Synthesis And Surface Selective Modification Of Gold Nanorod

Gold nanorod has anisotropic local surface plasmon resonance（SPR）property,which has significant research and application value in the fields of analysis,detection,sensing,catalysis and biomedicine.It is important to study the fabrication and surface selective modification of nanorod based on their size,structure and optical properties.Recent studies have shown that the synthesis of gold nanorod with new reducing agents has advantages in regulating the morphology,structure,absorption spectrum and other properties of the rods,and has promoted the understanding of the anisotropy growth process and mechanism of nanoparticles.Using the special properties of the surface structure and adsorbed molecular layer of gold nanorod,the selective modification of different parts of the nanorod surface can be obtained,showing the important value of precise selectivity and efficient utilization of anisotropic SPR.Accordingly,the following work is carried out in this paper:1.The traditional reducing agent,ascorbic acid,has strong reducibility,resulting in a low yield of synthesized gold nanorod and a narrow LSPR wavelength range.Appropriately weakening the reducing atmosphere is beneficial to improve the yield,size tunability and monodispersity of gold nanorod.Therefore,it is of great value to explore the synthesis methods and characteristics of gold nanorod under different reducing atmospheres.In this part,the preparation of gold nanorod with weakly reducing m-phenylenediamine was studied.The results show that the synthesized gold nanorod has good monodispersity,high yield,a maximum LSPR wavelength of 1054 nm,the aspect ratio is 2.2～5.4,and a small diameter,which is suitable for the synthesis of gold nanorod with small diameter and large LSPR wavelength.In addition,the effects of the amount of silver nitrate,seed crystal,reducing agent and CTAB on the preparation of gold nanorod were investigated,and it was found that:changing the amount of silver ions,the position of the LSPR absorption peak of the rods can be adjusted in the range of 680 nm to 1050nm;increasing the amount of seed crystals can make the morphology of gold nanorods change from dumbbell-shaped to regular rod-shaped,while excessive seed crystals will lead to the increase of by-products;the amount of reducing agent did not significantly affect the position of the LSPR absorption peak of the product;increasing the concentration of CTAB within a certain range,the LSPR absorption peak was red-shifted,which promoted the growth of gold nanorod along the long axis.2.The relatively weak reducing atmosphere is significantly beneficial to the anisotropic growth of nanorod.It is of great significance to deeply study the effect of different reducing atmospheres and expand the understanding of its laws for further revealing the anisotropic growth mechanism of nanoparticles.So far,there are few reports on the preparation of gold nanorod under extremely weak reducing atmosphere.In this chapter,the preparation of gold nanorod was studied using catechol as reducing agent,which has extremely weak reducing property.The results show that gold nanorod can be successfully prepared at higher temperature and higher concentration of catechol.The LSPR wavelengths of the products range from 580 nm to 920 nm,and the corresponding nanorod has an aspect ratio of 1.6 to 4.9,with high yields,good monodispersity,and small diameters.In addition,the influence of various experimental conditions was studied,and the results showed that changing the amount of silver ions could control the position of the LSPR absorption peak;increasing the amount of reducing agent would inhibit the growth of gold nanorod,resulting in a smaller size;increasing the amount of seed crystals could significantly decreasing the diameter of the rod;increasing the CTAB concentration promotes the growth of gold nanorod along the long axis.3.In-depth study and efficient utilization of the anisotropic SPR properties of gold nanorod are highly dependent on anisotropic modification of nanorod,that is,selective modification of different parts of the surface.At present,the selective modification of the side parts of gold nanorod mostly uses thiol molecules to passivate the two ends of its,and then indirectly"activate"its sides,so as to obtain selective side modification.This technology has higher requirements on experimental conditions and operations,and the process is cumbersome,and the reproducibility of the results needs to be improved.Based on the research and understanding of the process and mechanism of gold nanorod coated by mesoporous Si O₂,this chapter studied the method of selectively modifying the sides of gold nanorod by mesoporous Si O₂ without the assistance of thiol molecules,and analyzed the influence of various experimental parameters.The results show that side-selective modification structures can be obtained when CTAB is 20～25 mmol/L,temperature is 40℃,and p H is 10.5.Increasing the CTAB concentration,raise the temperature,and lower or higher p H all lead to defect in the coating layer,and the products obtained by decreasing the concentration of CTAB and temperature are complete coating structures.In addition,increasing the concentration of ethyl orthosilicate within a certain range can increase the thickness of the Si O₂ coating layer;nanorod with smaller diameter is easier to obtain lateral coating.The mechanism verification of the coating behavior was carried out with nanoparticles with other morphologies,and the results preliminarily showed that the selective coating behavior was guided by the surface curvature,and the low-curvature surface had a significant coating advantage over the high-curvature surface.4.Based on the consideration of the applicability of the extended surface-selective modification structure,the further modification properties of the prepared structure and the mesoporous structure of the coating layer were investigated.The surface amination of the selectively modified structure was carried out with（3-aminopropyl）trimethoxysilane reagent for the loading of small gold nanoparticles and Cd Te fluorescent quantum dots.The results show that the aminated structure has good stability;the Si O₂ coating layer maintains a good mesoporous structure,and can successfully adsorb gold nanoparticles and Cd Te quantum dots;the fluorescence of Cd Te quantum dots was quenched after adsorption.