Intracellular uptake of CdSe-ZnS/polystyrene nanobeads

The ideal optical properties of quantum dots (QDs) offer the possibility of using them as fluorescent probes in biological staining and diagnostics. Some techniques have been developed to incorporate QDs into polymer beads, to solve the problems relating to QDs' surface chemistry, such as water solubility, biocompatibility, chemical stability in physiological media, and so on, or to pack different combinations of QDs and produce QD encoded polymer beads. However, the QD encoded polymer beads that have been reported so far are above 100 nm; therefore they are very useful for multiplexed bioassays, but not suitable for staining or labeling of subcellular components or intracellular measurements because of the relatively big size of the beads. There is great need for QD encoded polymer beads smaller than 100 nm. In this work, luminescent CdSe-ZnS QDs were incorporated into polystyrene (PS) beads grafted with carboxyl groups with the use of an emulsion polymerization method, and separation of nanoscale QD encoded PS beads (30 nm) was performed through centrifugation at high speed in viscous solution. The nanobeads were further surface modified with folic acid and their intracellular delivery into NIH-3T3 and HT-29 cell lines was investigated with the use of confocal microscope. The longevity of QDs allows the intracellular delivery of the nanobeads to be tracked over a certain time period.