DNA-Functionalized Quantum Dots

DNA-functionalization of quantum dots is the attachment of strands of DNA to the surface of a quantum dot. Although quantum dots with Cd have some cytotoxic release, researchers have functionalized quantum dots for biocompatibility and bound them to DNA in order to combine the advantages of both materials. Quantum dots are commonly used for imaging biological systems in vitro and in vivo in animal studies due to their excellent optical properties when excited by light, while DNA has numerous bioengineering applications, including: genetic engineering, self-assembling nanostructures, protein binding, and biomarkers. The ability to visualize the chemical and biological processes of DNA allows feedback to optimize and learn about these small scale behaviors.

Quantum dots are inorganic nanocrystal semiconductors that behave exceptionally well as fluorophores. In the field of biology, fluorophores are one of the few tools that allow us to peer inside of a live biological system at a cellular level. As a fluorophore, the size of a quantum dot directly reflects the wavelength of light emitted, allowing for a highly tunable color spectrum. Since the size of quantum dots are controllable and an increased size produces an increased wavelength range of emission, researchers are able to paint pictures on the cellular and sub-cellular levels with this technology. The current problem with common CdSe-ZnS quantum dots is that Cd is toxic to cells

To prevent this problem researches are developing ways to modify the quantum dot surfaces for biocompatibility, in addition to the development of Cd-free quantum dots (“CFQDs”). After a surface modification has been made to limit toxicity, the particle can be further coated with a hydrogel or bioconjugate layer to selectively bind to DNA, which may then be used for cellular or molecular level detection.

In order to coat the toxic Cadmium ions of the CdSe core, hydrogel layers may be used to coat quantum dots for biocompatibility. The purpose of the outer ZnS shell in this case is to interact with dangling bonds, in addition to maintaining the fluorescent strength of a functional quantum dot fluorophore. Within a hydrogel encapsulation, the ZnSe shell surface may be charged to bind to the hydrophobic interior of a micelle, which then allows the hydrophilic exterior to remain in contact with an aqueous solution (i.e. the human body and most other biological systems). The hydrogel layer works as a simplified intermediary bond for DNA or other organic materials.

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