Study And Application Of CdSe QDs-Based ECL Method Coupled With Molecularly Imprinted Technique For The Analysis Of Chloramphenicol

Electrochemiluminescence（ECL）is a special form of chemiluminescence that is the product of combining electrochemistry with visual luminescence measurements.ECL methods are widely used in many fields because they don’t require an external light source and can perform high S/N measurements with minimal or no background signal with high-sensitivity,rapidity and simple apparatus.Cadmium-based quantum dots（QDs）are composed of IIB and VIA elements,which have wide UV excitation wavelength range,narrow emission wavelength range,high photoluminescence intensity,high photostability and low preparation cost,and have been widely used in the field of optics.In particular,QDs-based ECL analysis has been rapidly developed in recent years.But the poor selectivity seems to obviously restricted the practical application of such methods.Molecular Imprinting Technique（MIT）takes unique advantages for the high-selective identification of targets in a sample.Molecularly imprinted polymers（MIPs）can effectively adsorb target molecules through their specific binding ability between cavities and target molecules and can be synthesized at low cost.Now MIPs have been applied to sensors,drug delivery,sorbents,solid phase extraction（SPE）for sample pretreatments,etc.A QDs-based ECL method based on MIT can further improve the selectivity of an analytical method and facilitate the accurate determination of actual samples.It can be achieved in two ways:one is by preparing MIPs on the surface of QDs for on-line separation and detection,and the other is by preparing molecularly imprinted solid-phase extraction（MISPE）columns with MIPs as fillers for off-line pretreatment of samples.Therefore,in this thesis,a glassy carbon modified electrode was prepared with CdSe QDs as the main body and a ECL sensor was constructed.After the preliminarily investigating the ECL response of the sensor to common antibiotics,a molecularly imprinted polymer film with chloramphenicol（CAP）as the template molecule was prepared on the surface of CdSe QDs（denoted by CdSe QDs@MIPs）.Then the composite was modified on the surface of a glassy carbon electrode to prepare CS/CdSe QDs@MIPs/GCE sensor and the ECL response of the sensor to CAP was investigated.On the other hand,a SPE column was prepared with CAP molecularly imprinted polymer as the filler and its properties were studied;on this basis,a QDs-based ECL method for detecting CAP was established,which helps to realize the high-sensitive and high-selective determination of CAP in honey samples.The proposed strategy provides a method reference for the application of ECL methods to the analysis of antibiotics and other drugs in complex samples.The content of this paper is divided into the following four parts.1 IntroductionFirstly,an introduction to the concept,characteristics,optical properties,preparation methods of cadmium-based quantum dots and their applications in optical analysis is presented.Secondly,the generation and principles of molecular imprinting technique,the preparation methods of MIPs,and the various modes and analytical applications of MISPE technique are briefly described.Thirdly,the QDs-based ECL methods,the related common used systems and their analytical applications are introduced.Finally,the research objectives and contents of this thesis are described.2 Preparation of CdSe QDs and QDs@MIPs and the establishment of their ECL systemsCdSe QDs with mercaptoacetic acid（TGA）as the stabilizer were synthesized by one-pot method,and a glassy carbon modified working electrode（MWCNTs/CdSe QDs/CS/GCE）was prepared with CdSe QDs,multi-walled carbon nanotubes（MWCNTs）and chitosan（CS）as the modification materials.The ECL performance on the as-prepared electrode was then investigated,and the QDs-K₂S₂O₈ cathodic ECL sensor was successfully established to explore its ECL response to different antibiotics.The results showed that CAP had a obvious quenching effect on the ECL of the sensor.In view of this,the CdSe QDs@MIPs material was prepared with CdSe QDs as the core and CAP as the template molecule,and the pathway to improve the selectivity of the QDs-based ECL sensor was initially investigated.3 Preparation,characterization and performance testing of molecularly imprinted solid phase extraction columns for chloramphenicolChloramphenicol molecularly imprinted polymers（CAP-MIPs）were synthesized by precipitation polymerization using CAP as the template molecule,3-aminopropyltriethoxysilanes（APTEs）as the functional monomer,tetraethoxysilanes（TEOS）as the crosslinker and ammonia as the initiator,respectively.Furthermore,a MISPE column was prepared using CAP-MIPs as the filler,and the performance of the MISPE column was investigated.The results showed that the MISPE column possessed good separation capability for CAP by adsorption,and a method for sample pretreatment of CAP-containing specimens was established accordingly.4 Molecularly imprinted solid phase extraction-CdSe QDs ECL method for the analysis of chloramphenicol in honeyAn analytical method for the determination of CAP in honey samples was developed by combining the pretreatment of honey samples with the above MISPE column with the CdSe QDs-K₂S₂O₈ cathodic ECL detection.The experimental conditions such as p H of buffer solution,concentration of K₂S₂O₈,concentration of PBS,low potential value and scan rate were investigated.The results showed that under the optimal conditions,there was a good linear relationship between the logarithmic value of CAP solution and the relative ECL intensity in the concentration range of 1.0×10^-7～1.0×10^-5 mol/L,and the detection limit（3σ）was 1.3×10^-8 mol/L.The relative standard deviation（RSD）was 3.35%（n=6）for six parallel determination of 1.0×10^-6 mol/L standard CAP solution.The present method is simple,rapid and accurate for the spiked recovery determination of CAP residues in honey samples with recoveries ranging from 94.5 to 106.5%.