A highly sensitive electrochemiluminescence assay for protein kinase based on double-quenching of graphene quantum dots by G-quadruplex-hemin and gold nanoparticles

A highly sensitive electrochemiluminescence (ECL) strategy was developed for the protein kinase A (PKA) activity and inhibition assay based on double-quenching of graphene quantum dots (GQDs) ECL by G-quadruplex-hemin DNAzyme and gold nanoparticles (AuNPs). In this strategy, the GQDs were modified onto the indium-tin oxide (ITO) electrode and further assembled with substrate peptide of target protein kinase through covalent coupling, which can exhibit high and stable ECL signal. The AuNPs, functionalized with the phosphorylated DNA and G-quadruplex-hemin DNAzyme via Au-S chemistry, were selected as quenching probes. In the presence of PKA, the peptide on the electrode was phosphorylated and the AuNPs functionalized with the phosphorylated DNA and G-quadruplex-hemin DNAzyme were subsequently integrated onto the phosphorylated peptide by Zr4+. Owing to the reduction of coreactant H2O2 resulting from G-quadruplex-hemin DNAzyme catalytic reaction and the ECL energy transfer (ECL-RET) between AuNPs and GQDs, the ECL intensity of GQDs was significantly decreased. By taking advantage of the double-quenching effect, this assay can detect PKA with a linear range of 0.05 to 5 U mL−1 and a detection limit of 0.04 U mL−1. In addition, the PKA inhibition assay and interferences experiments of CK2 and T4 PNK have been studied respectively. This assay was also successfully applied to PKA assay in serum samples and cell lysates, indicating that the developed method have the potential applications in protein kinase-related biochemical fundamental research and clinical diagnosis.