Simultaneous Determination of Protein Kinase A and Casein Kinase II by Dual-Color Peptide Biomineralized Metal Nanoclusters.

We design two artificial substrate peptides to synthesize blue-emissive Cu nanoclusters and red-emissive Au nanoclusters, respectively. In addition to the biomineralization function, these two peptides retain the biological activity to be phosphorylated by protein kinase and digested by carboxypeptidase Y. In the absence of protein kinase, the peptides capped on the nanoclusters suffer consecutive exocleavage by carboxypeptidase Y, resulting in oxidation and thus fluorescence quenching of the nanoclusters due to the losing of peptide protection. In the presence of protein kinase A and casein kinase II, the phosphorylation modification on corresponding substrate peptides protects the peptides against carboxypeptidase Y digestion and then the fluorescence of the nanoclusters can be retained. Since a single excitation wavelength can excite the both nanoclusters, blue and red emissive signals can be collected at the same time and then the quantitative determination of protein kinase A and casein kinase II can be achieved simultaneously.