Quantum dots (QDs) provide many advantageous features that include high quantum yield, broad absorption spectra, large achievable Stokes shifts, narrow symmetric, size tunable emission spectra, and exceptional resistance to photo- and chemical degradation, making them attractive reagents for the long-term visualization of cellular structures and processes. See references 1-4.
The methods employed to date for the intracellular delivery of QDs or other nanoparticles (NPs) can be grouped into three generalized categories based on their physicochemical nature. Passive delivery is a nonspecific process that relies on the inherent physicochemical properties of the QD (surface charge and/or functionalization) to mediate uptake.
Facilitated delivery utilizes a delivery agent (e.g., a cationic peptide or a polymer) that is covalently attached to or electrostatically complexed with the QDs to specifically induce internalization. Both these techniques, while noninvasive, typically utilize the endocytic pathway which results in encapsulation of the QDs within intracellular endolysosomal vesicles and thus requires further strategies to liberate the sequestered QDs to the cytosol if that is ultimately desired. Examples methods of facilitated delivery include using additional chemicals such as sucrose or chloroquine or adding polymers such as polyethyleneimine during delivery to disrupt the endosomes by osmotic shock: such methods are generally quite toxic. Lastly, active delivery methods such as electroporation and microinjection deliver QDs directly to the cytosol through physical manipulation of the cell. However, these are highly invasive techniques that can often compromise the integrity of cellular structures and substantially reduce cellular viability (see reference 10). Thus, each of the previously described methods for delivery of nanoparticles (including quantum dots) is deficient in some way.
Described herein are improvements in intracellular delivery of nanoparticles.