Development of electrochemical sensors based on carbon nanomaterials for the detection of carbamate pesticides

This thesis focuses on the development of electrochemical sensors using nanomaterials for the determination of carbamate pesticides which can be divided into three parts. The first part is the development of an electrochemical sensor that measures fenobucarb content by using screen-printed carbon electrode modified with graphene nanoribbons - ionic liquid - cobalt phthalocyanine (GNRs-IL-CoPc/SPCE) nanocomposite and coupled with a flow injection analysis. The results showed that the nanocomposite-enhanced electrodes were responsive to fenobucarb with the highest sensitivity compared to unmodified electrodes due to GNRs and IL being good electrical conductors and CoPc is an excellent electrochemical catalyst. Under optimal conditions, the proposed electrochemical sensor was found to provide a linear range of measurements for fenobucarb at concentrations from 0.025 to 110 μM. The limit of detection and the quantification limit is 0.009 and 0.025 μM, respectively. The second part of the work is the development of disposable electrochemical sensors for the individual and simultaneous determination of carbamate pesticides (carbaryl (CBR), fenobucarb (FNB), and carbosulfan (CBS)). The surface of the screen-printed carbon electrodes was modified with a mixture of graphene nanoplatelets (GNPs) and manganese dioxide (MnO2) nanoparticles. The results showed that the modified electrode was able to catalyze the highest electrocatalytic activity to carbamate pesticide due to the graphene nanoplatelets’ high electrical conductivity and nano MnO2 can catalyze the electrocatalytic activity of carbamate pesticides. The developed sensors provide a linear range for the determination of CBR, FNB, and CBS at concentration ranges of 1-40 μM, 5-150 μM and 50-600 μM with a low detection limit of 0.30 μM, 1.30 μM, and 14.90 μM, respectively. In addition, the analytical performance of disposable sensors for the simultaneous detection of CBR, FNB, and CBS exhibited a linear range of 1–30 μM, 5–80 μM, and 50–400 μM, with the limit of detection at 0.30, 1.40, and 15.15 μM, respectively. The final part of the work was the development of a paper-based electrochemical device (ePAD) for the separation and simultaneous measurement of carbofuran and carbaryl pesticides. The separation of the two carbamate compounds on this device was based on the differences in the movement of the substance on the chromatographic paper during the moving phase flow. The isolated pesticides were electrochemically measured using amperometry techniques. The proposed device provides a linear range for the simultaneous determination of carbofuran and carbonyls from 0.1-2.0 and 0.5-7.5 mg L-1 with the limit of detection were 0.06 and 0.40 mg L-1, respectively.
From all of the above, the proposed sensors could be applied to the measurement of pesticides in real examples: agricultural products (such as Chinese cabbage, cucumbers and rice) and environmental samples (water in the cultivation areas and rivers). The results were satisfactory and consistent with those obtained from the standard method (High-Performance Liquid Chromatography). In addition, the proposed sensors are easy to use, affordable, disposable, portable, and are a promising tool for quantifying pesticides from field samples.