Amperometric biosensor for glyphosate based on the inhibition of tyrosinase conjugated to carbon nano-onions in a chitosan matrix on a screen-printed electrode.

Glyphosate [N-(phosphonomethyl)glycine] is the most frequently used herbicide to date. Due to its indiscriminate use, it has become a globally occurring pollutant of surface waters. A biosensor for glyphosate is described here that consists of a carbon nano-onion/tyrosinase conjugate immobilized in a chitosan matrix on a screen-printed electrode. The analytical principle is based on the inhibition of the enzyme tyrosinase by glyphosate. L-DOPA is used as the enzyme substrate. The presence of the carbon nano-onions has a beneficial effect on the sensitivity of the assay. Glyphosate can be amperometrically quantified in the 0.015 to 10 μM concentration range and with a 6.5 nM (1.1 μg L-1) detection limit. The biosensor is stable more than 2 months at 4 °C. It was applied to the detection of glyphosate in water and soil samples taken from irrigation of a rice field after aerial application. Results were in good agreement with data obtained by a commercial ELISA. Graphical abstract A highly sensitive amperometric biosensor for glyphosate is reported, based on the covalent immobilization of a carbon nano-onion/tyrosinase conjugate on a chitosan matrix.