Every living organism on earth owes its viability to its different sizes of nanostructures and the interaction of these structures at the nano size. Nanotechnology gives us an opportunity to understand nanoscale processes in living organisms and interfere with and manipulate them. Today, biocompatible nanosized structures are designed by applying developments in nanotechnology to biomedicine; thus, therapeutic agents are available to reach diseased tissues and even cells. However, it is essential that nanomaterials that would be used for therapeutic aims be targetable to diseased areas and have low toxicity. In addition, these nanomaterials must have high biocirculation and pharmacokinetic properties. Compared to conventional methods, gold nanoparticles (AuNPs) have the appropriate physical, chemical, mechanical, optical, and electronic properties for the design of nanobiomaterials that exhibit high selectivity, specificity, and sensitivity in the early detection, diagnosis, and treatment of diseases. Recently, gold has been used in prominent drug and gene carrier platforms because it binds various therapeutic agents and biomolecules in a stable way to create biocompatible complex structures. In addition, it has nontoxic nuclei and surface properties such as charge and hydrophobicity, which are adjustable in a monolayer. In the near infrared region, AuNPs are effective probes for in vivo and in vitro imaging with their high plasmon resonance absorption and scattering. In addition, their ability to rapidly convert optical energy to heat energy enables the ablation of invasive cancer tissues photothermally, even at a low power. This review sheds light on the synthesis, surface functionality, and potential applications of colloidal AuNPs in biomedicine.