Study Of Sensor Coatings Based On Complex-assembly Of Modified Poly(γ-glutamic Acid)

Macromolecular self-assembly as one of the hot topics of polymer science has drawn significant attentions in the last decade. Scientists systematically and deeply studied the mechanism of macromolecular self-assembly process and obtained remarkable achievements. With the development of the research on macromolecular self-assembly, the building blocks and process of assembly are getting more complex. In addition, the complex assembly of multicomponenthas been developed to fabricate functional aggregates. Numbers of complex aggregates, which have special structure and function, have been prepared by the controllable assembly process induced by fields. The self-assembly of molecules or molecular aggregates have created a new method for fabricating new materials. It is expected that besides the chemical synthesis, the self-assembly would create more diversity of new multi-scale material and new functional materials and new functional device for humans.In our previous work, we investigated the hierarchical assembly of amphiphilic copolymer at the interface of liquid-liquid. The results indicated that the nanoparticles self-assembled from amphiphilic random copolymer can be used to stabilize Pickering emulsion. In addition, we combined the advantages of amphiphilic copolymer self-assembly, molecular imprinting with those of electrodeposition and developed a novel molecularly imprinted polymeric nanoparticles(MINPs) based voltammetric sensor. However, the method of using photo-crosslinkable MINPs and electrophoretic deposition to prepare sensor coatings was only focused on synthetic polymer, which greatly limits its application.Poly(γ-glutamic acid)(γ-PGA) is a microorganism metabolite produced by some Bacillus species, consisting of γ-carboxylinked glutamate residues. With excellent biodegradability, biocompatibility, moisture-retention and environmentally friendly, γ-PGA has been widely used in the fields of food, medicine, agriculture, environmental protection and cosmetic. The applications of self-assembled γ-PGA-based nanoparticles are mainly focused on the immunity and the delivery of proteins and drugs.In this thesis, we used modified poly(γ-glutamic acid) copolymer and functional elements as the multi-component building blocks of assembly to prepare complex aggregates. The resultant aggregates were then electrodeposited on the surface of electrode using electrophoretic deposition technique, obtaining an aggregates coating. We aimed to investigate the process of hierarchical assembly of modified γ-PGA copolymer, and develope the practical application in the field of sensor coating based on complex-assembly of modified poly(γ-glutamic acid).The work in this dissertation includes the following parts:1. Study of molecularly imprinted sensor coating based on hemoglobin/poly(γ-glutamic acid) nanoparticles7-amino-4-methylcoumarin was used to modify γ-PGA to obtain novel photo-sensitive amphiphilic 7-amino-4-methylcoumarin modified poly(γ-glutamic acid)(γ-PGA-AMC) copolymer, which was then used to complex with hemoglobin(Hb), forming the Hb/γ-PGA-AMC molecularly imprinted nanoparticles(MINPs). The resultant MINPs were then placed on a glassy carbon electrode via electrophoretic deposition. Subsequent photo-crosslinking locks the recognition sites. The template was removed by extraction with a mixture of acetic acid and methanol at a ratio of 1:9(V:V), to obtain a voltammetric sensor coating for Hb. The results indicated that the photo-sensitive amphiphilic γ-PGA-AMC copolymer can be successfully used to imprint Hb. The sensor coating prepared from Hb/γ-PGA-AMC MINPs via electrophoretic deposition can be used to directly detect Hb in aqueous solution. The method of preparing sensor coating combining the macromolecular self-assembly technology and electrophoretic deposition technology had been expanded to the field of biological macromolecules.2. Study of sensor coating based on Au/poly(γ-glutamic acid) nanohybridsDopamine was used to modify γ-PGA, obtaining dopamine modified γ-PGA(γ-PGA-DA) copolymer through amidation reaction. By simply adding HAu Cl4 to the aqueous solution of γ-PGA-DA copolymer, Au/γ-PGA-DA nanohybrids were formed. The complex-assembly of nanohybrids and the sensing properties based on nanohybrids coating were then investigated. The results indicated that the electrical conductivity and detection sensitivity of the nanoparticles coating can be greatly improved due to the introduction of the Au nanoparticles; The structure and the sensing property of Au/γ-PGA-DA nanohybrids varied with the loadings of HAu Cl4 and the p H value; The particle size and clustering of Au NPs can influence the sensing properties of Au/γ-PGA-DA nanohybrids coating for L-tryptophan; With the decrease of Au NPs size and the enhancement of dispersion of Au NPs in Au/γ-PGA-DA nanohybrids, the electrical conductivity and detection sensitivity of Au/γ-PGA-DA nanohybrids coating increased.3. Study of sensor coating based on Au/poly(γ-glutamic acid) nanohybrids via electrophoretic depositionA sensor coating based on Au/poly(γ-glutamic acid) nanohybrids was prepared for L-tryptophan sensing via electrophoretic deposition. The effects of deposition condition for the structure and property of coating were investigated. The results indicated that the morphology and the sensing property of Au/γ-PGA-DA coating were controllable through changing the deposition condition. The Au/γ-PGA-DA nanohybrids can be deposited more quickly when greater applied fields were used. The more uniform coatings were deposited at lower applied fields, whereas the coating quality deteriorates if relatively higher applied fields were used. With decreasing the size of Au/γ-PGA-DA nanohybrids in aqueous solution via altering the Na Cl concentration and p H value, the sensing property of Au/γ-PGA-DA nanohybrids coating increased. The deposition was linear during the initial time of deposition process. But as more and more time was allowed, the deposition rate decreased and attained a plateau at very high deposition times. At the time of formation of the uniform coating, the Au/γ-PGA-DA nanohybrids coating responded linearly to L-tryptophan with the widest range.4. Study of molecularly imprinted sensor coating based on Ag/melamine/poly(γ-glutamic acid) nanohybridsThe γ-PGA-DA copolymer was converted into NPs that were imprinted with melamine(MEL). By simply adding Ag NO3 to the aqueous solution of MEL/γ-PGA-DA MINPs, Ag/MEL/γ-PGA-DA MINPs were formed. After Ag/MEL/γ-PGA-DA MINPs were placed on a gold electrode, the template was removed by electrolysis, to obtain a voltammetric sensor coating for MEL. The results indicated that the electrical conductivity and detection sensitivity of the sensor coating detecting for MEL can be greatly improved due to the introduction of the Ag nanoparticles. The structure and property of the Ag/MEL/γ-PGA-DA MINPs varied with the concentration ratio of building blocks and the p H value of solution. With the the enhancement of dispersion of Ag NPs and MEL in MINPs, the sensing property of MINPs coating increased.In this thesis, we used modified γ-PGA copolymer and functional elements as the multi-component units of assembly to prepare complex nanoparticles via weak interactions. The resultant complex nanoparticles were then electrodeposited on the surface of electrode using constant voltage method to obtain a nanoparticles coating. The application of γ-PGA-based complex nanoparticles was expandeded to sensor coating. Furthermore, the relationship of the condition of the hierarchical assembly and the properties of sensor coating had been systematically investigated.