The prepared unlabeled electrochemical immunosensor (EI) can sensitively detect prostate-specific antigen (PSA) in a wide linear range (0.1–1000 ng/mL) (Figure 3d), with a detection limit as low as 0.051 ng/mL, and could have broad application potential in the clinical diagnosis of prostate cancer. This evidence concerns the gene KLK3 and prostate carcinoma.