Spherical gold nanoparticles are widely used in biomedical applications due to their unique optical properties and biocompatibility. They serve as effective agents in drug delivery systems, where they can be functionalized to target specific cells, such as cancer cells, minimizing damage to healthy tissue. In diagnostics, these nanoparticles are employed in colorimetric sensors and lateral flow assays—like in rapid pregnancy and infectious disease tests—because their color changes visibly based on aggregation state. They are also used in photothermal therapy, where they accumulate in tumor tissues and generate heat when exposed to near-infrared light, destroying cancer cells selectively. In imaging, their strong light scattering enhances contrast in techniques such as dark-field microscopy and optical coherence tomography. Additionally, spherical gold nanoparticles act as catalysts in chemical reactions and are integrated into biosensors and electronic devices for improved sensitivity and conductivity.