Sensitive and renewable picloram immunosensor based on paramagnetic immobilisation

Picloram (4-amino-3,5,6-trichloro-2-pyridincarboxylic acid) is one of the chlorinated pesticides. It is widely used for control of wood plants, wheat, barley and wide range of broadleaf weeds as a plant growth regulator. An immunosensor was developed for detection of picloram concentration in compost extracts and river water. The laccase-picloram was prepared. The magnetic core-shell (Fe3O4-SiO2) nanoparticles were modified with anti-picloram-IgG and attached to the surface of carbon paste electrode (CPE) with the aid of paramagnetism. Following competitive immunoreaction with picloram and the picloram-laccase to form immunocomplex, electrochemical measurement was carried out. After immunoassay, the electrode was immersed in glycin-hydrochloric acid buffer or polished with diamond paper for regeneration. The linear range for picloram detection was 1 × 10–4–10 µg mL–1 with the correlation coefficient of 0.9936, and the detection limit is 1 × 10–4 µg mL–1. The laccase labelled on the picloram for competitive immunoassay showed good activity, and the current response was strong and stable in electrochemical detection. The current reached 95% of the steady-state current within about 100 s. The proposed immunosensor exhibited good precision, sensitivity, selectivity, reusability, and storage stability.