MultiDots consist of several quantum dots within a patented PEG polymer coating. The pegylated fluorescent nanoparticles have very tight size distribution and the amine functional groups on the surface allows conjugation of proteins to label cells of interest. MultiDots with a tighter emission spectrum than current fluorescent reagents, reduces spectral overlap, increases assay sensitivity and eliminates complex spectral compensation. The RPAT4 antibody conjugated to this MultiDot recognizes human CD4, a 55 kDa cell surface glycoprotein that is primarily expressed on a subpopulation of T lymphocytes, on peripheral blood monocytes and on tissue macrophages.