The Fabrication Of Chemo/Bio-sensors Based On Electronically Conducting Polymers And Its Application In Agricultural Fundamental Research

Agriculture is always the major problems in the national economy and people’slivelihood. Each year, at present, agricultural pollution has not only directly threatento the agricultural safety, but also serious harm to the agricultural ecologicalenvironment and affect human health. Meanwhile, many non-genetic diseases whichhave threaten to human health, are more related to nutritional intake, resulting in awidespread concern in agricultural production and process of nutritional problems offood, vegetables, and agricultural products and its processed products. Traditionaldetection methods such as chromatography, mass spectrometry, spectroscopy andtheir combination methods are sensitive and accurate, but require tedious andtime-consuming sample preparation, professionals to maintain and use, and bulkyinstruments and their expensive costs, which are not suitable for in-field fastmeasurement and real-time on-line analysis. Therefore, the development of a fast,reliable, sensitive and practical monitoring/detection techniques and methods hasimportant practical significance for the agricultural safety and nutrition health.Sensing technology, an important technology in the modern analyticalmethodology, has been widely used in clinical medicine, bio-engineering, foodindustry, environmental testing and other areas due to its low price, simplepreparation, easy operation, high sensitivity, fast response, good selectivity,miniaturization, and continuous on-site detection. However, how to select effectiveimmobilized method of biologically-active speciesthe and appropriate chemo/biosensing materials in the fabrciation of biochemical sensors, which play a crucial rolein important performance parameters such as the stability, sensitivity, and selectivityof chemo/bio sensors. Electronic conductive polymer （ECPs）, especially polyaniline（PANi）, polypyrrole （PPy）, polythiophene （PTh） and their derivatives or compositematerials, have shown a unique charm in the application of efficient chemo/biosensors due to their unique advantages such as reversible electrochemical doping anddedoping, high stable electrical conductivity, molecular wire effect, the combinationwith other different immobilized methods, and the co-deposition or composite with avariety of materials. Inspired by these aspects, new ECPs sensing materials weresynthesized or ECPs composite sensing materials were prepared, and the fabrication,properties and appl ications in agriculturre of various ECPs chemo/bio sensors werestudied by different electrochemical or optical methods. The details are as follows:（1） A variety of enzyme sensors based on ECPs such as PPy, poly-3-thiophene acetic acid （PTAA）, poly （3,4-ethylenedioxy thiophene）（PEDOT） and theirderivatives or composites. The introduction of surfactants, ionic liquids （ILs）, binders,nanomaterials, or hydrophilic groups, these greatly improved the performance ofenzyme sensors. Especially, ECPs nanocomposites have a good synergisticbioelectrocatalytic effect. Meanwhile, surfactants can improve the water solubility ofmonomers and its polymerization potential (E_ox). ILs can provide a good solventsystem and support electrolytes for water-insoluble monomers. Polymer films basedon binders, can provide a good bio-compatibility and improve the water stability ofpoly （3,4-ethylenedioxythiophene）:polystyrene sulfonate （PEDOT:PSS） films.Ascorbic acid oxidase （AO） can be employed as a mode biomaterial of biologicallyactive species to fabricate enzyme sensors due to its long life span and high and stablebiological activity. More importantly, PEDOT and its excellent functionalizedderivatives or their composite materials can provide excellent immobilized materialsand sensing materials for the immobilization of biologically active species and thefabrication of biosensors.（2） AO biomolecules were selected as the mode biologically active species,PEDOT was employed as immobilized materials of biologically active species, avariety of AO electrochemical biosensors based on PEDOT were fabricated forexploring its application in agricultural fundamental research. The performance ofelectrochemical biosensors and properties of PEDOT can be improved by theintroducation of the biocompatible surfactants, ILs with alkyl sulfate anions, Nafion,carbon nanomaterials, metal nanoparticles, and hydrophilic groups.（a） Theincorporation of the biocompatible surfactants such as sodium N-lauroylsarcosinateand N-dodecyl-β-D-maltoside can improved the solubility and E_oxof monomer3,4-ethylenedioxy-thiophene （EDOT） and the biocompatibility of its polymer films,and the obtained biocompatible PEDOT complex enzyme film is beneficial for thefabricatiom of biosensors and application for to the determination of VC in vegetablecrops and commercial drinks;（b） ILs1-ethyl-3-methyl-imidazol-ethyl sulfate, as agood "green" solvent and supporting electrolyte, can resolve the solubility ofmonomer and improve the efficiency of electron transfer, sensitivity, detection limit,and interference of biosensor;（c） Nafion can improve the stability, biocompatibility,and interference of sensing electrode;（d） nanomaterials such as multi-walled carbonnanotubes, single-walled carbon nanotubes, metal nanoparticles, graphene and itsoxide, not only can improve the electron transfer, bioelectrocatalytic activity of PEODT film, and prevent the leakage of biologically active species, but also enhancethe sensitivity, detection limit, selectivity, stability of sensors;（e） EDOT derivativessuch as the hydroxymethylated EDOT （EDOTM） and functionalized EDOT withcarboxyl group （EDOT-C4-COOH）, which have a good water solubility and a similarE_oxof EDOT, and the obtained polymers not only has a good biocompatibility, butalso available for the immobization of the biological active species by functionalizedgroup;（f） PEDOT:PSS tends to swell and disintegrates in water, the performance ofits film can be improved by incorporation of the adhesive polymers such as Nafion,polyvinyl alcohol, which can also improve stability of biosensors. The improvementof PEDOT:PSS is good candidate for the development and commercialization ofself-made electrode.（3） Various AO electrochemical sensing electrodes based on PEDOT and theirderivatives or composites were fabricated for exploring its application in agriculturalfundamental research. The performance of the electrochemical sensing electrodes canbe improved by introducing carbon nanomaterials, metal nanoparticles, andhydrophilic group. PEDOT nanocomposite sensing electrodes can not only solve theweak electrocatalytic activity and interference of PEDOT sensing electrodes, but alsoimprove sensitivity, detection limit, and stability of electrochemical sensors.Especially, PEDOTM and PEDOT-C4-COOH, as typical representative of excellentPEDOT derivatives, can be copolymerized and composited with other materials, andare also beneficial to the self-assembly of nanoparticles. The fabricatedGCE/PEDOT-C4-COOH/Cu electrochemical sensor can be empolyed for thedetermination of maleic hydrazide in crops and food. The high water-stability ofPEDOT:PSS composites are a promising candidate of electrode materials.（4） Fluorescent chemical sensors based on based on ECPs were fabricated forexploring its application in agricultural fundamental research. A small number ofECPs, which can dissolve in the environment-friendly solvent such as alcohol/water,are excellent sensing materials for the development of "green" fluorescent sensors,and the sensing sensitivity can be enhanced by molecular wire effect of ECPs. Thealcohol soluble fluorescent PBAhas an excellent specific recognition, high sensitivity,and low detection limit for the detection of Pd²⁺, and can be well applied for thedetection of Pd²⁺in samples of agricultural crops or environment. Water-solublefluorescent P9AF can be empolyed for the detection of Fe³⁺and carboxyl compounds,and phosphate can recover the fluorescence quenching of Fe³⁺-P9AF and distinguish determination both of the two analyties. Through the further research, alcohol solublefluorescent PFCAhas an excellent specificity, high sensitivity, and low detection limitfor the detection of Fe³⁺, which is very beneficial for the further application for thedetection of Fe³⁺in agricultural samples.