Enzyme Biosensor Based On Carbon Materials For Rapid Detection Of Organophosphate Pesticides

Organophosphate pesticides（OPs）, who have contributed significant economic benefits to society, play an important role in increasing argricultural productivy due to their high insecticidal activity. However, with the incremental utilizations, the OPs residues in water, soil and food can cause long-term damage to the ecological environment and food safety. Therefore, it is very important to establish a rapid and sensitive detection method for pesticide residues. Electrochemical biosensors have been a new way due to their advantages of low cost, simple operation, rapid response and field deployability. Carbon composite materials have many characteristics such as high conductivity, good biocompatibility and larger specific surface area. In this work, porous carbon and honeycomb-like hierarchically ion liquids（[BSmim]HSO₄）-AuNPs-porous carbon composite and nitrogen doped porous carbon was prepared and applied to the detection of OPs. The details are as follows:（1） For purpose of improving the biosensors sensitivity, a sensitive, fast and stable amperometric acetylcholinesterase biosensor was developed based on porous carbon for quantitative determination of OPs. Compared the results of differential pulse voltammetry（DPV） response of acetylthiocholine at different electrodes, the oxidation peak current of thiocholine at AChE/porous carbon/BDD electrode was increased 37.85% than that at AChE/BDD electrode, which improved that the porous carbon has good catalytic performance and electrical conductivity. We have studied the electrochemical behavior of dichlorvos on the AChE/porous carbon/BDD electrode, the conditions for electrode drying and configuration of fixation were optimized. The inhibition rate versus the logarithm of dichlorvos was linear in the range of 1.00×10-9 to 1.00×10-5 g/L,with the detection limit of 6.18×10-10 g/L.（2） In order to solve the problem of the surface of dispersibility and enhance surface adsorption performance, [BSmim]HSO₄-AuNPs-porous carbon composite was prepared for the immobilization of AChE, and a electrochemical biosensor was developed for the detection of dichlorvos. Comparison of Nyquist plots of EIS at different electrodes using [Fe（CN）6]3-/4-as the electrochemical probe. The electron transfer resistance of bare BDD electrode, AuNPs-porous carbon/BDD electrode and [BSmim]HSO₄-AuNPs-porous carbon/BDD electrode was about 483 Ω, 320 Ω and 250 Ω, respectively, suggesting that the presence of porous car-bon, AuNPs and [BSmim]HSO₄ on the electrode surface can improvethe reactive site, reduce the interfacial resistance and make theelectron transfer easier. pH, AChE loading and modified quantity on the response of AChE/[BSmim]HSO₄-AuNPs-porous carbon/BDD biosensor was optimized and best p H is equal to 7.5, optimal amount of enzyme was 0.25 U and optimal amount was 6.00 μL.The inhibition of dichlorvos was linearly proportional to its concentration in the range of 1.00×10-10-1.00×10-6 g/L,with the detection limit of 6.61×10-11 g/L。The sensor could be used for detecting lettuce leaves juice samples, with recovery rate of 80.80%-93.10%. After a 30-day storage in 4℃ refrigerator, the biosensor retained 95.42% of its initial current response.（3） In order to improve the hydrophilicity surface of the electron transfer rate of porous carbon, we introduced the nitrogen atoms into the honeycomb-like hierarchically porous carbon material. Using ionic liquid BMIMdca as precursor, silica spheres as hard templates for preparing nitrogen doped porous carbon material. The AChE biosensor was developed based on nitrogen doped porous carbon modified BDD electrode. The current response of ATCl on the modified electrode was studied, as the result showed, the current of ATCl was proportional to its concentration, with a Michaelis constant of 0.177 mmol/L, which illustrated that the sensor had good enzyme activity.For the detection of dichlorvos and fenitrothion, the as-prepared biosensor showed wide linear ranges of 1.00×10-10-1.00×10-5 g/L, with the detection limits of 1.50×10-12 g/L and 4.42×10-12 g/L, respectively. The average recoveries for practical samples from obtained the AChE/N-doped porous carbon/NBDD sensor were calculated and found to be between 96.13%-100.06% and 90.84%¹07.41% respectively for the detection of dichlorvos and fenitrothion. The sensor had good repeatability, reproducibility, stability, accuracy and acceptable anti-interference ability.