Novel photoelectrochemical immunosensor for disease-related protein assisted by hemin/G-quadruplex-based DNAzyme on gold nanoparticles to enhance cathodic photocurrent on p-CuBi2O4 semiconductor

A novel p-type semiconductor material (p-CuBi2O4) is designed for the construction of split-type photoelectrochemical (PEC) immunosensor for alpha-fetoprotein (AFP) with the hemin assistant to enhance the cathodic photocurrent. Initially, the photocathode of PEC immunosensor is fabricated by p-CuBi2O4 on a layer of gold nanoparticles (AuNPs, as a front contact of p-CuBi2O4) to enhance the efficiency of charge separation. In the presence of target AFP, a sandwich-type immunoreaction was carried out in capture antibody-coated microplate by using detection antibody and hemin-based G-quadruplex (labeled on the AuNP) as the signal probe. Upon exonuclease I (Exo I) introduction, the enzyme digested the hemin/G-quadruplex-based DNAzyme to release the hemin[Fe(III)], which captured the generated electrons of p-CuBi2O4-based photocathode to enhance photocurrent via the reduction of hemin[Fe(III)] to hemin[Fe(II)] in PEC detection system. Under the optimal conditions, the split-type photocathodic immunosensor showed a wide linear dynamic range from 50 pg mL−1 to 20 ng mL−1 at a limit of detection (LOD) of 14.7 pg mL−1 toward target AFP. Moreover, the PEC immunosensor also displayed high specificity and good reproducibility. Favorably, method accuracy was evaluated to analyze human serum specimens, and gave matched-well results in comparison with commercially available enzyme-linked immunosorbent assay (ELISA) method.