ESR1 and cancer: Metalnanoparticles are commonly used in cancer as drug delivery,61,62 photothermal,63,64 and imaging agents.65−67 Here, we demonstrate that the multiplexing capabilities of SERScombined with targeted anti-ERα antibody-functionalized (ERα-AuNPs)and nontargeted anti-HER2 antibody-functionalized (HER2-AuNPs) nanotagscan be successfully used to understand more about nanoparticle uptakein tumor spheroids with the advantages of high sensitivity and specificity.The results showed that SERS can provide a sensitive method for theanalysis of 3D tumor models grown in microfluidic chips.