Peptide-conjugated hemin/G-quadruplex as a versatile probe for "signal-on" electrochemical peptide biosensor

In this work, a novel "signal-on" electrochemical peptide biosensor based on peptide-conjugated hemin/G-quadruplex (DNAzyme-peptide) hybrid and rosebud-like MoSe₂@reduced graphene oxide (MoSe₂@rGO) nanocomposite, was developed for detection of prostate-specific antigen (PSA). Interestingly, the peptide not only served as recognition probe to detect PSA, but also acted as the enhancer to improve the enzyme activity of hemin/G4, which promoted the detection sensitivity. Up addition of PSA, Fe₃O₄-labeled DNAzyme-peptide probe was cleaved, followed by the magnetic separation. The cleaved DNAzyme-peptide was then captured onto the cysteine-modified electrode via the interaction between carboxyl groups of peptide and amino group of cysteine. A strong electrochemical signal was obtained from hemin and further was amplified by the enhanced electrocatalysis of DNAzyme-peptide. Compared to the original DNAzyme, DNAzyme-peptide exhibited more than 3-fold enhancement in signal amplification. And MoSe₂@rGO amplified the electrochemical signal due to its good conductivity and large surface area. So the proposed strategy detected PSA down to 0.3 fg/mL, and it showed the advantages of simplicity, low cost by avoiding the use of expensive protein enzyme and additional electroactive species. Therefore, the proposed biosensor potentially provided a very effective tool for early diagnosis of cancer by the detection of PSA.