Construction Of Portable Optical Biosensor And Its Application In Pesticide Detection

To meet the urgent needs of smart agriculture construction,food safety supervision and public safety monitoring,the development of efficient,sensitive,and accurate pesticide sensors as agricultural Iot nodes is an important technical support to realize agricultural informatization.Although the traditional techniques(such as chromatography and mass spectrometry)for pesticide detection possessed high accuracy and high sensitivity,high cost,complicated operation,inconvenient carrying and time-consuming procedure restrained its on-site application.Therefore,the development of portable technology suitable for on-site pesticide detection has become the research frontier and hot spot in this field.To solve the key problems of optical enzyme-based biosensor such as high background interference,poor enzyme stability and hard field quantification,this paper prepared a series of novel organic-inorganic sensitive materials to construct highly sensitive and portable optical biosensor for accurate on-site detection of pesticide residues combined with kits and smartphone integration equipment.The main research contents of this paper are as follows:1.A pesticide biosensor based on portable hydrogel kit was constructed,realizing the on-site quantitative analysis of carbaryl.The upconversion nanoparticles(UCNPS)possessed the characteristics of low-energy light excitation and high-energy light emission,which can circumvent background interference from the complex matrix.By using sodium alginate hydrogel to immobilize Na Er F₄:0.5%Tm³⁺@Na YF₄ UCNPS to construct portable kit,dopamine could in situ generate polydopamine on the surface of UCNPS through a self-polymerization reaction,causing the fluorescence quenching of UCNPS.Acetylcholinesterase(ACh E)could catalyze acetylthiocholine into thiocholine and prevent the the self-polymerization of dopamine,which recovered the fluorescence intensity of UCNPS.Furthermore,the fluorescence signal of UCNPS was regulated through the inhibition of ACh E by carbaryl.Based on the sensing principle,the hydrogel portable kit was constructed by using 3D printing technology.Fluorescence images collected by smartphone could be converted into digital signals by computer software,and a quantitative analysis model between color information and pesticide concentration was established,achieving accurate quantitation of carbaryl with the detection limit of 0.5 ng m L^-1.This biosensor possessed the advantages of strong portability and anti-interference ability,which could be successfully applied for the detection of carbaryl residues in eleven kinds of tea samples.2.By using a smartphone-based data acquisition and analysis processing application,a portable detection device for 2,4-dichlorophenoxyacetic acid(2,4-D)pesticide screening was constructed for further reducing the complexity of image processing and improving the integration level and portability.Carbon dots/hydroxyl cobalt oxide nanosheets(CDs/Co OOH)fluorescent composites were prepared by the assembly of the red luminescence characteristics of CDs and Co OOH nanosheets through electrostatic interaction.Alkaline phosphatase(ALP)could catalyze the substrate to yield ascorbic acid(AA),which decomposed CDs/Co OOH fluorescence composite and further enhanced the fluorescence of the system.As an inhibitor of ALP,2,4-D could further regulate the fluorescence response.The smartphone integration equipment was employed to collect the corresponding fluorescence images,and the self-designed smartphone application software can transform image information into digital signals,realizing the quantitative detection for 2,4-D.The portable biosensor could simultaneously realize image acquisition and analysis without the demand of data transmission between smartphone and computer,simplifying image processing procedure and further improving the integration level and portability.3.A highly sensitive pesticide immunosensor based on protein-inorganic hybrid composite(PIHN)was constructed for efficiently immobilizing and improving the the stability of biological enzymes,realizing the quantitative detection of imidacloprid.PIHN with three-dimensional hierarchical structure could immobilize horseradish peroxidase(HRP)and pesticide antibody,not only enhancing the stability of protein,but also boosting the utilization efficiency by regulating the protein distribution position,which improved the sensitivity of immunosensor.Relying on the specific recognition of antibodies and imidacloprid,the PIHN-based immunoassay kit was constructed through colorimetric output mode in a 96-well plate as a carrier.The 50%inhibiting concentration(IC₅₀)was 0.2 ng m L^-1 for imidacloprid,achieving a?105-fold increase in sensitivity compared with the conventional enzyme-linked immunoassay.4.To circumvent monochrome mode output from the instrument and environment error,a dual-color immunosensor for imidacloprid detection was constructed by regulating the morphology and size of enzyme@metal-organic frameworks(MOFs)composite.The influence factors of MOFs microstructure(morphology and size)on the enzyme activity were systematically investigated,improving the stability and sensitivity of immunosensor.Relying on the immunological recognition of antibody and imidacloprid,a dual-color output model was established through the regulation of the gold nanostars etching reaction by biocomposite,that is,the two-channel color change can reflect the information of pesticide concentration,which reduced the error from instrument and environment.Combined with a smartphone for image acquisition,the color information could be converted into digital signals to realize batch detection.The IC₅₀ of imidacloprid was0.48 ng m L^-1,achieving a?50-fold increase in sensitivity compared with the conventional enzyme-linked immunoassay.In summary,this paper constructed portable pesticide biosensors to address the practical problems in pesticide field detection by employing functionalized composite materials,realizing the highly sensitivie detection for pesticide.The development of these portable optical biosensors provided a new idea for the field detection of pesticide.