Abstract
Bio-labeling applications of quantum dots (QDs) have grabbed scientists' attention due to their numerous benefits to human life. The quality properties such as strong, narrow, tunable and size-dependent emission of broad absorption spectrum QDs, combined with water-solubility and non-toxicity, are needed for QDs to perform as excellent labeling tools in biological applications. Besides, predictable and reliable controls to achieve perfect and biologically safe QDs with excellent optical properties are expected. In this study, we managed to synthesize cadmium sulfide (CdS) QDs with a mean size of 8 nm by capping it with thioglycolic acid—which has hydrogen bonding—to make QDs soluble in aqueous solutions. Polyethilenimine has functioned to render the QDs to be water soluble and enhances photo-oxidation even in aqueous solution. It also acted as a ligand to modify CdS QDs to prevent surface trap and thus increase CdS QDs' quantum yield. Furthermore, improved stability of the QDs in polymer sphere and non-toxicity is needed. Therefore, the ideal bio-labeling QDs should be dense and equal in size and shape to achieve constant photoluminescence peak. Hence, the CdS QDs have been capsulated with poly(2vinylpyridine) (P2VP) homopolymers and apo-ferritin in order to compare which one is the best capsule for QDs with the desired properties for applications in bio-labeling.
