A colorimetric assay of protein kinase activity based on peptide-induced coagulation of gold nanorods

We succeeded in applying gold nanorods (NRs) for the detection of protein kinase (PK) activity based on a substrate-induced coagulation mechanism. Because NRs have cationic surface charges due to surface-adsorbed cetyltrimethylammonium bromide, phosphorylated substrate peptides, which gain augmented anionic charges by phosphorylation, induce coagulation of the NRs, resulting in a red-to-blue color change of the corresponding NR dispersion. A large absorption coefficient of the NRs at the near-IR region enabled clear-cut detection of the peptide-induced coagulation. IC(50) values of several inhibitors of c-Src determined by the present assay are consistent with reported values.