Colloidal gold is a liquid containing tiny gold particles suspended in a fluid, like purified water. These particles are submicroscopic, measuring between 1 and 100 nanometers. The substance has a long history, dating back to the 19th century, and today it holds a position in both advanced scientific research and the alternative health market. Its applications are diverse, ranging from medical diagnostics to unproven dietary supplements.
The Science of Colloidal Gold
Colloidal gold is a type of mixture known as a colloid, where microscopically dispersed insoluble particles are suspended throughout another substance. The synthesis process, often involving the reduction of a gold salt, allows for precise control over the particle size. This control is important, as the size and shape of the gold nanoparticles dictate the liquid’s physical and chemical properties.
Instead of the familiar yellow metallic hue, colloidal gold appears as a vibrant ruby-red liquid. This coloration is not a chemical change but a physical phenomenon called localized surface plasmon resonance. The free electrons on the surface of the gold particles oscillate when they interact with light, causing them to absorb blue-green light and reflect red light.
The specific color can be tuned by altering the nanoparticle’s dimensions. For example, smaller, monodisperse gold nanoparticles around 30 nm in diameter produce the characteristic red color. As the particles increase in size, the resonant wavelength shifts, and the solution can appear purple or even blue.
Applications in Modern Medicine and Technology
The most widespread application of colloidal gold is in lateral flow assays, the technology behind common at-home diagnostic kits like pregnancy tests and rapid COVID-19 tests. In these devices, the gold nanoparticles function as a colorimetric reporter. They are coated with antibodies specific to a target molecule, such as the hCG hormone for pregnancy or a viral antigen.
When a sample like urine or saliva is applied to the test strip, it flows along a membrane. If the target molecule is present, it binds to the antibody-coated gold nanoparticles. This complex migrates until it reaches the test line, which contains more antibodies that capture it. As numerous gold nanoparticle complexes accumulate, their collective red color becomes visible, indicating a positive result.
Beyond diagnostics, gold nanoparticles are used in other scientific fields. In electron microscopy, they are used as a contrast agent to stain and visualize biological structures. Researchers are also investigating their potential for targeted drug delivery, loading nanoparticles with therapeutic agents to guide them directly to tumors.
Use as a Health Supplement
Separate from its role in diagnostics and research, colloidal gold is marketed as a dietary supplement. Proponents claim benefits such as enhancing cognitive function, improving memory, reducing inflammation, alleviating joint pain, and boosting mood.
These claims are linked to anecdotal reports or historical uses of gold in traditional medicine systems. Marketing materials suggest the nanoparticles can improve neural communication or provide anti-inflammatory effects. Products are sold online and in health food stores with suggested dosages and user testimonials.
These claims are not supported by large-scale, rigorous scientific evidence, and mainstream medical organizations do not recognize colloidal gold as an effective treatment for any condition. The proposed mechanisms for how ingesting gold nanoparticles would achieve these health benefits remain unproven. This research is distinct from the evidence available for orally consumed colloidal gold supplements.
Safety and Regulatory Standing
In the United States, the Food and Drug Administration (FDA) has not approved colloidal gold to treat or prevent any disease. The agency has stated that over-the-counter products with colloidal ingredients are not generally recognized as safe and effective. It has also issued warning letters to companies for making unsubstantiated health claims.
There is a lack of long-term studies on the effects of ingesting gold nanoparticles. Research into targeted therapies under medical supervision is very different from the regular consumption of commercial supplements. The quality and concentration of nanoparticles can also vary widely between products, adding to the uncertainty.
A concern with metallic supplements is the risk of argyria, a condition causing irreversible blue-gray skin discoloration. However, argyria is caused by silver particles from colloidal silver products, not gold. While gold is not associated with argyria, this does not confirm its overall safety, as the long-term consequences of gold particle accumulation are not well understood.