SYNTHESIS OF POLYSTYRENE ENCAPSULATED ZnS-COATED CdSe NANOCOMPOSITES MODIFIED WITH PLL–PEI–PEG–FA

Current cell tags using dyes lose their luminescence quickly and are not suitable for optical barcoding. Semiconductor quantum dots (QDs), on the other hand, can be engineered to emit different wavelengths, thus permitting tagging of various cells at the same time. Core/shell luminescent quantum dots, cadmium selenide (CdSe) and zinc sulphide (ZnS), were synthesized and incorporated into polystyrene (PS) particles grafted with carboxyl groups using microemulsion polymerization method. Highly luminescent monodispersed PS particles with diameters from 30 nm to 50 nm were chosen for subsequent surface modification. Two series of surface modifications were carried out with PS particles. One was modified with poly(L-Lysine) (PLL), polyethylenimine (PEI), Poly(Ethylene Glycol) (PEG) and folic acid (FA) side chains in sequence through chemical bonding. Another was conjugated with PEG and FA in sequence. The folic acid side chains can enter target cells via folate receptors and assisted in the uptake of the luminescent particles into the cells. This property allows them to be used as fluorescent labels for marking their ingress into cells and also for a cornucopia of biomedical applications.