Introduction

In recent years, nanomaterials and nanotechnology have increasingly entered the clinical application stage. Gold nanoparticles have very unique physical and chemical properties. And gold nanoparticles are relatively safe, easy to prepare, and very stable. In addition to the small size effects, surface effects, quantum size effects, macro quantum tunnel effects, and dielectric effects of nanoparticles, gold nanoparticles also have unique electrical, optical, magnetic, catalytic effects. Therefore, gold nanoparticles have been widely used in the filed of biomedicine. In the treatment of tumors, gold nanoparticles have better penetrating power than traditional drugs, and their risks in diagnosis and treatment are lower than traditional drugs.

Structure and Properties of gold nanoparticles

Gold nanoparticles exhibit unique physical and chemical properties due to their different shapes and sizes. The gold nuclei of gold nanoparticles are essentially inert and non-toxic. The synthesis of gold nanoparticles is relatively easy, and the diameter range is controllable, generally in the range of 1 to 150 nm. Gold nanoparticles with different properties and sizes can control the release of drugs in different parts, so it is a good drug carrier. Various shapes of gold nanoparticles have been developed to meet different therapeutic needs.Gold nanospheres (AuNPs) are gold nanoparticles produced by reduction of chloroauric acid, with diameters ranging from 1 to more than 100 nm, and they are mainly used for imaging and radiosensitization. Gold nanoshells (AuNSs) are spherical with diameters ranging from 50 to 150 nm. The structure of the gold nanoshell includes a core of silicon dioxide and a thin gold shell. The optical properties of AuNSs can be adjusted by changing the diameter of the core and the thickness of the shell wall. Gold nanorods (AuNRs) are usually synthesized by the reaction of chloroauric acid on gold seeds using cetyltrimethylammonium bromide (CTAB) as a stabilizer. The size of AuNRs is usually 25-200 nm. The wavelength of the absorption peaks of AuNRs can be changed by changing the ratio of the length and diameter of these particles (ie, the aspect ratio). There are also other forms of gold nanoparticles, such as nanocages and hollow gold nanospheres.

Application of gold nanoparticles in tumor diagnosis

One of the differences between tumor cells and normal tissue cells is the difference in cellular metabolic activity. For example, in liver cancer cells, breast cancer cells, or melanoma cells, protein kinase (PKCa) is either overexpressed or has abnormal activity. Protein kinases can phosphorylate specific substrate peptides, resulting in changes in the net charge carried by the substrate peptides. When the substrate peptide and nanogold are mixed, the stability of the nanogold colloid is affected by the net charge before and after the substrate peptide is phosphorylated. The surface charge layer of the nanogold is destroyed by the large net charge of the substrate peptide, which will cause colloid aggregation Therefore, the activity or expression of protein kinase can be indirectly determined by whether or not nanogold is aggregated, so that tumor cells and normal tissue cells can be distinguished. Imaging with gold nanoparticles in the visible spectrum can only be applied to cancers on the skin surface. Optical imaging of most solid tumors in vivo needs to be performed in the near infrared spectral region of 780 to 2526 nm (especially 780 to 1100 nm). Changing the size, shape and composition of gold nanoparticles, or modifying the surface of gold nanoparticles can make the nanoparticles have high surface plasmon resonance absorption and scattering capabilities in the near-infrared spectral region. By connecting them with specific biological targeting molecules, gold nanoparticles can become a very effective imaging agent for tumor imaging. Studies have found that PEGylated gold nanoparticles, gold cages and gold rods all have good stability, biocompatibility, biodispersity, and osmotic retention effects, and can accumulate in large quantities at tumor sites. In the near-infrared spectral region, these types of gold nanoparticles have suitable local surface plasmon resonance peaks, so they can clearly develop tumor tissue.

Application of gold nanoparticles in tumor treatment

As a drug carrier, gold nanoparticles can improve the pharmacokinetics of drugs, thereby reducing non-specific side effects and achieving targeted drug delivery at higher doses. Gold nanoparticles can also be used in thermotherapy treatments. The mechanism of hyperthermia treatment involves the thermal stress response of cells at 42-47 °C, which causes the activation of cells and the activation of degradation mechanisms inside and outside the cell. The negative effects of hyperthermia on cells include misfolding and aggregation of proteins, changes in signal transduction, cell apoptosis, changes in pH, reduced perfusion and tumor oxygenation, etc. Gold nanoparticles such as gold nanorods (AuNRs) or gold nanoshells (AuNSs) have obvious advantages in the absorption and scattering of near-infrared light (wavelengths from 650 to 900 am). When exposed to electromagnetic radiation, especially near-infrared light, gold nanoparticles can generate heat through surface plasmon resonance effects. Because the peak of the absorption wave of gold nanoparticles is in the visible light range (450-600 nm), the absorption of near-infrared light by normal tissues is very small. Stimulating gold nanoparticles with near-infrared laser light can induce heat generation and hardly damage normal tissues. Therefore, gold nano-mediated photothermal therapy has the advantages of strong specificity and less trauma compared with traditional tumor treatment.

Conclusion

Gold nanoparticles have unique physical and chemical properties and have been a hot spot in tumor diagnosis and treatment. The application of gold nanoparticles in the detection of tumor markers and the imaging of tumors is the focus of researchers' attention. However, more studies are needed on the metabolism of gold nanoparticles in the body and its effect on normal cell activity, especially on gene expression or regulation.