Preparations,Properties,and Structural Controls Of Gold Nanorod (AuNR) And Mesoporous Silica-coated AuNR

The unique, tunable, and anisotropic property of lacalized plasmon resonance(SPR) provide gold nanorod(AuNR) great research and application prospects in fields of analytics, detection, biology, theranostics, catalysis, optics, photonics, and so on. Therefore, it is of great value to conduct the fundamental study of AuNRs concerning stratagies of synthesis, property, surface modification, and structural control. In this paper, some aspects of these related topics were specifically chosed and inverstigated based on plenty of literature surveys. A series of research findings have been gained, which included the influence of experimental parameters on AuNRs yield and monodispersity, investigations of encapsulating AuNR with mesoporous silica and the survey of the coating layer, SPR-based enhancement of fluorescence from Au nanocluster, and structural control of silica-coated AuNR(AuNR@mSiO2). The detail contributions are as follows:1. Synthesizing AuNRs with high yield and excellent monodispersity contributes to an important part concerning studies of the AuNRs synthesis method. Previous works had revealed that the existence of a trace amount of iodine ion(I-) in the growth solution, which was brought in by the reactant of cetyltrimethylammonium bromide(CTAB), would severely deterioratethe the purity of AuNRs product. By comparing the experimental parameters and results of four synthesis methods, as well as combining the latest mechanism surveys on AuNR growth, we concluded that the acquisition of high yield and excellently monodisperese AuNRs was attributed to several factors: the decrease in dosage of CTAB could reduce the concentration of I- at the same time, thus weakening the contamination effect; a rise in the Ag+ concentration can also provide an increased resistance to the I-; at a lower pH and reductant concentration, anisotropic growth of the particle was favored.2. The mesoporous silica coating of AuNR can provide the structure with advantages of improved stability, easy of modification, better biocompatibility, and excepetional mesoporous texture. We examined the coating method in application to AuNRs that were synthesiszed by different methods, as well as studied the thickness control, surface modification, and the pore structure of the silica coating layer. Results showed that the resedual additive and its property has important influences on the successful encapsulation of AuNR and the pore size of the coating layer. Besides, increasing the thickness of the coating layer with a solid or a porous silica structure can be acquired by an improved st?ber method or a tiny modification of mesoporous coating process. In addition, the ammonium- functionalization of the silica surface was found to be easily obtained, and the use of Tetrakishydroxymethyl phosphonium chloride(THPC) protected AuNPs for the adsorbing test also showed the modified silica structure retained its porous feature.3. Au25(SR)18 nanocluster was reported to be a good candidate in sensing, imaging, and other applications due to the unique fluorescence property and good stability. The use of glutathione(GSH) as ligand further provides the structure with excellent biocompatibility. However, the fluorescent quantum yield of Au25(SG)18 is too low to be widely applied. We explored the fluorescenct enhancement technique by using the SPR of AuNR@mSiO2 and AuNS@mSiO2, respectively. Results revealed the fluorescent quenching occurred in both cases, suggesting that the changes of the environment and the ligand state may be responsible for the outcomes.4. Structural control of AuN R@mSiO2 was conducted by etching the AuN R and dissolving the silica shell. O2 can penetrate through the mesoporous silica shell and selectively etch the AuNR, providing the shortening control of AuNR that showed potential in controllably tuning the SPR of AuNR@mSiO2. The solvent that used for the experiment and the thermal treatment that was performed before the etching can significantly affect the structural evolution of AuNR@mSiO2. In ethanol solution, the silica shell was rigid, a longer time of thermal treatment can accelerate the etching reaction; as the etching proceeded, a cavity-possessing, rattle-type, and howllow AuNR@mSiO2 structures can be produced. When ethanol-water was used as the solvent, the thermal treatment can cause the homogeneous reduction of silica shell thickness; the etching process in this condition can generate shape-adaptive silica-coated structure.5. Application of the anisotropic SPR property of AuNR intrinsically calls for anisotropic functionalization. We proposed that, by simply managing the coating parameters and conditions, the structural disparity of CTAB bilayers, which caps on the AuNR and possesses defects at the AuNR ends, can be employed to induce the end- and side-selective silica coating of AuNR. Evolutions of the site-selective coating behavior can be directly managed by controlling the dosage of tetraethylorthosilicate, which was the precursor of silica. The mechanism verification tests using non-rod- like AuNPs showed that the selective coating process was curvature-dependent.