Studies Of The Jasmonates Electrochemical Sensor Based On Graphene Nanomaterials

Plant hormones are a kind of signaling molecules with biological activity, which can be synthesized in the plants, transport among different tissues and take effect in specific parts. Their concentrations are very low in plants. They can promote growth, facilitate rhizogenesis, inhibit germination during storage, break dormancy, prevent desquamation, control bolting and flowering, control sex, accelerate ripening and early harvest, preserve verdure during storage, weed through chemical method, produce seedless fruits, etc. Plant hormones participate in a variety of adjustment processes of physiological activities, and play a key role throughout the whole growth cycle of the plants. Therefore, the development of analysis methods for the plant hormones in plant organizations is of great significance for studying their physiological effects and the regulation of agricultural production. Among the multitudinous means of detection, electrochemical method has been paid much attention because of its easy operation, cheap equipment, fast response, high sensitivity and no need for complicated sample pretreatment process. However, the electrochemical activities of plant hormone are weak, so the design of electrochemical sensor system with strong catalytic ability and high sensitive interface for plant hormone is the main challenge of current research.There is ion exchange capacity between the layers of nano-layered compounds, so guest molecules or ions can be introduced into their layers through various intercalation techniques, and the properties of the nano-layered compounds can be improved. The intercalated nano-layered compounds have both the properties of host and guest molecules, which can exhibit adsorption, catalytic and electric ability that the single molecules can not own, and therefore have potential applications in many areas including fabrication of chemical or biological sensors, molecular recognition, catalysis, and so on. In addition, the heteropoly compounds have high stability and adjustable redox potentials, which can be used as redox catalysts in the electrochemical processes of many substances with weak electrochemical activities. The excellent properties of these materials were utilized synthetically here for the fabrication of plant hormones electrochemcal sensors. The electrochemical behaviors of plant hormones were investigated and the applications of these senors in plant samples were also studied. The main contents of this thesis include:(1) The nano-montmorillonite (nano-MMT) colloidal film with high stability in water was synthesized and modified on the surface of glassy carbon electrode through simple dipping-drying method. Then a novel methyl jasmonate (MeJA) sensor was fabricated. The electrochemical oxidation behaviors of MeJA were studied, based on which a detection method was developed by using the first derivative square wave voltammetry. This sensor could be used to determine MeJA in rice spikelet with results which are consistent with that from high performance liquid chromatography (HPLC) method.(2) Based on the ion exchange ability of montmorillonite (MMT), protonated neutral red (NR) was intercalated into the layers of MMT, which had expanded the interlayer space of MMT and therefore promoted the accumulation effect of MMT for bigger molecules. Through electrostatic attraction, NR-MMT and phosphotungstic acid (PTA) with rich negative charges could be self-assembled onto the surface of graphite electrode for the fabrication of methyl jasmonate (MeJA) electrochemical sensor. This sensor showed strong catalytic ability for the determination of MeJA with a wide linear range and a low detection limit, when applied for the determination of MeJA in rice spikelet, the results and that from HPLC method are accordant.(3) There are abundant negative-charged oxygen-containing groups on the basal layers and edges of graphene oxide (GO), so alkylamines could be intercalated into the layers of GO through simple chemical reaction. The prepared alkylamines-GO nanohybrid and phosphotungstic acid (PTA) layer-by-layer self-assembling fim exhibited very strong catalytic effect for the oxidation of methyl jasmonate (MeJA). And it was deduced that the oxidation occurred on the alkene of MeJA. This study has not only opened up a new way for the electrochemical determination of alkene-based compounds, but also expanded the application of graphene and its composites in the fabrication of electrochemical sensors.(4) The graphene-polymeric dye nanocomposite was for the first time synthesized and then applied for the fabrication of auxin indole-3-acetic acid (IAA) electrochemical sensor. After graphene (rGO) was self-adsorbed onto the surface of graphite electrode (GE), a very thin poly(safranine T) (PST) film was then formed through simple and controllable electropolymerization mthod. This IAA sensor has improved the detection sensitivity of IAA significantly and could be applied to determine IAA content in the leaves of Cinnamomum camphora, Prunus yedoensis Mats. and Firmiana simplex successfully, which has been verified by HPLC method. Simultaneously, the electrochemical oxidation mechanism of IAA at this sensor was investigated.(5) Through simple grinding, fullerene-graphene oxide (C60-GO and C70-GO) composites based on p-stacking were prepared. They could be dispersed into water with the aid of abundant hydrophilic groups on GO. A series of methods were used to characterize the combination of fullerene and GO. When mixing the fullerene-GO composite with phosphotungstic acid (PTA), PTA-fullerene-GO composites modified glassy carbon electrode could be prepared through one-step electrodeposition. Some small biomolecules, including dopamine, ascorbic acid, uric acid, L-tryptophan, tyrosine, indole-3-acetic acid, salicylic acid and 6-benzylaminopurine were selected as electrochemical probes to study the electrochemical catalytic mechanism of this modified electrode.(6) The above PTA-C60-GO nanocomposite was electrodeposited simultaneously on the pre-anodized and pre-cathodized graphite electrode (GE), based on which a novel cis-jasmone (CJ) electrochemical sensor was developed. The anodized and cathodized pretreatment processes had made the graphite sheets on GE surface become smaller and tend to more nanometer-scaled, could remove the amorphous impurities and make the surface of electrode smoother, so the enhanced electrochemical response of CJ could be obtained. After further electrodeposited by PTA-C60-GO nanocomposite, the oxidation peak current of CJ increased and the peak potential negaive-shifted significantly. This CJ electrochemical sensor could be used to determine CJ in rice spikelet with satisfying results, which had been compred with the results from HPLC method.