ABSTRACT
Colloidal semiconductor nanocrystals, or quantum dots (QDs), are inorganic semiconductor nanocrystals with sizes of a few nanometers (Alivisatos 1996; Schmidt 2006). The unique optical properties of these nanoparticles (NPs) brought researchers to exploit them in many biomedical fields, from labeling and imaging to detection and sensoring, as well as gene and drug delivery. The huge interest in QDs is due to their peculiar optical properties, their relatively cheap cost of fabrication, and the easy functionalization of their surfaces for bioconjugation. There is a great interest in trying to develop better synthetic strategies able to yield new nanocrystals with a precise control over shape and composition, from which the optical properties depend. Colloidal synthesis is able to give the best results from this point of view, also with great control over monodispersity (Ozin and Arsenault 2005). Still, nanocrystals synthesized in organic solvents have to be transferred into aqueous solvents before being exploited for biological applications. In fact, biomedicine is a field where semiconductor nanocrystals, and QDs in particular, are being employed the most, substituting more traditional organic dyes (Doshi and Mitragotri 2009; Kim and Dobson 2009; Peteiro-Cattelle et al. 2009).
