Study On High Sensitive Electrochemical Detection Of Avian Leukemia Virus And Efifcient Control Technoloies Of Pathogenic Bacteria

In recent years, subgroup J of avian leukosis virus （ALVs-J） has caused enormouseconomic losses in chicken worldwide. It is imperative to develop the novel efficient andconvenient techniques to detect and control the pathogenic microorganism. To date, severaltraditional methods for the quantification determination of ALVs-J normally require severaldays and higher costs to complete the processes. Electrochemical immunoassay has arousedmuch attention due to its advantages in terms of rapid, accurate, high sensitivity, low-cost andgood reproducibility. In addition, Escherichia coli （E.coli） and Staphylococcus aureus（S.aureus） are typical examples of waterborne pathogen in drinking water, which commonlycause gastrointestinal illness and infectious diseases in humans. This problem has got widepublic concern at present. Traditional disinfection methods could lead to the production oftoxic byproducts, pollution of environment and low utilization of energy. It is critical todevelopment more effective disinfection technology to realize the efficient control ofpathogenic bacteria. Based on a variety of functionalized nanomaterials, in this paper, threenovel electrochemical immunosensors were designed for ultrasensitive detection of ALVs-Jand two kinds of new efficient control technologies were developed towards E.coli andS.aureus.（1） A novel electrochemical immunosensor for ultrasensitive detection of ALVs-J wasdesigned by using graphene sheets （GS）-layered double hydroxides （LDHs） nanocompositemodified electrode with multifunctional Fe₃O₄core/Ni-Al LDHs shell （LDHs@Fe₃O₄）nanospheres as labels. At first, the GS-LDHs was used for the immunosensor platform forimproving the electronic transmission rate as well as increasing the surface area to capture alarge amount of primary antibodies （Ab1）. After that, ferrocene （Fc）, secondary antibodies（Ab₂） and horseradish peroxidase （HRP） multifunctional LDHs@Fe₃O₄nanospheres wereused as labels with high load amount and good biological activity. Subsequently, in presenceof H₂O₂, amplified signals were obtained by an electrochemical sandwich immunoassayprotocol. To embody the signal amplification property of the protocol, the analyticalproperties of various immunosensor platform and labels were compared in detail. Underoptimal conditions, the reduction peak currents of the electrochemical immunosensor wereproportional to the ALVs-J concentration over the range from102.32to105.50TCID₅₀/mL(TCID₅₀:50%tissue culture infective does) with a low detection limit (180TCID₅₀/mL, S/N=3). The resulting immunosensor also displayed a good selectivity, reproducibility and stability.（2） A novel sandwich-type electrochemical immunosensor was fabricated for ultrasensitive detection of ALVs-J by employing cyclodextrin （CD）-ferrocene host-guestcomplex multifunctional Fe₃O₄nanospheres as labels and cyclodextrin functional graphenesheets （CD-GS） nanocomposite as sensor platform. The sensitivity was greatly improvedbased on the triple amplification strategy. Firstly, the CD-GS improved the electron transferrate as well as increasing the surface area to capture a large amount of Ab1. Secondly, the CDon the Fe₃O₄surface with strong recognition capability could form stable CD-Fc host-guestinclusion complex and provided larger free room for the conjugation of Ab₂and glucoseoxidase （GOD）. Finally, the conjugated GOD exhibited extraordinary electrochemicalbiocatalysis towards the reduction reaction of Fc⁺by glucose. Under the optimized conditions,the electrochemical immunosensor exhibited a wide working range from10^2.27to10^3.50TCID₅₀/mL with a low detection limit of10^2.19TCID₅₀/mL （S/N=3）. The selectivity,reproducibility and stability were acceptable. The assay was evaluated for real avian serumsample, receiving satisfactory results. This new type of triple amplification strategy mayprovide potential applications for the clinic application.（3） A glassy carbon electrode （GCE） was modified with a film of poly（3-thiopheneboronic acid）（PTBA）-gold nanoparticles （AuNPs）-graphene nanocomposit and the antibody（Ab） was immobilized on its surface through the covalent bond formed between the boronicacid group and the glycosyl groups of the Ab. ALVs-J were electrochemically determinedwith the help of this electrode. There was a linear relationship between the electron transferresistance （Ret） and the concentration of ALVs-J in the range from527to3162TCID₅₀ mL-1with the detection limit was210TCID₅₀/mL （S/N=3）. This electrochemical immunoassayshowed a good selectivity, stability and reproducibility.（4） Novel poly-（3-thiopheneacetic acid）（PTAA） coated LDHs@Fe₃O₄photocatalyst wasprepared and used for photocatalytic disinfection of pathogenic bacteria under solar lightirradiation. The influence parameters of photocatalytic antibacterial activity ofPTAA-LDHs@Fe₃O₄photocatalyst were optimized against E. coli and S. aureus. Resultsshowed that PTAA-LDHs@Fe₃O₄photocatalyst could effectively absorb the ultraviolet andvisible light. The antibacterial rates could achieve99.99%irradiated by solar light with0.8mg/mL PTAA-LDHs@Fe₃O₄during140min. Moreover, it was confirmed that hydroxylradicals （OH） were generated during the photocatalytic process, which was the majorresponsibility for the photocatalytic disinfection. The destruction of bacteria cells structureduring the bactericidal procedure was observed by transmission electron microscopy （TEM）.The novel photocatalyst could have potential applications in the related bactericidal fields.（5） This work reported an efficient electrochemical treatment for water disinfection using a pyrolytic graphite electrode （PGE） modified with ferrocenyl tethered poly（amidoamine）dendrimers （FcD）-multiwalled carbon nanotubes （MWCNT）-chitosan （Chit） nanocomposite.The influence parameters of electrochemical disinfection of E.coli and S.aureus, such asapplied potential and sterilization time, were investigated. Further investigation indicated thatalmost all （99.99%） of the initial bacteria were killed after applying a low potential of0.4Vfor10min. During the electrochemical disinfection process, the oxidized form of ferrocenewas formed on electrode, which played a key role in the disinfection towards E.coli andS.aureus. Hence, the proposed method may provide potential application for the disinfectionof drinking water.