The article reviews the use of gold nanoparticles (AuNPs) in chemical and biological sensing. AuNPs are synthesized through various methods, including citrate reduction, Brust-Schiffrin, and place exchange, and can be functionalized with different ligands to enhance their stability and reactivity. They exhibit unique physical and chemical properties, such as size-dependent electronic and optoelectronic properties, surface plasmon resonance (SPR), and fluorescence quenching, which make them suitable for sensing applications. The review discusses the development of AuNP-based sensors for detecting metal ions, organic molecules, proteins, nucleic acids, and microorganisms. These sensors utilize AuNP aggregation, SPR, and fluorescence quenching to provide rapid and sensitive detection. The article also highlights the use of AuNPs in colorimetric sensing, FRET-based detection, molecular beacons, and "chemical nose" approaches, emphasizing their potential in various biomedical, forensic, and environmental applications.The article reviews the use of gold nanoparticles (AuNPs) in chemical and biological sensing. AuNPs are synthesized through various methods, including citrate reduction, Brust-Schiffrin, and place exchange, and can be functionalized with different ligands to enhance their stability and reactivity. They exhibit unique physical and chemical properties, such as size-dependent electronic and optoelectronic properties, surface plasmon resonance (SPR), and fluorescence quenching, which make them suitable for sensing applications. The review discusses the development of AuNP-based sensors for detecting metal ions, organic molecules, proteins, nucleic acids, and microorganisms. These sensors utilize AuNP aggregation, SPR, and fluorescence quenching to provide rapid and sensitive detection. The article also highlights the use of AuNPs in colorimetric sensing, FRET-based detection, molecular beacons, and "chemical nose" approaches, emphasizing their potential in various biomedical, forensic, and environmental applications.