Quantum Dots as Semiconductor Nanocrystals in Biomedical ApplicationsQuantum Dots as Semiconductor Nanocrystals in Biomedical Applications

Author: Hajira Mahmood

QDs are ultra-small nanocrystals (1–15 nm) based on semiconductors which possess remarkable intrinsic capabilities. The physicist Alexei Ekimov, who focused his study on semiconductors, initially reported on them in the 1980s. QDs are categorized into 12 categories depending on their chemical composition and where the elements that make them up are located in the periodic table. Tetravalent elements, like carbon, silicon, and germanium, have four electrons in their outermost shell. These elements have common physico-chemical characteristics, such as being metalloid and having semiconducting electrical properties, with group IV A QDs. The bulk of QDs have a heavy metal core with a bandgap silicon shell surrounding it. Examples of such core materials are CdTe, PbSe, ZnSe, or CdS with a SiO2 shell surrounding them. This raises the theoretical quantum yield and fixes the surface defect. QDs based on semi-conducting polymers (P dots) or QDs depending on simply one semiconductor element, including Si QDs, are exceptions to this typical composition. Based on a new semiconducting polymer dubbed NIR800, which emits lights in the near infrared range (~800 nm), Chen et al. created P dots that enable intriguing medical applications, including as in in-vivo imaging and flow cytometry, among others.

Small tiny particles, tunable composition and properties, higher yield of quantum dots, high luminescence, and periodic emission of light (blinking) are some of the intriguing features of QDs that have drawn interest from a wide range of applications, including solar cells, light-emitting diode (LED) technology, and biomedical uses like drug delivery, imaging, and cancer photodynamic therapy. One of the main things that makes QDs appealing is their optical qualities, which can be adjusted.

A higher band gap energy is required for smaller QDs, which raises the energy of the emission photon or subsequently shortens the emission wavelength of light, and vice versa. Because of this, QDs’ transparency depends considerably more on size than on material, which can be used to adjust the particle size in order to modify the electromagnetic spectrum generated by the substance ranging from the ultraviolet to the far infrared.

Quantum dots have gained significant attention in biomedical applications due to their unique optical properties and potential in various domains such as bio imaging, bio sensing, and regenerative medicine. While semiconductor quantum dots offer high photoluminescence and quantum yield, they are limited by toxicity and susceptibility to oxidation. However, carbon quantum dots have emerged as a promising alternative to conventional semiconductor quantum dots, offering high quantum yields and biocompatibility. Additionally, graphene quantum dots have shown considerable promise in regenerative medicine and stem cell imaging due to their superior properties such as photo stability and biocompatibility. Furthermore, colloidal quantum dots have been properly functionalized with controlled interfaces, making them a new class of optical probes extensively used in biomedical research. These quantum dots have been demonstrated to have extensive use in bio imaging applications, with some showing high photoluminescence quantum yields as well as being highly photo stable. Moreover, quantum dots have been explored for their potential in bioelectronics medicine for neurological diseases, indicating their promise for future applications in this field. It is important to note that the use of traditional semiconductor quantum dots in cellular imaging, sensing, and biomedical applications is limited due to the involvement of toxic elements such as cadmium. However, carbon quantum dots have been identified as superior in properties such as good luminescence, photo stability, water solubility, and biocompatibility, making them suitable for biomedical applications.

Quantum dots have shown great promise in biomedical applications due to their unique optical properties, making them suitable for imaging, sensing, and diagnostics. They have been used in various optical imaging experiments in vitro and in vivo, demonstrating their potential in sensitive optical molecular imaging and monitoring. Additionally, quantum dots have been explored for use in cancer cell imaging and diagnostic applications, indicating their potential in the field of oncology. Furthermore, the development of non-toxic quantum dots, such as indium phosphide-based quantum dots, has expanded the possibilities for biomedical applications, addressing concerns about the toxicity of traditional heavy metal-based quantum dots.

However, despite their potential, the use of quantum dots in biomedical applications is limited by concerns about their toxicity. The inherent toxicity of core materials, such as cadmium and lead, in conventional quantum dots has raised significant concerns, particularly in the context of cancer-related imaging and diagnostics. Moreover, the short shelf-life of water-soluble quantum dots due to colloidal instability represents a major drawback to their exploitation in biomedical applications. These limitations underscore the need for further research and development to address the toxicity and stability issues associated with quantum dots to fully realize their potential in biomedical applications.

Quantum dots, particularly carbon and graphene quantum dots, have shown great promise in biomedical applications due to their unique optical properties, biocompatibility, and potential for use in bio imaging, bio sensing, and regenerative medicine. These properties make them attractive candidates for various biomedical research and applications. In conclusion, while quantum dots offer unique optical properties that make them attractive for biomedical applications, their limitations, particularly related to toxicity and stability, need to be addressed to harness their full potential in sensitive imaging, diagnostics, and molecular detection assays.

Also read: Comparison of Conventional Verses Green Synthesis of Nanoparticles


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