The influence of modifier content on CPE electrode was also evaluated, by which equivalent amounts of rGO and AB4 ranged between 0 and 40% of the total electrode mass. Fig. 3b and Fig. S4 show that the increase in the amount of modifier reaches a maximum current at 30% (m/m) with 15% (m/m) of rGO and 15% (m/m) of AB4. The more modifier content increases, higher is the presence of oxygenated sites available to interact with the paraquat, resulting in improving the sensitivity of the electrode. Therefore, the modifier amount of 30% was selected as the optimal condition to be applied in further experiments, which can decrease the cathodic peak currents due to the presence of more non-conductive material (biochar)