Cell-based ELISA for detection of HER2 and pHER2 using PtV-Chip. a) Schematic mechanism for cell-based ELISA for cell surface biomarker detection using PtV-Chip. Cells were seeded in the assay wells in the bottom plate. Antibody conjugated PtNPs were used to target the cell surface biomarkers and to react with the hydrogen peroxide to produce oxygen gas. b), c) PtV-Chip detection of HER2 expression on 1,000 MDA-MB-231, MCF-7, or SKBR-3 cells. d), e) PtV-Chip detection of pHER2 expression on SKBR-3 and MCF-7 cells treated with or without 100 ng·mL−1 EGF and 5 mM CI-1033. Scale bar, 1 cm for (b) and (d). The error bars in b and d represent the SD of three measurements.