Polyacrylamide Gel-Contained Zinc Finger Peptide as the “Lock” and Zinc Ions as the “Key” for Construction of Ultrasensitive Prostate-Specific Antigen SERS Immunosensor

In this work, we adopted polyacrylamide gel-contained zinc finger peptide (PZF) as a "lock" of Raman signal and zinc ions (Zn2+) as a sensitive "key", which was converted from target-captured ZnO NPs, to achieve the measurement of prostate-specific antigen (PSA). Owing to the lock effect from PZF, the surface-enhanced Raman scattering (SERS) tag toluidine blue (TB) connected on Ag NP-coating silica wafer was sheltered leading to low Raman response. Meanwhile, target PSA can specifically connect with antibody 2-coupled ZnO nanocomplexes (ZnO@Au@Ab2) and antibody 1-coupled magnetic (CoFe2O4@Au@Ab1) nanocomposite through sandwich immunoassay. In the presence of HCl, the ZnO NPs would convert into Zn2+ to open the PZF because Zn2+ can specifically react with zinc finger peptide to destroy the PZF structure forming abundant pores. In this way, Zn2+ could act as the key of Raman signal to open the PZF structure obtaining a strong Raman signal of TB. The proposed SERS sensor can have a quantitative detection of PSA within the range of 1 pg mL-1 to 10 ng mL-1 with a detection limit of 0.65 pg mL-1. The interaction between zinc finger peptide and Zn2+ was firstly applied in SERS sensor for the sensitive detection of PSA. These results demonstrated that the new designed SERS biosensor could be a promising tool in biomarker diagnosis.