| Benzimidazoles(BMZs)pesticides are the most widely used systematic fungicides in agricultural production,making them one of the most detected and maximum residual pesticides in the production of fruits and vegetables.Currently,gas chromatography-mass spectrometry(GC-MS)has become the main mean of detecting BMZs residues.Although the instrumental detection techniques of BMZs residue present good results,these techniques are complicated,cumbersome pre-treatment,expensive equipment,time-consuming,require high instrument operators,and cannot present the status of BMZs residue in real-time,and have time lag for ensuring the safety of fruit consumption.Fluorescent colorimetry is an important component of spectroscopic detection due to its excellent detection properties.The rapid development of nanotechnology has provided a wide scope for fluorescent detection.Carbon Dots(CDs),an organic Quantum Dots(QDs),have been used in the fluorescence detection of food nutritional functional components and hazards.However,the complexity of the food system strongly interferes with the stability of the CDs signal,and the sensitivity and selectivity of the detection have posed serious challenges.In order to improve the performance of the sensor,ratiometric fluorescence has been introduced into the analysis field.The ratiometric fluorescence sensor(RFS)based on various hybrid nanocomposites can reduce the interferences in the complex detection system by signal separation and signal overlap.It is one of the effective ways to improve the sensitivity and selectivity of CDs sensor.Therefore,this study focused on the design of CDs-based ratiometric fluorescence sensors for the detection of BMZs residues,including carbendazim(MBC)and thiophanate-methyl(TM).The selected CDs are used to construct CDs-based ratiometric fluorescence sensors and the recognition mechanism and anti-interference mechanism of the sensors were explored in food matrices,providing a scientific basis for the wide application of CDs in food detection for ensuring food safety of fruits and vegetables.The specific work includes the following aspects.1.Based on the molecular properties of BMZs pesticides,several functionalized CDs,such as triethylenetetramine modified CDs(TETA-CDs),copper-doped triethylenetetramine modified CDs(TETA-CDs/Cu),cysteine-modified CDs(Cys-CDs),1-(2-pyridylazo)-2-naphthol CDs(PAN-CDs),5-aminoisophthalic acid(AA-CDs),and diphenylaminourea-modified CDs(SD-CDs),were prepared using one-pot hydrothermal method(180°C,2-4 h)with citric acid as the carbon source.The characterization of CDs and the investigation of the binding performance of CDs with BMZs molecules were carried out to evaluate the fluorescence response between different CDs and BMZs.The results showed that the obtained CDs with aromatic ring ligands(PAN-CDs)possessed significant fluorescence response to MBC and TM to provide a basis for the construction of the sensor.2.Copper ions(Cu2+)triggered carbon dots(CDs/Cu)with dual emissions were utilized to develop a ratiometric fluorescence sensor for ultrasensitive detecting inert thiophanate-methyl(TM).The Cu2+-excited dual-emission fluorescent carbon dots(CDs/Cu)were prepared by a one-pot hydrothermal method based on the fluorescence-responsive single-emission CDs prepared in Chapter 1 with the addition of Cu2+to construct a ratiometric fluorescence sensor.The fluorescence ratio of CDs/Cu(F416/F481)linearly responded in the TM concentration of 0.10-20.00?mol/L with an ultralow limit of detection of 2.90×10-6?mol/L.The synchronous response of the ratiometric sensor enhanced the specificity toward TM and presented a remarkable capability of anti-interference in complex matrices.The sensor exhibited satisfactory accuracy and precision for practical applications with recoveries of 88.33-101.09%and RSDs of 1.61-5.06%,demonstrating an ultrasensitive ratiometric fluorescent nanosensor for detecting pesticides residues in complex matrices.The mechanism of detection showed that TM could be recognized by CDs/Cu through?-?stacking and chelated the Cu2+of CDs/Cu through metal ion coordination,causing excited-state intramolecular proton transfer(ESIPT)and ligand-to-metal(LTM)to enhance the selective detection of TM.3.Terbium(III)referenced carbon dots(PAN-CDs&DPA-Tb)with dual emissions were utilized to develop a ratiometric fluorescence sensor for sensitive detecting carbendazim(MBC)in the food sample.The ratiometric signal of the sensor(F363/F544)linearly responded to the concentrations of MBC in 0-0.091 mmol/L with a limit of detection(LOD)of 3.0×10-3?mol/L.The considerable selectivity of the sensor toward MBC and the remarkable capability of anti-interference in complex matrices were observed due to the synchronous response of the ratiometric sensor.The sensor exhibited satisfactory accuracy and precision for practical applications with recoveries of 92.22-106.08%and RSDs of 0.14-1.69%,demonstrating a high-sensitive and selective ratiometric fluorescent sensor for detecting pesticide residues in complex matrices.4.A ratiometric fluorescent sensor for the high-sensitive and-selective detection of inert MBC in fruits and vegetables was facilely fabricated using innate fluorescence of pesticide carbendazim(MBC)and Ui O-67.Multi-emission fluorescence for ratiometric fluorescence sensor construction by simple proportional mixing the fluorescence response single-emission CDs from the first chapter and DPA-sensitized Tb3+fluorescence to obtain a ratiometric fluorescent sensor to MBC.The fluorescence ratio(F311/F408)linearly responded to the MBC concentrations of 0-47.6?mol/L with a low limit of detection(LOD)of 3.0×10-3?mol/L.The reverse response signals of the sensor enhanced the sensitivity toward MBC and presented remarkable anti-interference capability in complex matrices.Finally,the sensor was evaluated on detecting MBC in real samples obtaining satisfactory accuracy and precision with the recovery of 90.82-103.45%and RSDs lower than 3.03%.The fluorescence enhancement of MBC(F311)and the quenching of Ui O-67(F408)were observed in the increasing concentrations of MBC.The innate fluorescence of MBC provided a steady fluorescent signal,while MBC could be recognized by Ui O-67 through?-?stacking inducing fluorescent quenching relied on photoelectron transfer(PET)providing another fluorescent signal.in addition,inter filtration effection of MBC showed a strong specificity of the detection.The reverse response of the dual-emission fluorescence of this sensing system enhanced the selectivity and anti-interference ability of the sensor for MBC.All of the three detection methods could fulfill the sensitivity required by national and international standards,and different sensors showed different sensitivity and selectivity to MBC and TM.The copper ion(Cu2+)excited CDs ratiometric fluorescence sensor exhibits a higher detection sensitivity for TM with a LOD value of 2.90×10-6?mol/L,but the sensor poses a narrow detection range and is suitable for the detection of TM residues at very low concentrations.Terbium(Tb3+)reference CDs ratiometric fluorescence sensor and MBC coupled Ui O-67 ratiometric fluorescence sensor have the advantages of being simple and easy to implement,showing excellent selective detection for MBC,better than the detection limits of existing detection methods while having a larger detection concentration range,suitable for rapid detection of MBC under conventional conditions.In addition,because TM is easily converted into MBC,in practical applications,the significance of detection of MBC by Terbium(Tb3+)reference CDs ratiometric fluorescence sensor and MBC coupled Ui O-67 ratiometric fluorescence sensor is much higher than the detection purpose of TM by copper ion(Cu2+)excited CDs ratiometric fluorescence sensor,therefore,this quantum sensor is more realistic to utilize. |
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