PEGylation of CdSe/ZnS core/shell nanoparticles and its behavior at different pH

Surface modification of CdSe quantum dots (QDs) plays a significant role for their use in biomedical field due to their cytotoxicity effects. CdSe QDs and CdSe/ZnS nanoparticles (NPs) have been prepared by chemical route and their functionalization has been done using Polyethylene glycol diamine (PEGdiamine) polymer. Absorption in the ultra-violet-visible and infra red region confirms the encapsulation of PEGdiamine over CdSe/ZnS NPs. TEM micrographs also show the growth of ZnS over CdSe QDs and PEGylation over CdSe/ZnS NPs. The photoluminescence (PL) spectra in different pH environments ranging pH 2-10 have been deeply investigated to know the stability of NPs. CdSe QDs, CdSe/ZnS NPs and PEGylated CdSe/ZnS NPs agglomerate with complete disappearance of fluorescence peak at low pH (below pH 4) however no shift in the fluorescence emission peak is observed for the pH range 4-10. Therefore NPs can be used as the fluorescence tags for biomedical field in this specific range 6-8 pH. PEGylation leads to increase in the PL intensity as well as shows better stability of CdSe/ZnS NPs. CdSe/ZnS NPs and PEGylated CdSe/ZnS NPs are more luminescent in the weak acidic environment than uncoated CdSe QDs.