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 HI30 antibody conjugated to this MultiDot reacts with human CD45, one of the most abundant hematopoietic markers and one that is expressed on all leukocytes (the Leukocyte Common Antigen, LCA). CD45 is a protein tyrosine phosphatase existing in several isoforms, each being generated and expressed in cell-specific patterns. With its broad cell distribution, CD45 is critical for many leukocyte functions, regulating signal transduction and cell activation associated with the T cell receptor, B cell receptor, and IL-2 receptor. Other forms of CD45, with restricted cellular expression, include CD45R (B220), CD45RA, CD45RB, CD45RO and others.