An immunoconjugate comprised of the recombinant chimeric monoclonal antibody cetuximab conjugated to the N-hydroxysuccinamide (NHS) ester form of the near-infrared (NIR) fluorescent dye IRDye 800CW (cetuximab-IRDye 800) with potential imaging use. The antibody moiety of cetuximab-IRDye 800 binds to the extracellular domain of the epidermal growth factor receptor (EGFR). Upon binding, IRDye 800 may be detected using NIR imaging, which facilitates the visualization and quantification of EGFR-expressing tumor cells. EGFR is a receptor tyrosine kinase that may be overexpressed on the cell surfaces of various tumor types.