CdSe core nanoparticles were synthesized from the stearate complex of Cd and Se powder in octadecene solution containing organic stabilizers. After purification, CdS inorganic shell was made on CdSe core to yield CdSe/CdS core/shell nanostructure using successive ion layer adsorption and reaction method. The outmost half layer of the inorganic CdS shell was designed to be cadmium ion layer. Then, the hydrophobic CdSe/CdS was converted to hydrophilic CdSe/CdS-AET by treating with aminoethanethiol (AET). The cadmium half layer on CdSe/CdS surface was an excellent promoter for the covalent conjugation of CdSe/CdS to thiolate of AET. Finally, CdSe/CdS-AET was bioconjugated to a PEG analogue, poly(ethylene glycol) monomethyl ether mono(succinimidyl succinate) ester. The advantage of using AET compared to mercaptopropionic acid was the stabilization of Cd-thiolate bond during the following bioconjugation process. Investigations of semiconductor nanoparticles with different surface materials are discussed using transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis), photoluminescence (PL), and Fourier transformed-infrared (FT-IR) spectroscopy.