Stable aqueous dispersions consisting of CdS nanoparticles having modal diameters, ranging between 2 and 8 nm, were prepared with amino-derivatized polysaccharides (aminodextrans, hence abbreviated as Amdex) as the stabilizing agents. The size, stability, and luminescence intensity of such dispersions were shown to be dependent on the types of the cadmium salts and aminodextrans used, as well as on the reactant concentrations. Specifically, it was demonstrated that the degree of substitution of amino groups in the aminodextran molecules greatly affected the properties of the dispersions; i.e., with higher degree of substitution, smaller CdS particles and higher luminescence intensity were achieved. It was also shown that the Amdex-CdS nanoparticle complexes could be activated and conjugated with antibody by conventional means. Molecular weight ranges of the Amdex and their complexes with CdS nanoparticles and the purity of antibody-Amdex-CdS nanoparticle conjugates were determined by polyacrylamide gel electrophoresis combined with Coomassie blue staining of resultant gel bands. The purified conjugate of the aminodextran-CdS nanoparticle complex with anti-CD4 monoclonal antibody was mixed with a whole blood control, followed by indirect sheep antimouse antibody-phycoerythrin (SAM-PE) labeling of washed cells incubated with T4-5X-Amdex-CdS. Red blood cells were then lysed and quenched, and the resulting mixture, which was run on a flow cytometer with 488.0 nm argon ion laser excitation, suggested that the T4 antibody from the conjugate was present specifically on lymphocytes.