Obtaining bimetallic nanoparticles involves synthesis parameters that, when controlled, enhance the physicochemical properties of the nanoparticles, thus broadening their applications. In this context, bimetallic gold and platinum nanoparticles have shown great potential for applications in several scientific fields due to the adjustment of optical properties induced by the synergy of the two metals. Although bimetallic gold and platinum nanoparticles can be obtained in a single step, a two-step synthesis route was used in this work to control one of the essential parameters involved in the synthesis: the gold core (AuNPs). Additionally, platinum in the form of chloroplatinic acid (H2PtCl6 . 6H2O) was chosen as the precursor to evaluate its effects and influence on the formation of bimetallic gold and platinum nanoparticles at different Pt/Au molar ratios. Parameters such as synthesis time, temperature, and stabilizer were also evaluated. To characterize the bimetallic gold and platinum nanoparticles, the following characterization techniques were used: UV-vis spectroscopy, DLS, zeta potential, TEM and TEM/ED. Based on the results obtained, correlations were made between the effects of the parameters and the physicochemical properties exhibited by bimetallic gold and platinum nanoparticles. By varying the concentration of the Pt precursor, it was observed that the shell formed by PtNPs became denser, which resulted in changes in the optical profiles of the bimetallic gold and platinum nanoparticles. Furthermore, the AuNPs plasmon resonance band (LSPR) broadened to longer wavelengths as the Pt/Au molar ratio increased, thereby increasing the stability of bimetallic gold and platinum nanoparticles. Understanding the correlation between the effect of increasing the density of the PtNPs shell and the broadening of the LSPR band of AuNPs enhances the applications of bimetallic gold and platinum nanoparticles in photothermal treatments. The bimetallic gold and platinum nanoparticles were formed in 1 h of synthesis, and after 4 h, subtle changes in optical properties were observed, suggesting the optimal reaction time. The syntheses were carried out at a temperature of 30 degrees C, and an increase of 10 degrees C did not result any changes in the optical properties of the bimetallic gold and platinum nanoparticles. Moreover, all syntheses were conducted without the use of surfactants, and the evaluation of the effect of stabilizers such as sodium citrate and citric acid did not show significant changes in the physicochemical properties of Au@PtNPs. Regarding gold cores, the broadening of the LSPR band to longer wavelengths can be controlled by varying the size of the AuNPs. The 7 nm diameter core was most affected by the Pt concentration in terms of changes in the plasmonic profile, while the 25 and 32 nm cores showed more controlled LSPR band broadening. This study systematically correlated synthesis parameters with the final properties of bimetallic gold and platinum nanoparticles, providing a greater understanding of the influence of these parameters when controlled, enhancing their potential for biomedical treatments.