Sensors Based On Nanomaterial Macroscopic Composites For The Detecction Of Organophosphorus Pesticides

Pesticides have been widely utilized to protect crops against insects and pests in modern agriculture.Nevertheless,due to the inherent toxicity and misuse-caused accumulation in the food chain and environment,pesticide residues bring horrific effects on agricultural safety,human health and environment.Therefore,it is of great importance to detect pesticide residues with high efficiency,simplicity and convenience.Being highly sensitive and fast,nanomaterials（NM）-based biosensors/chemosensors（sensors）have been emerging as one of the most promising tools for the detection of pesticides.However,the direct application of NM powders in sensors is not only inconvenient for the operation,but also lowly effective for the improvement of performance,which is becoming one of the most crucial bottlenecks of the field.In order to solve the above problems,this dissertation proposes a noval strategy of integrating diverse NM elements into one macroscopic composite（nanomaterial macroscopic composite,NMMC）to develop sensors for the rapid,facile and sensitive detection of pesticides.Using organophosphorus pesticides（OPs）as the model targets,three different NMMC-based sensors were developed with the consideration of the elemets,the methods for the combination/integration of elements,and the synergistic mechanism of elements in function.These sensors present not only improved performance in the efficiency,convenience and sensitivity,but also the potential for the detection of OPs in agro-product samples（e.g.rice）.The main research contents are as following:（1）From the perspective of higly efficient integration of NM elements in one sensor to improve the performance,a fast and simple preparation method for Fibrin-NM composite hydrogel（CH）has been developed,by taking advantage of the high integration characteristics of Fibrin in physiological blood-coagulation.The obtained Fibrin-NM CH presents as the 3D porous network loaded with numerous elements,proving that this method possesses high integration capability to diverse elements,ranging from enzymes to NM with different sizes and properties.Besides,Fibrin-r GO（reduced graphene oxide）composite film（CF）was also obtained on the basis of the proposed method.Benefiting from the unique integration method and the synergy of Fibrin and r GO,Fibrin-r GO CF was endowed with high conductivity of 26.9S m^-1,as well as good mechanical strength,stability,adhesiveness to different surfaces,paying the fundamention for the preparation of NMMC-based electrochemical sensors with high integration degree and excellent performance.（2）Taking advantage of the proposed method in（1）,a Fibrin-r GO CF-based electrochemical sensing platform has been designed and fabricated.Firstly,two classic catalytic systems were selected as the models for verification,i.e.,the synergistic catalysis of r GO and platinum nanoparticles（Pt NPs）for the electrochemical oxidation of H2O2,and the cascade catalysis of glucose oxidase（GOx）and r GO-Pt NPs for the oxidation of glucose.Results indicated that the platform not only was favorable for the retection of the activities/functions of each elements,but also possessed the potential for synergistic and cascade catalysis.Taking the above into the consideration,an acetylcholinesterase（ACh E）-inhibited electrochemical biosensor was constructed based on Fibrin-r GO-ACh E CF modified Au electrode.Benefiting from the synergistic load of ACh E by highly-adhesive Fibrin and r GO with large surface area,as well as the cascade catalysis of ACh E and r GO for signal amplification,the biosensor was sensitive,fast and reliable for the detection of paraoxon,with the Limit of detection（LOD）of0.2μg L^-1 and linear detection range（LDR）of 0.5-15μg L^-1 and 15-37.5μg L^-1.Comparing with analogous sensors prepared by conventional methods,this biosensor exihibited advantages in integration,convenience and performance for the detection.（3）To avoid the problems brought from ACh E in part（2）,e.g.,high cost and inadaptability of the biosensor for practical application,a fluorescent metal-organic frameworks（MOFs）nanoprobe（Zr-LMOFs）has been prepared.It was sensitive for the detection o methyl parathion（m-PT）with LOD of 3.15μg L^-1 and LDR of 25-1500μg L^-1,which decreased the cost for elements.Furthermore,based on the method developed in part（1）,using Fibrin as the linkage,Zr-LMOFs was loaded on melamine sponge and a fluorescent sensor of Zr/F/MS was constructed.For the detection of m-PT,the LDR of Zr/F/MS was 100-2000μg L^-1,and LOD was 5.35μg L^-1.Besides,the sensor also exhibited outstanding anti-interference capability towards four types of OPs,two types of non-OPs and two types of inorganic ions.The spiked recovery rates of real rice samples were 95.1-107.5%.Furthermore,Zr/F/MS performed well in p H 5 or 10%Et OH solution,or at 50℃,proving its excellent adaptability in non-neutral buffer solution,extracting solution of sample pre-treatment with some content of organic solvents,and high temperature environment.Therefore,Zr/F/MS not only improve the practicability of Zr-LMOFs powders,but also exhibited promising potential for in-site detection of m-PT in practical scenarios,comparing with ACh E-based biosensors.（4）Although MOFs possesses outstanding potential for sensing,the preparation of MOFs-NMMC（e.g.Zr/F/MS in part（3））is still complicated,time-consuming,and energy/raw material-intensive,which results in high cost but low reproducibility of current sensors.Based on the localized Joule heating of graphene film（GF）,a highly-efficient method was developed for the preparation of MOFs/G（graphene）composite film（CF）.HKUST-1/G CF was firstly selected as the model to investigate the process,influence factors and mechanism of the method.Benefitting from the synergy of localized high temperature and solvent evaporation for the nucleation and growth of MOFs,the time for the preparation of MOFs/G CF can be reduced by at least 4 orders of magnitude,and the demand of raw materials reduced by 2 orders of magnitude,comparing with current methods.This implied the cost for the construction of MOFs-NMMC-based sensor can be reduced sharply.Besisdes,the method was general and can be extended to the preparation of other MOFs/G CFs in one second.The proposed Zr-LMOFs/G-CF-based fluorescent sensor exhibited stability for the load of Zr-LMOFs,and for the detection of m-PT,the LDR was 100-1000μg L^-1,and the LOD was 11.3μg L^-1.Besides,owing to the miniaturization and multi-functions,these CFs can be easily integrated into or developed as the portable sensors,presenting attractive potential in portable and high-throughput detection.