Gold nanoparticles (AuNPs) are important components in biomedical applications, particularly in diagnostics and therapeutics. This review discusses the synthesis, properties, and conjugation strategies of spherical AuNPs, as well as their applications in bionanotechnology. AuNPs are synthesized using various methods, including solution-based approaches that control size, shape, and surface functionality. The Turkevich method produces spherical AuNPs with diameters of 10–20 nm, while the Brust method allows for the synthesis of smaller, more stable AuNPs. These nanoparticles possess unique optical and electronic properties, such as surface plasmon resonance (SPR), which enable them to be used in sensing and imaging applications. AuNPs can also quench fluorescence through mechanisms like fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET). In bionanotechnology, AuNPs are used for sensing, where they are conjugated with recognition moieties such as antibodies or aptamers to detect target biomolecules. For example, the "bio-barcode assay" uses AuNPs to detect proteins and nucleic acids with high sensitivity. AuNPs are also used in imaging, where they serve as contrast agents in computed tomography (CT) and other imaging techniques. Additionally, AuNPs are employed in therapeutics, where they can deliver drugs and genes to cells through passive or active targeting mechanisms. Their high surface area allows for the efficient loading and release of therapeutic agents, making them valuable for drug delivery and gene therapy. AuNPs are also used in imaging techniques such as surface-enhanced Raman scattering (SERS) and photothermal imaging. Their ability to be functionalized with various ligands enables them to be used in a wide range of applications, including sensing, imaging, and therapy. The versatility of AuNPs, combined with their biocompatibility and low toxicity, makes them promising materials for future biomedical applications.Gold nanoparticles (AuNPs) are important components in biomedical applications, particularly in diagnostics and therapeutics. This review discusses the synthesis, properties, and conjugation strategies of spherical AuNPs, as well as their applications in bionanotechnology. AuNPs are synthesized using various methods, including solution-based approaches that control size, shape, and surface functionality. The Turkevich method produces spherical AuNPs with diameters of 10–20 nm, while the Brust method allows for the synthesis of smaller, more stable AuNPs. These nanoparticles possess unique optical and electronic properties, such as surface plasmon resonance (SPR), which enable them to be used in sensing and imaging applications. AuNPs can also quench fluorescence through mechanisms like fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET). In bionanotechnology, AuNPs are used for sensing, where they are conjugated with recognition moieties such as antibodies or aptamers to detect target biomolecules. For example, the "bio-barcode assay" uses AuNPs to detect proteins and nucleic acids with high sensitivity. AuNPs are also used in imaging, where they serve as contrast agents in computed tomography (CT) and other imaging techniques. Additionally, AuNPs are employed in therapeutics, where they can deliver drugs and genes to cells through passive or active targeting mechanisms. Their high surface area allows for the efficient loading and release of therapeutic agents, making them valuable for drug delivery and gene therapy. AuNPs are also used in imaging techniques such as surface-enhanced Raman scattering (SERS) and photothermal imaging. Their ability to be functionalized with various ligands enables them to be used in a wide range of applications, including sensing, imaging, and therapy. The versatility of AuNPs, combined with their biocompatibility and low toxicity, makes them promising materials for future biomedical applications.