Preparation Of Gold Nanoparticles @Cellulosic Micelles And Their Application In SERS Detection For Methylene Blue

As a reliable and sensitive detection method,surface enhanced Raman scattering?SERS?has been widely used in various fields such as biological diagnosis,environmental monitoring,chemical sensing and food quality.Gold nanoparticles?Au NPs?are excellent SERS substrates due to their unique physicochemical properties,especially the characteristics of localized surface plasmon resonance.In this work,amphiphilic cellulosic micelles were prepared from cellulose through the thiol-ene click reactions and self-assembly in aqueous solutions;cellulosic micelles were further served as templates for preparing Au NPs through the photo-reduction;Moreover,Au NPs loaded micelles were used as the SERS substrates to sensitively detection of methylene blue?MB?.The novel creations of this work are as follows:1)A series of amphiphilic cellulosic micelles with the controlled size were obtained by changing the degree of substitution of n-dodecyl mercaptan(DS_NDM)and the molecular weight of cellulose;2)The size-tunable Au NPs were prepared by using the cellulosic micelles as the soft templates,and the photo-reduction mechanism was clarified;3)The SERS activity of Au NPs loaded micelles was investigated,and their application as SERS substrates for sensitively MB detection was proved.The main contents and conclusions of this thesis are as follows:Allyl cellulose?AC?derivatives with a DS of 0.98 were synthesized by the reaction of three kinds of cellulose with a viscosity average molecular weight?M??of30,70 and 130 k Da with allyl chloride in Na OH/urea aqueous solution.Amphiphilic cellulose derivatives?AC-Cys-NDMs?were synthesized by AC,cysteine and dodecyl mercaptan via thiol-ene click reactions.AC-Cys-NDMs were self-assembled in water,and the morphology and size of the obtained micelles were characterized by using dynamic light scattering?DLS?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?and atomic force microscopy?AFM?.The results showed that cellulosic micelles had a narrow size distribution and uniform dispersed in water.As the DS_NDM increased from 0 to 0.15,the size of the micelles increased.The hydrodynamic radius?R_h?of 3-MC-0?3,7-MC-0?3 and 13-MC-0?3 increased from106 to 147 nm,110 to 158 nm and 125 to 166 nm,respectively.The R_h values of cellulosic micelles slightly increased with an increase of the M?of cellulose.TEM measurements further proved that the cellulosic micelles have uniform size distribution,and the size of 13-MC-0?3 increased from 36 to 45 nm with an increase of DS_NDM from 0 to 0.15.Au@MC composite micelles were prepared though photo-reduction using amphiphilic cellulosic micelles as reducing and protective agents.The photo-reduction mechanism,the morphology and size of the Au NPs loaded micelles,and factors affecting the size of Au NPs were characterized by using IR,DLS,TEM,SEM,AFM and X-ray photoelectron spectrometer?XPS?.The results indicated that the-NH₂ groups on the amphiphilic cellulose derivative reduced HAu Cl₄ to Au NPs.The hydrophobic core and the strong interaction between Au and S atoms stabilized and enclosed the Au NPs inside the cellulosic micelles.As the DS_NDM increases from 0 to0.15,the R_h values of Au-loaded micelles increased,and the size of Au NPs also gradually increased.The R_h values of Au@3-MC-0?3,Au@7-MC-0?3 and Au@13-MC-0?3 increased from 161 to 219 nm,159 to 219 nm and 133 to 219 nm,respectively.Correspondingly,the size of Au NPs increased from 7.0 to 8.9 nm,7.3 to8.9 nm and 7.5 to 10.4 nm,respectively.The sizes of Au-loaded micelles increased with an increase in the concentration of the cellulosic micelles and a decrease in the concentration of HAu Cl₄,while the M?of cellulose had little effect on the size of the synthesized Au NPs.Au-loaded micelles were used as the SERS substrate for Raman detection of MB.The size of Au NPs and the volume of Au@MC would significantly affect the SERS signal strength of MB,while the size of cellulosic micelles had little effect on SERS signal.The peak intensity at 1626 cm^-1 collected with Au@13-MC-1(d _Au=8.3 nm)was about 2.2,3.9 and 5.9 times of those acquired with Au@13-MC-0(d _Au=7.5 nm),Au@13-MC-2(d _Au=9.2 nm)and Au@13-MC-3(d _Au=10.4 nm),respectively.When the volume of Au@13-MC-1 aqueous solution increased from 20 to 80?L,the peak intensity at 1626 cm^-1 increased by 2.2 times.The LOD and EF values of Au@13-MC-1(d _Au=8.3 nm)were 2.3×10^-12 mol/L and 1.26×10⁷,respectively.Moreover,the SERS substrates of Au-loaded micelles have excellent reproducibility.In this work,Au-loaded cellulosic micelles were prepared through the thiol-ene click reactions,self-assembly and photo-reaction,and were used as SERS substrates for trace detection of MB.Which provides scientific data for design and preparation of cellulosic functional materials and has academic value and application prospect.