Nanoparticles for Therapeutic Vehicles-Quantum Dots


Quantum dots (QDs) refer to nanocrystals with a particle radius smaller than the Bohr radius of their exciton. The three-dimensional dimensions are all less than 100 nm, and their particle size is between 2 and 10 nm. QDs mainly include carbon quantum dots and graphene quantum dots. Their photoluminescence and light stability are conducive to monitoring in vivo drug delivery and tumor diagnosis. They are commonly used in targeted drug delivery, bioimaging, immunoassay and detection, and biomolecules mark and other fields. The current applications of QDs in drug delivery are concentrated in two areas: as a drug carrier and used to mark and track drug delivery.

Carbon Quantum Dots (CQDs)

CQDs are carbon nanomaterials with a size of less than 10 nm. It was accidentally discovered by the Scrivens research group when purifying single-walled carbon nanotubes. This discovery filled the gap in the research of zero-dimensional carbon nanomaterials in the carbon nanomaterial family. Compared with other quantum dots, CQDs have high chemical stability, low toxicity, ability to absorb broadband light, and excellent photoluminescence properties. The surface of CQDs is rich in carboxyl groups, so it has good water solubility and biocompatibility, and can be synthesized on a large scale at low cost. In addition, CQDs are suitable for surface passivation and can be chemically modified by a variety of polymers, inorganic, organic, and biological materials. Gong et al. developed hollow CQDs doped with phosphorus and nitrogen. The characteristics of small particle size, hollow structure and rich nitrogen groups give CQDs fluorescence characteristics, which can be used for in vivo and in vitro drug monitoring. At the same time, as a carrier of doxorubicin (DOX), it can enhance the intranuclear delivery of DOX and tumor accumulation, effectively inhibiting tumor growth. The modified CQDs not only can be used for therapeutic detection, but also can trigger the targeted release of drugs by the tumor extracellular microenvironment.

Graphene Quantum Dots (GQDs)

GQDs are quantum dots that convert graphene with a two-dimensional structure into a quasi-zero-dimensional structure while maintaining the inherent layered structure of graphene.

It has small lateral size and abundant peripheral carboxyl groups, which is more compatible with biological systems. GQDs have similar performance to CQDs, while avoiding the limitations of CQDs in terms of size effect and quasi-spherical structure. GQDs can have good drug delivery capabilities without any modification. However, GQDs still have the problems of poor water solubility and low quantum yield. It is necessary to improve the performance of all aspects of GQDs through reasonable modification. GQDs play a role in photodynamics and drug delivery in drug delivery systems, and GQDs are used in near-infrared laser irradiation. Under the influence of light and heat, it effectively destroys tumor cells. Under the action of the magnetic nanospheres, it has the synergistic effect of magnetic field-mediated mechanical stimulation, photothermal damage, photodynamic toxicity and chemotherapy, and can destroy tumor cells in multiple ways at the same time. GQDs, as nanocarriers, have a retention effect in solid tumors, which prolongs the cytotoxic effect of the loaded drugs and better kills tumor cells.

Application of Quantum Dots in Medical Field

Tumors are one of the main causes of human death, and the prevention and treatment of tumors is currently an important public health issue. The reason why the traditional drug-carrying system has a low cure rate for tumors is that, on the one hand, the traditional drug-carrying system is not highly targeted and does not achieve a certain specific distribution in the body, causing the body's own normal cells to be severely damaged, especially It has serious adverse reactions to the hematopoietic system and immune system and affects the effect of tumor treatment; on the other hand, it is difficult to overcome the weak acidity of tumor tissues, high protein and enzyme expression, abnormal temperature gradients, endosomes and lysozymes in traditional drug delivery systems. The body has a unique microenvironment such as different acidic conditions, and the residence time is short, and the drug cannot be effectively delivered to the interior of the tumor cell, resulting in the low efficiency of the drug. How to safely and efficiently deliver drugs to tumor cells and play a role is a problem that needs to be solved urgently in tumor treatment. Therefore, the treatment of tumors requires a new drug-carrying system. In recent years, researchers have gradually shifted their research focus to the field of carbon nanomaterials, such as carbon quantum dots.

Studies have shown that CQDs have small particle size, good dispersibility and water solubility, low cytotoxicity, good biocompatibility, strong cell uptake and cell permeability, adjustable emission wavelength, strong fluorescence emission, high light stability, resistance Many advantages such as photobleaching, rich surface functional groups and easy functionalization. Based on these advantages, CQDs are widely used in the fields of biosensing, drug-loaded therapy and bioimaging. Among them, the application in the field of drug-loading, especially the anti-tumor drug delivery system based on CQDs has attracted extensive attention and research.

Quantum dot drug delivery system

Figure 1. Quantum dot drug delivery system.

According to the difference between the tumor microenvironment and the normal physiological microenvironment, such as: low pH, strong reducibility, differential enzyme expression, high reactive oxygen species and sensitivity to sound, light and heat, different types of CQDs and anti-tumor drugs are passed The combination of non-covalent or covalent methods forms a CQDs drug delivery system with various response methods. Compared with traditional drug chemotherapy, they can enter the tumor site through the high permeability and retention (EPR) effect of the tumor. In their special environment, the non-covalent or covalent relationship between CQDs and anti-tumor drugs The connection is broken, thereby effectively delivering the drug to the tumor tissue, improving the utilization and curative effect of the drug, and reducing the toxic and side effects of the drug on the human body. Secondly, compared to traditional nano-drug delivery systems, they can not only retain the original anti-tumor effect, but also can track drug delivery and cell status by means of fluorescence imaging. Therefore, it has great potential for the tracking and research of drugs in the body and prognostic evaluation.

References:
1. Zhao XB, et al.; PEGylated multi-walled carbon nanotubes as versatile vector for tumor-specific intracellular trig gered release with enhanced anti-cancer efficiency: optimization of length and PEGylation degree. Colloids Surf B. 2018, 168: 43-49.
2. Wang YF, Hu AG.Carbon quantum dots: synthesis,properties and applications. J Mater Chem C. 2014, 2 (34): 6921-6939.
3. Jiao J, et al.; Fluorescent carbon dot modified meso porous silica nanocarriers for redox-responsive controlled drug delivery and bioimaging. J Colloid Interface Sci. 2016, 483: 343-352.
4. Lim SY, et al.; Carbon quantum dots and their applica tions.Chem Soc Rev. 2015, 44(1): 362 -381.
5. Gong XJ, et al.; Phosphorus and nitrogen dual doped hollow carbon dot as a nanocarrier for doxorubicin delivery and biological imaging. ACS Appl Mater Inter. 2016, 8(18): 11288-11297.
6. Yan X, et al.; Colloidal graphene quantum dots with well defined structures. Acc Chem Res. 2013, 46 (10) : 2254-2262.
7. Wang C, et al.; Enhancing cell nucleus accumu lation and DNA cleavage activity of anti-cancer drug via graphene quantum dots. Sci Rep. 2013, 3( 6154) : 2852.
8. Zheng M, et al.; Integrating oxaliplatin with highly luminescent carbon dots an unprecedented theranostic agent for personalized medicine. Advanced Materials. 2014, 26(21): 3554-3560.

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