Preparation Of Highly Sensitive Cr₂O₇^2- Fluorescent Sensors Based On Polyfluorene And Their Application In Agriculture

Hexavalent chromium（Cr（VI））is a common heavy metal pollutant and carcinogen.In general,it is usually enriched in industrial wastewater or natural water in the form of dichromate ions(Cr₂O₇^2-).Long-term intakes of Cr₂O₇^2-may lead to DNA damage,lung adenocarcinoma,respiratory system damage or genetic defects.Cr₂O₇^2-can also be transmitted through the food chain,directly or indirectly endangering human health and causing lasting damage to the environment.In particular,Cr（VI）pollution in farmland will directly affect the quality and safety of agricultural products and food.Therefore,in order to treat the pollution of Cr₂O₇^2-effectively,it is extremely urgent and valuable to construct a fast detection and specific identification of the Cr₂O₇^2-fluorescence sensor.Compared with the current fluorescent materials for the detection of Cr₂O₇^2-,conjugated polymers（CPs）have a strong light-harvesting ability and molecular wire properties,which can realize the amplification of hundreds or thousands of fluorescent response signals.Thus,it stands out in the fields of biological detection（metal ion/anion detection,biomolecular sensing,bioimaging）and environmental analysis（explosives detection）.The development and preparation of CPs fluorescent sensor materials with high sensitivity,strong selectivity and high accuracy has become one of the research hotspots in analysis and testing.However,there are few reports on the specific recognition of Cr₂O₇^2-fluorescence sensors based on CP fluorescent materials,and there is no clear strategy to guide the design of such sensors.Based on the current research foundation,CPs-based fluorescence sensors with high selectivity,high sensitivity and low detection limit were constructed via grafting fluorene with four different functional side chain groups for the detection of Cr₂O₇^2-,and they were successfully applied to detect practical samples in this thesis.1.Two monomers,9-fluorenemethoxycarbonylarginine and 9-fluorenemethoxycarbonylglutamic acid,were polymerized by electrochemical method to obtain their polymers,respectively.The fluorescent sensors prepared by two polymers could realize the highly selective detection of Cr₂O₇^2-.Two water-soluble polyfluorene derivatives P（Fmoc-Arg-OH）and P（Fmoc-Glu-OH）were synthesized using electrochemical polymerization in boron trifluoride diethyl etherate-trifluoroacetic systems.The polymerization of fluorene was at positions 2 and 7,which was confirmed by ¹H NMR spectra,and the absorption and emission spectra indicated that two polymers were blue emitters.A series of selective and competitive experiments in p H=7.00 PBS solution showed that they had high selectivity towards to Cr₂O₇^2-.Thanks to the signals amplification effect,the limit of detections（LODs）of P（Fmoc-Arg-OH）and P（Fmoc-Glu-OH）could reach 16.67 p M and 3.33μM,respectively.All results displayed that CPs are a good platform for designing fluorescent sensors with high selectivity and sensitivity.2.Aminobutyric acid-functionalized polyfluorene enables the trace detection of Cr₂O₇^2-,which provides the possibility to develop Cr₂O₇^2-fluorescent sensors with higher sensitivity.A conjugated polymer fluorescent material（P（Fmoc-GABA-OH））was prepared by electropolymerization of fluorene grafted with aminobutyric acid.The fluorescence sensor prepared by the polymer has good water solubility and fluorescence properties,such as high selectivity and strong anti-interference ability.Using this sensor,the detection of Cr₂O₇^2-was achieved via a fluorescence-quenching mechanism with a LOD of 16.6 f M.This approach could be applied for monitoring the Cr₂O₇^2-concentrations in farmland water,soil,tangerine,orange,and grapefruit samples.The present finding will not only extend the scope of CP-based sensors but also provide a new strategy for the ultra-trace detection of Cr₂O₇^2-.3.The Cr₂O₇^2-fluorescence sensor with high selectivity,strong anti-interference ability and ultra-trace detection ability was also prepared by selecting rigid side chains of succinimide carbonate containing N and O atoms in fluorene.The monomer Fmoc-Osu was electropolymerized in the boron trifluoride diethyl etherate solution to obtain the conjugated polymer P（Fmoc-Osu）.The results show that the selectivity of P（Fmoc-Osu）for Cr₂O₇^2-is higher than that of 15 common anions and22 cations,and the detection limit is 8.3 f M,which can realize the trace analysis of Cr₂O₇^2-.Transmission Electron Microscope demonstrated that Cr₂O₇^2-interacted with the polymer to cause aggregation between polymer chains,resulting in fluorescence quenching.Finally,it was successfully applied in the detection of Cr₂O₇^2-in farmland vegetable samples,which solved the problem of ultra-trace detection of Cr₂O₇^2-in complex environmental samples and at present it is a fluorescence sensor with the lowest detection limit for Cr₂O₇^2-.All these results showed that P（Fmoc-Osu）is an efficient tool to detect Cr₂O₇^2-in practical applications.