Likewise, El-Sayed et al. used GNPs for diagnostic applications of cancer cells.81 They observed that anti-epidermal growth factor receptor (anti-EGFR) monoclonal antibody grafted GNPs specifically bind to cancerous cells with greater affinity than non-cancerous cells without any aggregation.264 SPR signals of anti-EGFR–GNPs appeared at 536 nm, when attached to cancerous cells. Here, EGFR is linked to cancer.