Herein, nanogap amplified plasmonic heat-generators are fabricated by decorating Pt nanodots on gold nanospheres (GNSs@Pt@mPEG) by maintaining strategic nano-gaps (1-2 nm) and studied precisely for plasmonic photothermal therapy (PPTT) of colon cancer by passive tumor targeting. The surface modification of GNSs@Pt with poly(ethylene glycol) methyl ether thiol (mPEG) increases their accumulation in tumor cells and hence the GNSs@Pt@mPEG stay at the tumor site for a longer time. The nanogap amplified GNSs@Pt@mPEG (O.D. = 4.0) generated high plasmonic photothermal hyperthermia and utilized a low NIR power density (0.36 W cm-2) for the elimination of tumor cells in only 150 s of irradiation time and shows excellent colloidal and photo-stability. The predominant distribution of GNSs@Pt@mPEG caused effective tumor cell death and promoted uniform treatment on tumor sites. In vivo studies demonstrated that the GNSs@Pt@mPEG have very low toxicity, high biocompatibility, and thermal stability, stay longer at the tumor site, induce tumor cell death without side effects, and show significantly less uptake in other organs except for the spleen. The significant accumulations and longer stay suggested that they are favorable for tumor passive uptake and the possibility of enhanced PPTT after intravenous administration. The nano-particles were stable up to O.D. 200 and have at least 12 months shelf-life without losing colloidal stability or photothermal efficacy. These findings lay the groundwork for using GNSs@Pt@mPEG as a NIR light-responsive PPTT agent and demonstrated their potential for further use in clinical applications.