| Tea polyphenols are the generic term of polyphenol compounds in tea,which have strong antioxidant activity can eliminate harmful free radicals,widely used in food preservation,antibacterial,healthcare and other fields.Tea polyphenols are the main functional component having an important impact on the quality of tea and its products,so the determination of tea polyphenols is an effective method for the quality identification of tea and its products.At present,the detection methods of tea polyphenols include chromatography,mass spectrometry,spectrophotometry,and near-infrared spectroscopy,etc.,but there are some problems such as slow speed,low integration,and high costs in these detection methods.Therefore,it is worth further research to establish a fast,accurate and low-cost detection method of tea polyphenols.For solving above problems,this thesis proposes a novel detection method of tea polyphenols based on microfluidic chip and electrochemical technology with a combination of the technical advantages of microfluidic chip and electrochemical detection.Then it was applied to the determination of total tea polyphenols in Pu-erh tea samples.The research contents and conclusions of this thesis are as follows:?1?The electrochemical detection principle of tea polyphenols and mixing mechanism of the microfluidic chip were studied.Firstly,the theoretical equation of cyclic voltammetry was studied based on the theory of electrochemical detection,which found that the oxidation peak current of cyclic voltammetry curve is proportional to the concentration of reactants.Then,the electrochemical reaction mechanism of tea polyphenols was analyzed,expounding the principle and feasibility of cyclic voltammetry detection for tea polyphenols,and the gallic acid was chosen as standard substance.Finally,the mixing mechanism of microfluidic chip was explained based on the theory of fluids mixing,which laid a theoretical foundation for the structural design of the microfluidic chip and the optimization by flow field simulation.?2?The optimal design of structure in the microfluidic chip was carried out by COMSOL flow field simulation analysis.Firstly,according to the requirements of the electrochemical detection of tea polyphenols,a microfluidic chip integrated with the function of fluids mixing and cyclic voltammetry detection was designed.Then,the flow field simulation analysis of the mixing process was performed through COMSOL software to investigate the distribution characteristics of the flow field in the mixing flow passages,revealing the mechanism of intensifying mixing process by ribs.Finally,the effects of five key parameters such as inlet Reynolds number,rib shape,rib size,entrance angle and mixing distance on the mixing performance of the microfluidic chip were ascertained,and the structure parameters of the mixing flow passage were also optimized,which obtained a microfluidic chip with good mixing uniformity and low pressure drop.?3?The DLP 3D printing technology was applied to fabricate the microfluidic chip,and a microfluidic chip electrochemical detection platform was established.Firstly,according to the requirements of rapid and low-cost manufacturing of the microfluidic chip,the manufacturing process was analyzed,and the advantages and disadvantages of different 3D printing technologies were expounded.The DLP technology was found to print quickly with high resolution,chosen to print the microfluidic chip at last.Then,the surface of the microfluidic chip was treated with the piranha solution,which can avoid the generation and enrichment of air bubbles in the microfluidic channels.Finally,the microfluidic chip was packaged with hot-melt adhesives and the microfluidic chip electrochemical detection platform was constructed successfully.?4?The experimental researches on determination of total tea polyphenols were carried out using the microfluidic chip electrochemical detection platform.Detection parameters of tea polyphenols were optimized by single factor experiments,which obtained the optimal cyclic voltammetry curve under the conditions of the B-R buffer at p H 3.0,the scanning speed of 100 mV/s and the feeding speed of 40?L/min.Under the best detection conditions,a good linear response was found at the concentration of gallic acid ranging from 5 to 1250?mol/L,and the limit of detection is 6.9×10-7 mol/L.The detection results of Pu-erh samples showed that the recovery rates of the samples range from 97.6%to 104.6%,and the deviation from the result of the Folin-Ciocalteu method is about 5.5%.The testing time is less than 1 min,and the amount of samples and reagents is reduced to microlitres.This thesis proposes a detection method of tea polyphenols based on microfluidic chip and electrochemical technology,and it is practical verified by carrying out the theoretical researches,flow field simulations and experiments.This method has important value for the rapid,accurate,low-cost detection of total tea polyphenols,and it can also be popularized and applied to the rapid detection of other food compositions. |
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