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. IC50 values of several inhibitors of c-Src determined by the present assay are consistent with reported values.

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► We designed a quite simple assay for detecting the protein kinase activity.
► This assay is based on a substrate peptide-induced coagulation of gold nanorods (NRs).
► The phosphorylation of the substrate by the protein kinase is detected not only as a blue-to-red color changes but also as a highly sensitive change in absorption of the NR dispersion in the near-IR.