Fluorescent detection of protein kinase based on positively charged gold nanoparticles

Herein, we report a fluorometric method for monitoring the activity and inhibition of protein kinase based on positively charged gold nanoparticles, (+)AuNPs. In this assay, when the cationic substrate peptide (S-peptide) is phosphorylated by protein kinase, the resulting negatively charged product peptide (P-peptide) will be adsorbed onto (+)AuNPs through electrostatic interaction, and the fluorescence of fluorescein isothiocyanate (FITC) on the peptide will be quenched by (+)AuNPs. Thus, the fluorescence of solution can respond to the activity of protein kinase. The feasibility of this (+)AuNPs-based method has been demonstrated by sensitive measurement of the activity of cAMP-dependent protein kinase (PKA) with a low detection limit (0.5 mU μL−1). Furthermore, the system is successfully applied to estimate the IC50 value of PKA inhibitor H-89. The fast mix-and-readout detection process as well as the simple synthesis of the unmodified (+)AuNPs makes this proposed method a promising candidate for simple and cost-effective kinase activity detection and a good potential in high-throughput screening of kinase-related drugs.