Figure 7.

Delivery of QD probes inside cells represents a challenge for labeling intracellular targets. Different modes of delivery are being developed to overcome this issue. A) Mechano-chemical modes of QD delivery involve utilization of mechanically strong materials capable of puncturing cell membrane and reaching into intracellular compartments. Delivery using nanoneedle (left) involves attachment of QDs on the outer surface of a stiff nanotube and manual manipulation of the needle on the cell-by-cell basis [37], while delivery platform based on nanosyringes (right) utilizes arrays of hollow vertically aligned nanotubes that enable intracellular release of QD probes upon cell growth on top of these arrays [38]. B) Encapsulation of QD probes within materials capable of endosomal escape represents a promising high-throughput technique for intracellular QD delivery. A general approach involves coating of QDs with materials possessing proton sponge functionality or other means of destabilizing endosome membrane and functionalizing the surface with targeting ligand. Once ligand binds to a receptor on the cell surface, nanoparticles are uptaken by endocytosis. Decrease in pH inside the endosome causes physical changes in QD coating (usually in surface charge), which triggers mechanisms for cytosolic release of QDs and enables targeting of intracellular components [40].