Utilized in biosensors for detecting DNA, proteins, and pathogens with ultra-high sensitivity, surface-enhanced Raman spectroscopy (SERS) for single-molecule detection and chemical analysis, photothermal therapy for selective tumor ablation using near-infrared light, lateral flow immunoassays for rapid diagnostic tests (e.g., COVID-19, pregnancy tests), drug delivery carriers with triggered release mechanisms, catalysts for CO oxidation and selective hydrogenation, conductive inks for printed electronics and flexible circuits, colorimetric sensors for heavy metal detection in water, labeling agents for electron microscopy in biological imaging, and optical coatings with tunable surface plasmon resonance. Gold nanoparticles offer exceptional biocompatibility, chemical stability, and unique optical properties for biomedical and sensing applications.