What Is Colloidal Gold? | Nanoparticle Suspension Explained

For the full breakdown, see our best Colloidal Gold guide.

Colloidal gold consists of tiny gold particles measured in nanometers suspended in a liquid, usually water, where they stay dispersed rather than settling out. The specific properties of this material depend on particle size, shape, and surface chemistry, which also determine its color and behavior. It is not dissolved gold or a gold salt—it is elemental gold in nanoparticle form.

What Exactly Is Colloidal Gold?

Colloidal gold, also called nanogold, is a colloidal suspension of gold nanoparticles in a fluid. The particles typically range between 1 and 100 nanometers in size, with common lab preparations falling in the 2-to-40-nanometer range. Because the particles are so small, they remain suspended rather than settling to the bottom.

The suspension’s color depends on particle size. Particles smaller than 100 nanometers produce a red or wine-red liquid. Larger particles may appear blue-purple or darker, with some sources also noting yellowish tones for certain sizes. This color variation comes from how the nanoparticles interact with light—a property that shifts with even small changes in particle dimensions.

To make colloidal gold, a gold compound called chloroauric acid is reduced using a reducing agent such as sodium citrate, citrate, ascorbic acid, or tannic acid. The type and concentration of the reducing agent control the final particle size. The resulting nanoparticles stay stable in the liquid through electrostatic repulsion, which prevents clumping.

Applications of Colloidal Gold

Most of the well-documented uses for colloidal gold are in biomedical research and diagnostics. It has served as an electron-dense receptor probe in microscopy, in immunodiagnostic tests, and as a tumor-therapeutic vector in experimental research. Gold colloidal nanospheres were initially developed as imaging agents and later explored in hyperthermia research, where heat from nanoparticles is used to target cells.

In cosmetics, some formulations include colloidal gold for antimicrobial, antifungal, and skin-conditioning purposes. Initial research has not flagged safety concerns for topical use, and skin permeation studies have found spherical gold particles non-toxic to human skin cells. Some wellness supplement products market colloidal gold for cognition, mood, or anti-aging benefits, though these claims are not established by higher-quality scientific sources.

Safety Considerations

Safety depends on how colloidal gold is used and how it enters the body. For topical use in cosmetics, available research has not identified significant safety concerns, though the ingredient has not been formally assessed by the Cosmetics Ingredient Review Expert Panel. Skin permeation studies suggest spherical gold particles are non-toxic to human skin cells.

For ingested wellness use, the evidence is limited. Some sources advise caution because safety data for nanoparticles is still incomplete. Because colloidal gold is a nanomaterial, its properties vary with particle size, shape, and surface chemistry, which means effects can differ between preparations.

Colloidal gold should not be confused with dissolved gold or ionic gold salts, which have different chemical properties and safety profiles. The term refers specifically to a particle suspension, not a solution of gold compounds.