estrogenic activity, the presence of residues of 2,4-D in agricultural products and environment can be extremely harmful for both humans and animals. In this work, we developed an impedimetric label free immunosensor for the detection of 2,4-D herbicide either in standard solution and spiked real samples. For this purpose, we prepared by electropolymerisation a conductive poly-(aniline-co-3-aminobenzoic acid) (PANABA) based nanocomposite and then we immobilized anti-2,4-D antibody employing the carboxylic moieties as anchor sites. The nanocomposite was synthesized by electrochemical polymerization of aniline and 3-aminobenzoic acid, in the presence of a dispersion of gold nanoparticles, onto a multi walled carbon nanotubes based screen printed electrode. Aniline-based copolymer, together with the nanomaterials, allowed to enhance the electrode conductivity thus obtaining a wider dynamic impedimetric response and a more sensitive antigen detection. The impedimetric measurements were carried out by electrochemical impedance spectroscopy (EIS) in faradic condition by using Fe(CN)63-/4- as redox probe. The developed impedimetric immunosensor displayed a wide linearity range toward 2,4-D (1-100 ppb), good repeatability (RSD 6%), stability and a LOD (0.3 ppb) lower than herbicide emission limits.