KLK3 and posterior cortical atrophy: Herein, this study reports a double‐SERS satellite immunoassay, made of an Au–Ag dealloyed intra‐nanogap nanoflower (Au–Ag DINF) with strong SERS signals and Au magnetic nanoparticles (AuMNPs) with magnetic capture and SERS amplification, for sensing multiple PSA (free PSA (fPSA), complexed PSA (cPSA) and [‐2]proPSA (p2PSA)) toward potential PCa screening.