The silica-coated superparamagnetic nanoparticles with the uniform diameter of about 60 nm were synthesized-by reverse microemulsions method. And the magnetic nanoparticles were modified with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS). The immunomagnetic nanoparticles were then successfully prepared by covalently immobilizing anti-CD34(+) monoclonal antibodies to the surface of amino silane modified magnetic particles. The cell separation results showed that the synthesized immunomagnetic nanoparticles could rapidly and conveniently separate the CD34(+) cells with high efficiency and specificity than normal ones. The surface morphology of separated target cells was examined by scanning electron microscope (SEM). Atomic force microscope (AFM) also characterized the magnetic materials on the surface of the separated target cells for the first time, which further confirmed that the target cells were separated by the immunomagnetic nanoparticles. The viability of the separated cells was studied by culturing method and Beckman Vi-cell viability analyst. Therefore, our experiments provided a new, direct, rapid mode to separate target cells. (c) 2006 Elsevier B.V. All rights reserved.