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Amphiphilic Polysaccharides Used for Quantum Dots Encapsulation

Ching-An Peng, Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan and Morris Hsu, Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan.

Colloidal nanocrystal QDs consisting of an inorganic core/shell structure (e.g., CdSe/ZnS) surrounded by a layer of organic ligands (i.e., TOPO) can be converted into hydrophilic nanoparticles by several approaches. The commonly used strategy is based on the exchange of the original organic layer with hydrophilic ligands, however the physical properties (i.e., quantum yield) are usually deteriorated through such surface modification. In this study, we demonstrated the first time that amphiphilic polysaccharides (alginate and chitosan) can encapsulate CdSe/ZnS by intercalating polysaccharide surfactant's hydrophobic pendant moieties (i.e., octyl chains) into the hydrophobic surfactant layer (i.e., TOPO) on the QD surface, thereby resulting in the phase transfer of hydrophobic QDs from organic solvents to aqueous solution via hydrophilic backbone (i.e., polysaccharides). The average size of water-soluble QDs encapsulated by polysaccharide surfactants was determined by DLS and TEM to be the range of 10-30 nm. As long as the number of pendant groups is sufficient high, the linkage of amphiphilic polysaccharide to the QD surface could be very stable and thereby lead to the physical properties of QD intact. The absorption and emission spectra of QD encapsulated with amphiphilic polysaccharide revealed higher absorbance between 525 and 550 nm and strong photoluminescence with the emission wavelength peaked at 534 nm after excited by UV-light. These fabricated nanomaterials were incubated with several cell lines and showed good biocompatibility.