Study On Synthetic Mechanism Of Gold Nanorods And Their On-demand Preparation

Gold nanorods(Au NRs)have a wide range of applications in the field of biology,medicine,catalysis,sensing,and optical storage due to their physicochemical properties including size/shape-dependent surface plasmonic resonance properties,good biocompatibility,diverse surface functionalization,which render them receive great attention from researchers for a long time.To further extend their applications in surface-enhanced Raman scattering(SERS),photothermal imaging and therapy.,it is desirable to control the dimension of Au NRs.After nearly three decades of effort,despite the remarkable advancements have been made to control the dimension of Au NRs,there are still some problems.For instance,the length and width of Au NRs are generally changed simultaneously by the one-step seeded growth method,thus it is difficult to achieve the synthesis of Au NRs with a fixed width(less than 30 nm)but different length by simply adjusting one certain reaction condition.At present,Au NRs are firstly synthesized in multiple batches by adjusting various reaction conditions,and then the required Au NRs are selected from different batches.Therefore,it remains a challenge to synthesis of Au NRs with a fixed width but different lengths by simply adjusting one certain reaction condition.In addition,the widths of Au NRs prepared by traditional seeded growth methods is generally smaller than 30 nm,while Au NRs with width greater than 30 nm are mainly prepared by introducing additional additives(such as aromatic or sodium oleate),and it still needs to simultaneously adjust multiple experimental parameters,moreover,it is difficult to achieve the adjustment and ensure the reproducibility of their dimension.Based on the above problems,this paper takes the on-demand preparation of Au-NRs as the research goal.The synthetic mechanisms of Au NRs which is prepared by one-step seeded growth method were firstly studied to understand the role of multiple parameters in their growth,and thus achieving the rational synthesis of Au NRs.Then,additional additives(heptanol and dodecanol)were introduced into the solution of Cetyltrimethylammonium Bromide(CTAB)molecules to change their micellization behavior in water,thus,Au NRs with a large width scope and a fixed width(less than 30 nm)but different lengths were successfully synthesized by adjusting one single experimental parameter.This paper is divided into five chapters,and the main contents of each chapters are as follows(Chapter 1 is the introduction):In Chapter 2,firstly,a series of Au NRs with different dimensions(lengths and widths)were synthesized by tuning the[Ag+]or[H+]at a fixed HAuCl4 and concentration of Au-NP seeds.Then,the lengths and widths of the as-prepared Au NRs were simulated with the[Ag+]and[H+]as the two main variables,respectively.It is found that beside the known effect of underpotential deposition of silver ions(AgUPD)and effect of pH-dependent reaction rate,respectively,Ag,ions and H+ ions also can adjust the lengths and widths of Au NRs by affecting the size of the mixed CTAB micelles.Lastly,based on the new understanding of the synthetic mechanism of Au NRs,the rational synthesis of Au NRs in the present dimension scope(length ranging from 23 to 132 nm and width ranging from 5.4 to 27 nm)can be achieved by judiciously controlling the[H+],[Ag+]and concentration of Au-NP seeds,that is,Au NRs with a fixed length but different widths,Au NRs with a fixed width but different lengths and Au NRs with a fixed AR but different lengths and widths,which provide reliable photothermal conversion materials for photothermal therapy of cancer.In Chapter 3,firstly,heptanol was introduced as secondary templating agents when synthesis of Au NRs by one-step seeded growth method,a relatively low concentration of silver ions is needed(0.06 mM,the lowest concentration of silver ion that can obtain a uniform Au NRs)in order to synthesize Au NRs with a large width scope.At this moment,the additional heptanol molecules can not only alter micellization behavior of CTAB in water,but also help silver ions impact the symmetry-breaking efficiency of additional Au-NP seeds in addition to enhance the utilization of gold precursors.Then,the synthesis of Au NRs with a large width scope(6.5?175 nm)were successfully achived by changing the concentration of HAuCl4 or Au-NP seeds at the fixed concentration of silver ions of 0.06 mM.Next,the synthesis of Au NRs in the presence of other fatty alcohols with properly long alkyl chains(number of carbon atoms in alkyl chain:7?12)were studied,which demonstrated the generality and versatility of the present strategy for synthesis Au NRs with flexible controlled dimensions.Lastly,a series of arrays of vertically aligned Au NRs were further fabricated as SERS substrates by using these as-prepared Au NRs of different dimensions,and further study their detection sensitivity in SERS detection and their application in rapid detection.The results showed that when arrays of vertically aligned Au NRs(120 nm × 90 nm)are used as SERS substrates,they can realize the ultra-high sensitivity detection of the SERS signal of the probe molecule(eg.the ultralow limit of detection for crystal violet of 10-16 M).Thanks to their ultralow limit of detection,they also can be used for rapid detection and identification of residual harmful substances with an ultralow concentration,such as residual malachite green in aquatic products(10-15 M).In Chapter 4,firstly,dodecanol was introduced as secondary templating agents when synthesis of Au NRs by one-step seeded growth method,a relatively high concentration of silver ions is needed(>0.24 mM)in order to synthesize Au NRs with a fixed width(less than 30 nm)but different lengths.At this moment,the additional dodecanol would fine-tune the structure of the mixed CTAB micelles and make it tighter,thereby finely tuning the amount of silver ions adsorbed on the facets of the Au-NP seed,and thus cooperating with silver ions to impact the symmetry breaking efficiency of additional Au-NP seeds,and finally achieving the adjustment of the length of Au NRs at fixed width.Then,a series high quality Au NRs with a fixed width(6.5,14,and 23 nm)but different lengths(23?35,69?109 and 75?130 nm)were successfully synthesized by adjusting the concentration of dedocanol sololy at the fixed of other reaction conditions and at a high concentration of silver ions(0.24-0.30 mM).In addition,the length scope(16?46,26?109 and 38?130 nm)of the Au NRs at a fixed width(6.5,14,and 23 nm)can be further extended by adjusting the concentration of HAuCl4,HQ,and silver ions.In Chapter 5,we have summarized and forecasted the above works.In summary,in this paper,the synthetic mechanism of Au NRs which is prepared by one-step seeded growth method was studied,and the main role of hydrogen ions and silver ions in the growth of Au NRs was revealed,thus the rational synthesis of Au NRs in the present dimension scope(length ranging from 23 to 132 nm and width ranging from 5.4 to 27 nm)can be achieved.In addition,additional additives(heptanol and dodecanol)was introduced as secondary templating agents,and the synthesis of Au NRs with a large width scope and a fixed width but different lengths were successfully achieved by adjusting one certain reaction condition.