This study reports the development and validation of a novel optical biosensor for the early detection of total prostate-specific antigen (tPSA) in serum samples from prostate cancer patients, utilizing a terbium-anthracene-9-carboxaldehyde (Tb-A9C) complex embedded within an epoxy-functionalized carboxymethyl cellulose (CMC) polymer thin film. The gene discussed is KLK3; the disease is prostate cancer.