Photoelectrochemical biosensor for protein kinase A detection based on carbon microspheres, peptide functionalized Au-ZIF-8 and TiO2/g-C3N4.

In this work, a novel and sensitive photoelectrochemical (PEC) strategy was designed for protein kinase A (PKA) detection, comprising carbon microsphere (CMS) modified ITO electrode, TiO2 as the phosphate group recognition material and graphite-carbon nitride (g-C3N4) as photoactive material. For the first time, gold nanoparticle decorated zeolitic imidazolate frameworks (Au-ZIF-8) was employed to fabricate biosensor for PKA activity assay with the function of substrate peptide immobilization and signal amplification. Firstly, substrate peptides were assembled on the Au-ZIF-8/CMS/ITO surface through the covalent bonding between the gold nanoparticles (AuNPs) and sulfydryl groups of the peptides. Then, in the presence of ATP, phosphorylation of the substrate peptide was achieved under PKA catalysis. Finally, TiO2-g-C3N4 composites were further modified on the electrode surface based on bonding between TiO2 and phosphate groups created via phosphorylation of the peptide (yielding TiO2-g-C3N4/P-peptide/Au-ZIF-8/CMS/ITO), which is different with our previous work by directly immobilizing g-C3N4 composite on electrode surface. The developed method showed a wide linear range from 0.05-50 U mL-1. The detection limit was 0.02 U mL-1 (S/N = 3). The constructed biosensor exhibited high detection specificity for PKA. In addition, the wide applicability of this biosensor was demonstrated by evaluating the inhibition ability of ellagic acid towards PKA.