Edit the synthesis of gold nanorods in this paragraph
Seed-induced growth has become the most effective method to synthesize colloidal solution of high-purity solvent-phase gold nanorods by chemical method. Cetyltrimethyl ammonium bromide (CTAB) is one of the most commonly used surfactants in the synthesis of gold nanorods.
Edit the characteristics of gold nanorods in this section.
Surface plasmon resonance
The surface plasmon resonance of gold nanorods will make them scatter and absorb light with specific wavelengths in visible and near infrared bands. Therefore, visible and infrared extinction spectra can be used to characterize the optical properties of colloidal solution of gold nanorods, that is, the surface plasmon resonance properties of gold nanorods. Dark field scattering method is also often used to characterize the light scattering characteristics caused by surface plasmon vibration of a single gold nanorod.
morphosis
Gold nanorods are rod-shaped gold nanoparticles, the length of which is continuously adjustable between 20 nm and 200 nm, and the width is between 5 nm and 100 nm. Scanning electron microscope and transmission electron microscope are often used to characterize the morphology and structure of gold nanorods. Among them, high-resolution transmission electron microscope can be used to characterize the lattice structure and surface crystal plane distribution of gold nanorods.
Surface crystal plane structure
Gold nanorods stabilized by cetyltrimethylammonium bromide can exhibit high exponential crystal faces in water. Its chemical activity is much higher than that of gold nanoparticles surrounded by other low-index crystal planes. The gold nanorods surrounded by high-index crystal planes can also be used as templates to induce the formation of high-index crystal planes of palladium, and the high-index crystal planes derived from them have extremely high catalytic activity and can be used for Suzuki coupling catalyzed by Qualcomm. [2]
Application of editing gold nanorods in this paragraph
Application in life science
1. In vitro diagnosis: The biosensor based on the surface plasmon resonance characteristics of gold nanorods can be used for in vitro diagnosis in biomedicine. See "Applications in Sensors" below for details. [3] 2. In vivo imaging: Gold nanorods have strong light scattering in the near infrared band, but the scattering background of organisms in this band is weak, which makes gold nanorods can be used as biological imaging contrast agents based on light scattering. Gold nanorods are superior to traditional dyes or dyes based on semiconductor quantum dots because of their high stability and low toxicity, and their light scattering effect has no failure path similar to fluorescence quenching. [4] 3. In vivo therapy: The total extinction of gold nanorods includes scattering and absorption. For gold nanorods with a diameter less than 10 nm, the absorption of light is much greater than the scattering, and the absorbed energy will eventually be converted into heat energy through lattice relaxation. [5] On the other hand, for organisms, the radiation in the near infrared band has a window effect, and the radiation in this band can penetrate the tissues of organisms with little loss. Therefore, gold nanorods can be used to manufacture photothermal therapeutic reagents with high light absorption cross section and excellent photothermal conversion efficiency in near infrared band. By coating a layer of polymer molecules with good compatibility with body fluids on the surface of gold nanorods, gold nanorods can be transported circularly in organisms for as long as 15 hours. Scientists have proved that gold nanorods and related nanostructures can kill cancer cells with a small light dose through photothermal therapy. [6]
Application in catalysis field
Under the same temperature and chemical and physical environment, gold nanorods coated with palladium or platinum have higher catalytic activity and better stability than pure palladium or platinum catalysts with the same dosage. Especially under the irradiation of light (such as sunlight), the gold nanorods in this composite catalyst can absorb light energy and convert it into heat energy. This photothermal conversion makes the local temperature on the surface of gold nanorods rise by tens to hundreds of degrees Celsius. On the one hand, this local temperature increase provides temperature activation for the catalytic reaction on the surface of nanoparticles, on the other hand, it saves the energy needed to heat the whole solution system. It is a greener and more energy-saving catalyst. Scientists believe that gold nanorods coated with palladium or platinum may have higher catalytic selectivity, but whether this proposition is established remains to be verified by experiments.
Application in sensor
1. surface enhanced Raman scattering: monodisperse or coupled gold nanorods have strong surface electric field enhancement effect, and can be used as Raman enhancer for surface enhanced Raman scattering. Compared with the traditional silver nanoparticle Raman enhancer, the gold nanorod Raman enhancer has higher physical and chemical stability, longer storage time and longer service life. This makes gold nanorods have excellent application opportunities in sensors based on Raman scattering signals. 2. Small molecule detection based on refractive index sensitivity: A few nanometers of ring around gold nanorods can significantly affect its surface plasmon resonance properties: with the increase of ring refractive index, the surface plasmon resonance peak of gold nanorods shifts red. The relative magnitude of redshift can be measured by refractive index sensitivity. Gold nanorods with this property can be used for the detection of trace molecules. [7] 3. Micro-molecule and ion detection based on nano-particle assembly: Under the action of some specific molecules or ions, bare or surface-modified gold nanorods will be assembled in order or reassembled in disorder. The assembly or reunion of gold nanorods will cause the change of their characteristic spectra (in some cases, the color change can be directly observed by the naked eye). Based on this principle, the existence of these specific molecules or ions in the solution can be detected, and then its content can be determined. 4. Detection of small molecules and ions based on energy level * * * vibration coupling effect: charged dye molecules can be adsorbed on the surface of gold nanorods through electrostatic interaction. When the * * * vibration energy level of plasma on the surface of gold nanorods degenerates with the absorption energy level of dye molecules adsorbed on the surface, the system will produce the * * * vibration coupling effect, which will cause the * * * vibration peak of gold nanorods to move greatly. Under the action of some other specific molecules or ions in the solution, the dye molecules electrostatically adsorbed on the surface will desorb and leave the surface of the gold nanorod, thus eliminating the * * * vibration coupling effect and making the * * * vibration peak of the plasma move backward. Based on this principle, the existence of these specific molecules or ions in solution can be detected.
Application in optical components
1. Near-infrared filter: Gold nanorods can be used to make filters because of their strong absorption in the near-infrared band. 2. Nonlinear optical elements: Due to the surface plasmon vibration, the surface electric field intensity of gold nanorods is greatly enhanced (up to 10e7 times), and this electric field enhancement effect reduces the threshold of irradiation intensity required to realize nonlinear effect, so it can be used to manufacture various nonlinear optical elements. 3. Polarizer: The gold nanorod has a plasma vibration mode parallel to the long axis direction and two degenerate plasma vibration modes perpendicular to the long axis direction, which are called axial surface plasmon vibration mode and radial surface plasmon vibration mode respectively. The vibration mode of radial surface plasmon is between 500-530nm, with small tuning range and weak intensity. The mode of long-axis surface plasmon can be continuously adjusted from visible light (550 nm) to near infrared (1550 nm) with the change of aspect ratio, and its intensity is much higher than that of radial mode, and it is a linear polarization mode parallel to the long-axis direction. If the gold nanorods are arranged in one direction, the light field component with polarization direction parallel to this direction will be absorbed by the axial plasma mode of the gold nanorods, while the light field component with polarization direction perpendicular to this direction will not be affected. Based on this principle, gold nanorod polarizers with wavelength ranging from 550 nm to 1550 nm can be fabricated.
Absorption-enhanced thin film solar cell
In order to save the amount of semiconductor raw materials, the absorption layer of thin-film solar cells can be as thin as several hundred nanometers. When the thickness of the semiconductor absorption layer is less than micron, it is not enough to absorb all the incident light. At this time, appropriate structures and materials are needed to increase the light absorption efficiency of the semiconductor absorption layer. Strong scattering gold nanorods can improve the light absorption efficiency of the absorption layer in thin film solar cells in this band because of their low photothermal energy loss and strong field enhancement effect in visible and near infrared bands, thus improving the overall photoelectric conversion efficiency of solar cells.
Nano-standard material
The colloidal solution of gold nanorods with extremely uniform morphology can be prepared by precisely controlled synthesis and post-treatment methods. The length of gold nanorods can be continuously adjusted from 20 nm to 200 nm, and the width can be continuously adjusted from 5 nm to 100 nm. This kind of gold nanorods with very small individual differences can be used as a standard reference for nano-scale.
Prevent forgery
Gold nanorods can have a continuous wavelength response from visible light (550 nm) to near infrared (1550 nm). Especially in the near infrared band, gold nanorods can become excellent anti-counterfeiting materials. Using gold nanorods that respond in different infrared bands, nano-infrared barcodes can be formed. This kind of barcode, which can not be distinguished by naked eyes, can display different combinations of numbers and even patterns on infrared display equipment to meet the high-end anti-counterfeiting requirements.
Optical information storage
The wavelength adjustability and polarization dependence of gold nanorods can be used to prepare large-capacity information storage devices. In May 2009, Professor Gu Min of Swinburne University of Technology and others published a paper in Nature, explaining how to make the next generation of large-capacity five-dimensional information storage media by using gold nanorods. Its manufacturing principle is that gold nanorods can respond to light with different wavelengths because of their different shapes, so researchers can record color information with different wavelengths on the same optical disc, and the original three-dimensional space greatly expands the storage capacity, which is a great progress compared with the existing DVD that can only record colors with a single wavelength. The fifth dimension of the optical disc is made by using the polarization characteristics of light, so that the optical disc can record multiple layers of information with different angles, and there will be no interference between the layers of information. Using the reported new storage technology, the existing DVD-sized optical disc can theoretically store 1600G data. In contrast, the capacity of existing DVD discs is generally around 4GB, while Blu-ray discs without DVD can only store 50G information. [8][9]
Nano optoelectronics
Nano-photonics based on surface plasmon polaritons has attracted extensive attention from the huge microelectronics industry in the world because of its infinite potential in manufacturing nano-photonic integrated circuits. The size of traditional photonics components is often limited to more than microns, but they can work at hundreds of terahertz (10 12 Hz) and run very fast. However, the size of microelectronic components has been reduced to tens of nanometers, but the highest working frequency is only Ghz (10 9 Hz), and the running speed is relatively slow. If photonic circuits can be integrated into microelectronic circuits, it will be possible to greatly improve the processing speed of traditional microelectronic chips. However, the size gap between photonic components and microelectronic components greatly hinders their integration, thus hindering the possibility of using photonic components to improve the running speed of microelectronic circuits. Because of this, nano-photonic integrated circuits based on surface plasmon become the key factor to solve this size matching problem. In order to realize the surface plasmon nanophotonic integrated circuit, we need those surface plasmon components corresponding to the basic microelectronic components. So far, the breakthrough work in this field has focused on passive surface plasmon components, such as plasma waveguides, resonators and couplers. However, the research on active surface plasmon components such as surface plasmon modulators and switches is very limited. Professor Wang Jianfang of the Chinese University of Hong Kong [1] reported a surface plasmon switch based on controllable * * * vibration coupling of gold nanorods. [10] This switch consists of a single gold nanorod and its surrounding photochromic molecules, and its size is less than 100 nm. Gold nanorods and molecules are encapsulated in silicon dioxide films. Its switching characteristics are triggered by ultraviolet light and monitored by dark field scattering technology. The trigger power and energy required to operate this single surface plasma switch are only about 13pW and 39pJ, and its modulation depth can reach 7.2dB. This optically controlled plasma switch can be used as a switching element in a nano-photonic circuit, so that it can be well coupled with microelectronic elements, and the problem of size matching between them can be solved.