Electrochemical detection of glyphosate herbicide using horseradish peroxidase immobilized on sulfonated polymer matrix

This paper describes the use of horseradish peroxidase (HRP) based biosensor for novel detection of glyphosate herbicide. The biosensor was prepared by electrochemically depositing poly(2,5-dimethoxyaniline) (PDMA) doped with poly(4-styrenesulfonic acid) (PSS) onto the surface of a gold electrode followed by electrostatic attachment of the enzyme HRP onto the PDMA-PSS composite film. Fourier transform infrared (FTIR) and UV-Vis spectrometry inferred that HRP was not denatured during its immobilization on PDMA-PSS composite film. The biosensing principle was based on the determination of the cathodic responses of the immobilized HRP to H₂O₂, before and after incubation in glyphosate standard solutions. Glyphosate inhibited the activity of HRP causing a decrease in its response to H₂O₂. The determination of glyphosate was achieved in the range of 0.25-14.0 μg L^{- 1} with a detection limit of 1.70 μg L^{- 1}. The apparent Michaelis-Menten constant (calculated for the HRP/PDMA-PSS biosensor in the presence and absence of glyphosate was found to be 7.73 μM and 7.95 μM respectively.