Studies On The Detection Of Organophosphorus Pesticides In Vegetables By Acetylcholineserase Nano-biosensors

With high effieieney of killing pests，the organophosphorus pesticide(OPs) is oneof widely used pesticides in the agriculture. However，because of OPs inhibit theacetylcholinesterase(AChE) participating innerve-impulse transmission, the residua ofOPs had brought serious problems of food safety which became a greater and greaterthreaten to the health of human beings at present. Detection for OPs in food became akey technology of food safety testing. Au nanoparticles (AuNPs) and CdTe quantumdots(QDs), as a typical representative of the noble nanoparticles, which possess manyunique properties. Because of the good optical properties, electrical properties,magnetism properties and so on, AuNPs and CdTe QDs have been widely applied inthe fields of environment, medicine and biology, which have been widely concernedby researchers. In this article, three simple, sensitive and rapid biosensor methodsusing AChE as platform for detection of OPs in vegetables was developed based onthe special properties of nanoparticles.1、Based on the inhibition effects of OPs on AChE, an amperomerometricbiosensor was developed by immobilizing AChE on glassy carbon electrode with thecomposite film of AuNPs and chitosan-silica hybrid sol-gel. Using acetylthiocholinechloride as the substrate, the electrochemical determination method for OPs wasestablished with monocrotophos as a representative model for sensitivity tests. Theexperimental conditions were optimized according to the current response. Theresponse of biosensor fabricated was related linearly to the concentration ofmonocrotophos in the range of0.5~12μg/mL with a detection limit of0.02μg/mL.The developed biosensor exhibited good reproducibility and acceptable stability,providing a simple method for the analysis of OPs.2、With citrate-coated AuNPs as colorimetric probe, a novel visual method forrapid assay of OPs has been developed. The assay principle is based on catalytic hydrolysis of acetylthiocholine into thiocholine by AChE, which induces theaggregation of AuNPs and the color change from claret-red to purple or even grey.The original plasmon absorption of AuNPs at522nm decreases, and simultaneously,a new absorption band appears at675nm. The irreversible inhibition of OPs on AChEprevents aggregation of AuNPs. Under optimum conditions, the absorbance at522nmof AuNPs is related linearly to the concentration of mathamidophos in the range of0.02~1.42μg/mL with a detection limit of1.40ng/mL. This colorimetric method hasbeen successfully utilized to detect mathamidophos in Chinese cabbage withsatisfactory results. The proposed colorimetric assay exhibits good reproducibility andaccuracy, providing a simple and rapid method for the analysis of OPs.3、We have demonstrated the design of a new type fluorescence assay for OPsbased on the inner filter effect (IFE) of AuNPs on the fluorescence of CdTe QDs.With a high extinction coefficient, AuNPs are expected to be capable of functioningas powerful absorbers. QDs with tunable emission wavelength are ideal fluorophoresbecause the emission spectra of the rationally synthesized QDs can perfectly overlapwith the absorption band of the absorber. Mathamidophos are chosen as the modelanalytes, and the IFE-based fluorescent method for detection of mathamidophos wassuggested. Under the optimum conditions, the response is linearly proportional to theconcentration of mathamidophos in the range of0.2~2.6μg/mL with a detection limitof6.84ng/mL. This analysis method has been successfully utilized to detectmathamidophos in real vegetable samples with satisfactory results. The proposedassay exhibits good reproducibility and accuracy, providing a simple and rapidmethod for the analysis of OPs.