Applied Research, Water-soluble Semiconductor Quantum Dots In The Cell

The applications of nanomaterials in biological and biomedical fields have become one of the most attractive research fields in recent years. Water-soluble quantum dots (QDs) are a kind a novel bio-labeling material owing to their outstanding optical properties, such as broad absorption and narrow symmetric emission spectra, size effect, high quantum efficiency, high photostability, and etc. This thesis focused on the methods to facilitate the cellular uptake of water-soluble fluorescent quantum dots. The two methods used were peptide modifying for CdTe QDs and cationic polymer packing for Mn:ZnSe QDs (D-dots). The intracellular distribution and optical properties of quantum dots in living cells were investigated by a laser scanning confocal microscope (LSCM) and a micro-PL spectrometer. The main contents are the following:1. As one of the most popular cell-penetrating peptides (CPPs), Tat peptide can facilitate the cellular uptake of diverse biological macromolecules and drugs. In this thesis, Tat peptide was conjugated with CdTe quantum dots to improve the cellular uptake of CdTe quantum dots. The conjugation of Tat peptide to QDs led to a remarkable redshift of the photoluminescence (PL) spectrum of QDs. After cellular uptake of the Tat-QDs conjugates, Tat-QDs were mainly distributed in the lysosomes. The micro-PL spectrum of Tat-QDs in lysosomes showed a spectral blueshift, which was most probably due to the fact that Tat peptide was digested by the enzymes in lysosomes, leaving the Tat-detached QDs in lysosomes. Therefore, the detachment of Tat peptide from QDs can be monitored according to the spectral changes of QDs, which provides the possibilities to design novel methods for delivery and release of targeted drugs.2. Water-soluble D-dots, without heavy metal ions, not only have the outstanding optical characteristics as traditional QDs, but also show extremely low cytotoxicity. Thus, the D-dots have great potential to become a new kind of bio-labeling material. However, the low cellular uptake efficiency of D-dots impedes its application in bio-labeling. Up to now, bio-labeling using D-dots has not been reported. In this thesis, similar to the gene transfection, the cationic polymer was used to pack D-dots in order to improve the cellular uptake of D-dots. This method greatly raised the cellular uptake efficiency of D-dots and is the first step for their cellular application in the future.