Luzi-Thanfeni, Luleka2025-08-142025-08-142014https://hdl.handle.net/10566/20713In this study, simple, sensitive and low cost electrochemical biosensors for quantitative determination of the carbamate pesticides in real fruit samples have been constructed. Firstly, poly (2.5-dimethoxyaniline) (PDMA) and GO-PANl composite were synthesised on platinum electrode by the electrochemical method using polyvinylsulphonate (PVS) as the dopant for POMA. Fourier transform infrared (FTIR) spectroscopy and UV-Vis spectroscopy studies concluded successful doping of the POMA polymer film by PVS. The biosensor was then constructed by electrostatic attachment of the enzyme, horseradish peroxidase (HRP) onto the surface of the platinum and PDMA-PVS modified electrode. Voltammetric results concluded that HRP immobilised on the Pt/GO-PANI composite and Pt/PDMA-PVS film retained its bioelectrocatalytic activity towards the reduction of H2O2 and was not changed during its immobilisation. The Pt/GO-PANI/HRP and Pt/PDMA-PVS/HRP biosensors were then applied to successfully detect standard carbamate pesticides in a 0.1 M phosphate buffer, 0.1 M PB (pH = 6.8 & 7.2) solution. Various performance and stability parameters were evaluated for the Pt/GO-PANI/HRP and Pt/PDMA-PVS/HRP biosensors. These factors include the optimal enzyme loading, effect of pH and long-term stability of the biosensor on the amperometric behaviour of the biosensor (Songa et al., 2008 and Somerset et al., 2007). The Pt/GO-PANI/HRP and Pt/PDMA-PVS/HRP biosensors were finally applied for the detection of three different carbamates pesticides like carbaryl, carbofuran and methomyl in fruit samples. The biosensing principle was based on determination of the sensor response to the carbamates by amperometric and voltammetric methods. The voltammetric method involved the determination of cathodic responses of the immobilised HRP to peroxide (H2O2), before and after incubation in carbaryl, carbofuran and methomyl standard solutions, respectively. Carbamates pesticides inhibited the activity of HRP causing a decrease in its response to H2O2 as substrate. Carbaryl, carbofuran and methomyl analyses were used on spiked real samples like orange, pear and grapes by amperometric method, within a concentration range of 0.01 - 0.3 mg.L-1 approving that the biosensor is sensitive enough to detect the pesticides in these matrices. The detection limit for carbaryl, carbofuran and methomyl in real fruit samples by amperometric method was determined to be 0.136 mg.L-1, 0.145 mg.L-1 and 0.203 mg.L-1 within a concentration range of 0.01-0.3 mg.L-1. The apparent Michaelis-Menten constant Km (app) calculated for the PDMA-PVS/HRP and GO-PANl/HRP biosensor in the presence and absence of carbaryl were found to be 0.36 μM and 0.17 μM and also 0.07 μM and 0.04 μM respectively. The low Km (app) values obtained for the PDMA-PVS/HRP and GO-PANI/HRP biosensor indicates strong binding to HRP by the substrates. This study demonstrates that the developed biosensor is sensitive enough and could be a useful tool in screening of these pesticides at low concentrations.enConducting polymerOrganic phase biosensorCarbamate pesticidesFruit samplesThesis