Mentioning nanomaterials, perhaps everyone is no stranger. The research field of nanomaterials has made the development of nanotechnology extremely rapid, and the research on gold nanoparticles has gradually increased. Therefore, fully understanding the synthesis and properties of gold nanoparticles will help people to better develop and utilize gold nanomaterials. So why is it playing such an important role in today's biological and medical fields? What is the nature of gold nanoparticles? Let me introduce you one by one! 

Physical properties of gold nanoparticles

1. Optical effect

Depending on the particle size, gold nanoparticles can selectively absorb and scatter some wavelengths of light, where absorption is dominant, and scattering is only a small fraction. The absorbed light is mainly located in the green light region, and the wavelength range is around 520 nm. According to the principle of complementary color, the gold nanoparticle solution is red due to the absorption of green light.

 

1. Small size effect

The most important small size effect of gold nanoparticles is surface plasmon resonance. The surface of the particle is affected by the electromagnetic wave of the incident light to generate electron cloud resonance, and surface plasmon resonance occurs in the visible region of 520 nm. For gold nanoparticles with different particle sizes, the maximum value of surface plasmon is different. As the particle size increases, the maximum value of surface plasmon shifts to a longer wavelength.

 

1. Surface effect

Since the size of the nanoparticles constituting the gold nanoparticles is small, the number of atoms occupied by the surface of the particles is far more than the number of atoms occupied by the surface of the non-nano material particles of the same mass, and the ratio of the number of surface atoms to the total number of atoms of the gold nanoparticle particles A sharp increase with the decrease in particle size causes a large change in the surface area, surface energy and surface binding energy of the particles, and the various specific effects produced thereby are collectively referred to as the surface effects of gold nanoparticles.

 

1. Macroscopic quantum tunneling

Tunneling refers to the ability of gold nanoparticles to penetrate the barrier. It has been found that the magnetization of gold nanoparticles and the magnetic flux and charge in quantum coherent devices also have tunneling effects. The tunneling effect of the macroscopic physical quantity of such gold nanoparticles is called the macroscopic quantum tunneling effect.

 

1. Dielectric confinement effect

The gold nanoparticle particles are dispersed in a heterogeneous medium. When the refractive index of the medium differs greatly from the refractive index of the nano gold particles, a refractive index boundary is generated, resulting in field strength and internal field strength of the gold nanoparticle particles relative to the incident. The field strength is significantly enhanced. This localized field strength enhancement is known as the dielectric confinement effect of gold nanoparticles.

 

1. Long-term effect

When the size of the gold nanoparticles is reduced to a very low value, the phenomenon that the electron energy level near the Fermi level changes from quasi-continuous to discrete energy levels occurs.

Chemical properties of gold nanoparticles

1. Fluorescent properties

After the gold nanoparticles are encapsulated by some probing groups, they undergo fluorescence energy transfer due to resonance energy migration. The size and shape of the gold nanoparticles and the distance between the molecules have a major impact on the rate of radiation and non-radiative transition. The fluorescence properties of gold nanoparticles have been studied under various conditions, including femtosecond radiation and steady-state investigation of the interaction between thiol and gold nucleus. Fluorescent gold nanoparticles have a good application prospect in biophotonics and materials science.

 

1. Electrochemical properties

The surface of the gold nanoparticles has an electric double layer capacitor, which acts as a nanometer-scale electrode. It is found that the 15 oxidation states of gold nanoparticles can perform such redox charge and discharge behavior. This electrochemical property of gold nanoparticles is related to the number of gold atoms contained in the central core of the particle and the alkyl protecting stabilizing group on the surface.

 

1. Adsorption characteristics

Gold nanoparticles are composed of a finite number of gold atoms, and the crystal field environment and binding energy of the atoms on the surface of the particles are different from those of the internal atoms. Therefore, there are many floating sites on the surface, which have unsaturated properties and are easily combined with other atoms. As a result, the gold nanoparticles have high activity and are easy to adsorb and chemically react with other groups. According to the special adsorption characteristics of gold nanoparticles, it can be supported on other supports to prepare highly active gold nanoparticle catalysts. 

 

1. Supramolecular and molecular recognition properties

The supramolecular and molecular recognition properties of gold nanoparticles refer to the controlled assembly behavior of gold nanoparticles. The chemical nanoparticles are used to control the surface of gold nanoparticles under the action of hydrogen bonds, van der Waals forces, chemical covalent bonds, etc. The formation of a supramolecular structure can be induced by special molecular recognition functional groups, other nanoparticles, or assembly of a specific substrate.

 

• The advantages of gold nanoparticles

Compared to gold nanorods, gold nanoparticles have incomparable advantages:

1. The nature is stable.
2. The preparation is simple.
3. The particle size is uniform.
4. Strong affinity.
5. Good biocompatibility.
6. Easy to modify the biomolecule.
7. Gold nanoparticles of different shapes and sizes can be obtained by controlling different synthesis conditions and synthesis methods.

Through my introduction, is there a great interest in magical gold nanoparticles? Click on the other searches to learn about the application of gold nanoparticles!

 

References

[1] YUAN Shuai, LIUZheng, MASu. Application Status and Research Progress in the Physical and Chemical Properties, Preparation Methods and Modification Techniques of Gold Nanoparticle. 

[2] Du bertret B, Calame M, Libchaber A J. Single-mismatch detection using gold-quenched fluorescentolionucleotides[J]．Nature Biotechn, 2001, 19 (2) :365.