An immunomagnetic electrochemical sensor based an a perfluorosulfonate-coated screen-printed electrode for the determination of 2,4-dichlorophenoxyacetic acid

A disposable immunomagnetic electrochemical sensor involving a magnetic par ticle-based solid phase and a Nafion film-coated screen-printed electrode ( Nafion-SPE) stuck at the bottom of a polystyrene cylinder (microwell of 300 mu L) was developed and evaluated in a competitive immunoassay of the wide ly used herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The competitive b inding of 2,4-D and 2,4-D labeled with alkaline phosphatase (AP) for a limi ted amount of polyclonal anti-2,4-D antibody-coated magnetic beads was moni tored electrochemically by measuring the AP label activity bound to the bea ds. The phosphoric acid ester of [[(4-hydroxyphenyl)amino]carbonyl]cobaltoc enium hexafluorophosphate was used as the AP substrate. This anionic substr ate (S-) is enzymatically transformed at pH 9.0 into a cationic phenol deri vative (pf) which can be easily accumulated in the polyanionic Nafion coati ng and determined by cyclic voltammetry. During the enzyme reaction, the AP -associated beads were localized on the surface of the Nafion-SPE with the aid of a magnet, thus effectively increasing the concentration of P+ in the Nafion-modified electrode vicinity. The enzyme generation of pf close to t he electrode surface, and thereby to the Nafion film, resulted in a high am plification of the response. A detection limit of 0.01 mu g L-1 2,4-D was t hus achieved. The performance of the sensor was successfully evaluated on r iver water samples spiked with 2,4-D, indicating that this convenient and s ensitive technique offers great promise for decentralized environmental app lications.