Gold and platinum bimetallic nanoparticles, Au@PtNPs, have gained attention due to their plasmonic properties. The controlled synthesis of Au@PtNPs involves complex parameters, and the resulting synergy between Au and Pt introduces possibilities for tailoring their properties. This study explores the effects of key-parameters of synthesis (gold core diameters, reaction time, and Pt concentration) on the final properties of Au@PtNPs. Gold nanoparticles of varying diameters were synthesized and used as cores for the reduction of hexachloroplatinic acid, forming a surrounding shell of Pt nanoparticles. The parameters were systematically tuned to understand their impact on morphology, dimension, stability, and plasmonic properties of Au@PtNPs. Increasing Pt precursor concentration resulted in thicker and denser Pt shells, broadening the localized surface plasmon resonance (LSPR) band and improving Au@PtNPs stability. These properties are essential for applications such as photothermal treatment. The synthesis achieved satisfactory products within just 1 h of Pt4+ reduction at mild temperature without using surfactants. Only limited changes in plasmonic properties were observed after 4 h of synthesis, suggesting an optimal reaction period. Manipulating Au core diameter provided LSPR band control, with smaller cores exhibiting greater broadening towards the infrared region. This systematic exploration provided valuable insights for understanding key-parameters governing the synthesis and properties of Au@PtNPs.

Combining direct targeting, enhanced cellular uptake, photothermal transduction capacity, and biocompatibility in the same system is a challenge to make the application of nanoparticles in biomedicine real. This study involves the functionalization of gold nanoparticles (AuNPs) in a few steps with strategic macromolecules to provide characteristics that are key to theragnostic agents. Polyethylene glycol (PEG) is hydrophilic and can improve nanoparticle stability and circulation lifetime. Polylactic acid (PLA) is a biodegradable hydrophobic polymer important to guarantee the interaction and uptake through the cellular membranes. Folate provides specific targeting because tumors usually overexpress folate receptor proteins. Single, double, and triple functionalization of spherical and rodlike AuNPs with these ligands provided different aggregation, stability, and plasmonic properties. Triple functionalization ensured simultaneous nanoparticle stability in an aqueous medium and enhanced cellular uptake. Infrared irradiation increased the temperature of gold nanorods more than of gold nanospheres due to the longitudinal surface plasmon resonance band. The results suggest that this functionalization strategy can be used to tune the desired properties for applications of gold nanoparticles, such as imaging and photothermal therapy in biomedicine research.