Highly Sensitive Electrochemical Organophosphate Pesticide Biosensors Based On Mesoporous Materials

Organophorous pesticides are widely used in agriculture for pest control. However, their toxic residuals of OPs in crop, livestock, and poultry products would cause the disfuction of neurotransmitter enzyme, acetylcholinesterase (AChE), and thus harm the human health.Therefore, the development of highly sensitive methods for the detection of organophosphate pesticide is highly desirable. To achieve this goal, two kinds of electrochemical biosensors based on mesocellular foam were fabricated, which showed high sensitivities for the detection of monocrotophos, a highly toxic organophosphate pesticide. Detailed work is as follows:1, Mesocellular silica foam based electrochemical biosensor for highly sensitive sensing of monocrotophos:A sensitive amperometric acetylcholinesterase (AChE) biosensor was fabricated based on mesocellular silica foam (MSF), which functioned as both an enzyme immobilization matrix and a solid phase extraction (SPE) material for the preconcentration of target molecules. The highly ordered mesostructure, good biomputibility, hydrophilicity, large surface area, narrow pore size distribution, which were verified by transmission electron micrograph, nitrogen sorption isotherms, hydrophilic interface and good mechanical/chemical stability of MSF provided the entrapped AChE a good environment to well maintain its bioactivity at basic conditions.As a model, the AChE immobilized in MSF showed improved catalytic ability for the hydrolysis of acetylthiocholine, as evidenced by the increasing of the oxidation current of thiocholine, the enzymatic catalytic hydrolysis production of acetylthiocholine. In addition, the MSF with large surface area showed modest adsorption capacity for monocrotophos, a model organophosphate used in this study, via the hydrogen bond or physical adsorption interaction. The combination of the SPE and good enzyme immobilization ability in MSF significantly promoted the sensitivity of the biosensor, and the limit of detection has lowered to 0.05 ng/mL. The biosensor exhibited accuracy, good reproducibility, and acceptable stability when used for garlic samples analysis. The strategy may provide a new way to fabricate highly sensitive biosensors for the detection of ultra-trace organophophates pesticide infield. 2, Design and synthesis of organically modified mesocellular carbon foam and their application in enhancing enzyme activity and biosensing:An organic group functionalized mesocellular foam (OMCF) was designed and synthesized for the immobilization of acetylcholinesterase. The functionalization of the MCF was achieved through a three step procedure including carboxylation, acylation, and amidation, which has been verified by the IR spectra. The OMCF showed uniformly distributed mesopores, large surface area, and suitable pore size distribution, as characterized by TEM and N2 adsorption/desorption isotherms. The incorporation of functional groups (-phenyl-NH2-) has significantly improved the activity of the entrapped enzyme, which was 1.33 times larger than that of the free enzyme. The resulted biosensor obtained by modification of the OMCF entrapped AChE on the electrode surface showed high sensitivity and low limit of detection, which was lowered down to 0.05 ng/mL. In addition, the biosensor exhibited accuracy, good reproducibility, and acceptable stability when used for garlic samples analysis. Thus, the enzyme immobilization strategy may provide a new method to improve the activity of enzyme and open a new avenue for the fabrication of highly sensitive biosensors.