Gold nanoparticles have been used in biomedical applications for over three centuries, but their unique optical and electronic properties have made them highly relevant in modern biomedicine. This review discusses the design, synthesis, functionalization, and applications of gold nanoparticles in biomedical contexts, highlighting their ability to interact with biological systems to improve patient health. Gold nanotechnology is not merely an enhancement of existing treatments but represents a new "Golden Age" of biomedical nanotechnology. The review covers the synthesis of gold nanoparticles, their size, shape, and surface chemistry, and their diverse applications in diagnostics and therapy. Gold nanoparticles can be tailored to exhibit specific properties, such as enhanced photothermal effects, improved imaging contrast, and targeted drug delivery. The review also discusses the synthesis of various gold nanostructures, including nanorods, nanoshells, nanocages, and nanostars, and their potential in biomedical applications. Functionalization of gold nanoparticles with various ligands and biomolecules allows for targeted delivery and enhanced interaction with biological systems. The review highlights the importance of surface chemistry in determining the biological compatibility and functionality of gold nanoparticles. The review also discusses the use of gold nanoparticles in in vitro diagnostics, including their ability to enhance imaging contrast and facilitate the detection of biomolecules. Overall, gold nanoparticles offer a promising platform for the development of advanced biomedical technologies.Gold nanoparticles have been used in biomedical applications for over three centuries, but their unique optical and electronic properties have made them highly relevant in modern biomedicine. This review discusses the design, synthesis, functionalization, and applications of gold nanoparticles in biomedical contexts, highlighting their ability to interact with biological systems to improve patient health. Gold nanotechnology is not merely an enhancement of existing treatments but represents a new "Golden Age" of biomedical nanotechnology. The review covers the synthesis of gold nanoparticles, their size, shape, and surface chemistry, and their diverse applications in diagnostics and therapy. Gold nanoparticles can be tailored to exhibit specific properties, such as enhanced photothermal effects, improved imaging contrast, and targeted drug delivery. The review also discusses the synthesis of various gold nanostructures, including nanorods, nanoshells, nanocages, and nanostars, and their potential in biomedical applications. Functionalization of gold nanoparticles with various ligands and biomolecules allows for targeted delivery and enhanced interaction with biological systems. The review highlights the importance of surface chemistry in determining the biological compatibility and functionality of gold nanoparticles. The review also discusses the use of gold nanoparticles in in vitro diagnostics, including their ability to enhance imaging contrast and facilitate the detection of biomolecules. Overall, gold nanoparticles offer a promising platform for the development of advanced biomedical technologies.