Chlortoluron-induced enzymatic activity inhibition in tyrosinase/ZnO NPs/SPCE biosensor for the detection of ppb levels of herbicide

• Straightforward electrochemical nanostructuration of SPCEs with ZnO nanoparticles.
• Adsorption of tyrosinase is favored by the high ZnO IEP of ZnO-nanostructured SPCEs.
• Sensitive detection of sub-micromolar levels of phenol based on quinone reduction.
• ppb Levels of chlortoluron based on chlortoluron-induced tyrosinase inhibition.
• Reversible inhibition allowing multiple uses of the biosensor.

Concerns about human health are increasingly growing because of the widespread use of herbicides and pesticides which requires the development of fast, reliable and cost-effective methods for their detection. In this work, we report the design of a disposable yet very sensitive enzymatic biosensor for chlortoluron, a widely used herbicide in cereal fields, based on herbicide-induced inhibition of tyrosinase activity. The sensing platform is formed tyrosinase-modified screen-printed carbon electrodes (SPCEs) electrochemically nanostructured by ZnO nanoparticles. The stepwise surface modification was assessed by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The modified electrode can selectively detect phenol ranging from 0.1 to 14 μM with a sensitivity of 18.71 nA/μM and a limit of detection of 0.02 μM. In presence of chlortoluron, the enzyme activity is proportionally inhibited in respect to the herbicide concentration. The biosensor shows linear relationship (r > 0.998) of the inhibition levels from 1 to 100 nM with a limit of detection of 0.47 nM (∼0.1 ppb).

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