This study introduces an "endpoint chemistry" one-pot synthesis for highly stable, multi-functionalized gold nanoparticles coated with polyaniline (Au@PANI), which is simpler and more controllable than traditional multi-step methods. The core innovation uses nitrobenzene-type compounds as precursors that undergo a combined reduction and in-situ polymerization to directly form the functional layer on the gold surface. Screening for biological applications focused on phenylboronic acid and galactose variants, which both showed effective accumulation in cancer cells and achieved significant anti-cancer effects via Photodynamic Therapy (PDT) when conjugated with Ce6; notably, the galactose variant also exhibited unique M1-type immune-stimulating properties. The platform integrates dual biomedical functions—diagnosis (using SERS and optical imaging) and was validated in vivo, confirming its capability to effectively inhibit bladder tumor growth. This versatile methodology offers a streamlined framework for functionalizing gold nanoparticles for targeted cancer strategies.