The Fabrication Of Functionalized Mesoporous Materials Enhanced Molecularly Imprinted Nano-Composite System And The Study On Specific Detection Of Alkaloids

Alkaloids with natural physiological activities are the active components of many medicinal plants and Chinese herbal medicines.However,some toxic alkaloids can cause diseases and pose serious injury or even death to human beings.Therefore,it is necessary to establish a simple and efficient analytical method for the accurate determination of alkaloids.The composition of plants is very complex and the content of alkaloids in them is relatively low,so the detection of alkaloids in biological systems with high sensitivity and specificity has become a technical problem that is urgently needed to be solved.Molecularimprintingtechniquesimulatestherecognitionmechanismof antigen-antibody and adopts chemical methods to synthesize molecular imprinted polymer?MIP?.The MIP with the merits of good stability,high selectivity,big adsorption capacity and long life-time has specific recognition effect for target substances both from binding sites and spatial structure.MIP can be used as specific recognition element for electrochemical sensors,which opens a new way for selective detection of trace alkaloids.In recent years,the introduction of functionalized nanomaterials?porous materials,metal nanoparticles?provides more recognition sites for MIP,and the excellent catalytic and conductive properties of nanomaterials are more favorable for electron transport.Therefore,the sensitivity and specificity of the molecularly imprinted electrochemical sensor can be enhanced significantly.Based on this,four kinds of MIP were prepared by bulk polymerization and surface imprinting,and were used for the electrochemical sensing of theophylline,atropine and theobromine respectively.The main contents and results are as follows:1.This work is focused on a typical core-shell structured Si O₂@TiO₂-based imprinted polymer composite,employed as a molecular recognition and sensing interface in the construction of an innovative electrochemical sensor.Herein,the methacrylic acid and a bronchodilator drug,theophylline,were used as functional monomer and template,respectively.The Si O₂@TiO₂ served as a potential signal transducer to shuttle electrons between the binding sites and the electrode.Such modification induced an electrocatalytic effect and thereby greatly improved the electrode kinetics.The analytical features of the developed theophylline sensor have been accessed,and the results have indicated that an increase of differential pulse voltammetric current as compared to the corresponding traditional imprinted polymer modified electrode.Moreover,the sensor has showed high sensitivity,wider linear range was 0.01-40?mol/L,lower detection limit was 1.2 nmol/L,which was validated with the complex matrices of tea,human blood serum,and urine.2.In order to solve the problems of tedious post-processing method and low yield of MIP obtained by bulk polymerization,the study of fabrication of theophylline molecularly imprinted electrochemical sensing system based on surface imprinting technology was carried out.Here,we report a three-dimensional network MIP on electrode surface to achieve an efficient and specific detection of theophylline in foodstuffs,using theophylline as the template molecule,mesoporous silica nanospheres?MSNs?as the signal transducer to shuttle electrons,and both phenyltriethoxysilane and pyrrole as functional monomers.The electron microscope images revealed the presence of well-distributed hierarchically MSNs with a pomegranate-like morphology,topped with MIP uniform layer.Electrochemical characterizations were carried out to monitor the properties of the resulting sensing platform based on the MIP/gate effect employing hexacyanoferrate molecules as the electrochemical probe.The data showed that due to the high conductivity and electron transfer ability of the prepared theophylline-imprinted membrane,this method exhibited excellent sensitivity and binding affinity with a linear dynamic concentration range in excess of six orders of magnitude?0.005-1000?mol/L?and low detection limit?0.66 nmol/L?,meeting the requirements of theophylline trace analysis.3.The metal-organic frame materials have the characteristics of high specific surface area and porosity,low density,uniform and adjustable pore size and chemical functionalization.In this work,Zeolitic Imidazolate Framework?ZIF?was uniformly grown on the surface of MSNs to prepare a novel flower-like MSNs@ZIF-8 core-shell material,which was modified on the electrode surface for electrochemical deposition of Au nanoparticles.Then,the 5-amino-2-mercapto-1,3,4-thiadiazole functional monomers and atropine template molecules were assembled on the surface of modified electrode by Au-S bond and hydrogen bond interaction,and the surface imprinted polymer was prepared by electropolymerization.The preparation conditions including polymerization system,the amount of template molecules and functional monomers,elution time,adsorption time and pH value were optimized through cyclic voltammetry and differential pulse voltammetry.Under the optimal conditions,the linear range for atropine detection on this sensor was 0.05-95?mol/L,and the detection limit was 10nmol/L.In the detection process of grain and biological samples,the recovery was between 94.3-106%,which indicated that the sensor could be used for rapid and accurate detection of atropine in real samples.4.In order to further improve the conductivity of porous materials,the Au nanorod was encapsulated completely into the Ag shell with a thickness of about 8.5 nm,and then the mesoporous silicon was further deposited on the surface of this alloy to prepare three core-shell structured AuNR@Ag@mSiO₂ composite.Afterwards,an electrochemical sensor with specific recognition ability for theobromine using sol-gel method was prepared with AuNR@Ag@mSiO₂ as the sensitizer,theobromine as the template molecules,3-aminopropyltriethoxysilane as the functional monomers,and tetraethyl orthosilicate as the cross-linking agent.Due to the doping of AuNR@Ag@mSiO₂,the detection sensitivity and accuracy for theobromine on this molecularly imprinted membrane sensor were improved obviously.The linear range was 0.01-100?mol/L and the detection limit was 8 nmol/L.At the same time,the sensor had high stability and good reproducibility.When applied in the analysis of tea,coffee and biological samples,the relative standard deviation was less than 3%,and the recovery was between92.9-107%,indicating the high practical application value of this sensor.