Hydrogel encapsulation of quantum dots

In this form, quantum dots can be utilized in several applications that benefit from their unique properties, such as medical imaging and thermal destruction of malignant cancers.

They possess electrical properties between those of bulk semi-conductors and individual molecules, as well as optical characteristics that make them suitable for applications where fluorescence is desirable, such as medical imaging.

[2] The ZnS shell has a two-fold effect: Despite their potential for use as contrast agents for medical imaging techniques, their use in vivo is hindered by the cytotoxicity of cadmium.

To address this issue, methods have been developed to “wrap” or “encapsulate” potentially-toxic QDs in bio-inert polymers to facilitate use in living tissue.

[4] Another issue with CdSe(ZnS) nanoparticles is significant hydrophobicity, which hinders their ability to enter solution with aqueous media, such as blood or spinal fluid.

One notable quantum dot encapsulation technique involves utilizing a double fluoroalkyl-ended polyethylene glycol molecule (Rf-PEG) as a surfactant, which will spontaneously form micellular structures at its critical micelle concentration (CMC).

To determine the average diameter, D, of the QDs, the following empirical equation is used: Where It is during encapsulation that the ZnS shell plays an especially important role, in that it helps prevent the agglomeration of CdSe particles that had no shell by occupying the previously mentioned bonds on the dot's surface; however, clumping can still occur through secondary forces that arise from common hydrophobicity.

Generally, two end groups result in the highest conversion into micelles (91%):[8] At molecular weights between 6 and 10 kilodaltons the Rf-PEG hydrogel acts as a Maxwell material, which means the fluid has both viscosity and elasticity.

[9][10] Plotting the first- vs second-order integrals of the modulus values, a Cole-Cole plot is obtained, which, when fitted to a Maxwell model, provides the following relationship: Where Based on the Maxwellian behavior of the hydrogel and observations of erosion via surface plasmon resonance (SPR), the following data results for 3 common Rf-PEG types at their specified concentrations:[11][12] XKCY denotes X thousand daltons of molecular mass and Y carbon atoms.