Now, researchers from Poland and Serbia have developed a faster and cleaner way to make it by using the same natural process that turns a glass of ouzo cloudy when mixed with water.

The “ouzo effect” occurs when alcohol, water and oil combine to form a fine, stable mist of droplets. In ouzo, light scatters on these microscopic droplets, giving the drink its milky appearance.

In the laboratory, this phenomenon uses a mixture of water, alcohol, and oil which spontaneously transforms into a fine, stable mist of droplets. These are ready-made mini-laboratories in which metal particles can be produced.

In a new paper, created in collaboration with colleagues from Serbia, physicists from Poznań and physical chemists from Łódź described using this simple trick to produce gold intended primarily for dermatological and cosmetic applications.

The recipe is surprisingly simple and similar to preparing cocktails at a bar: 12 ml of an alcoholic solution of tea tree oil was slowly added dropwise to 160 ml of a diluted gold solution in aqua regia (a mixture of strong acids capable of dissolving gold). The liquid was stirred, and the “magic” was signalled by a colour change from yellow to red, and a deposit on the walls of the vessel.

An additional short ultrasonic bath prevented the grains from sticking together. Finally, the mixture was rinsed and dried. The entire process ran without heating, external reducing agents, and surfactants (detergents).

Research confirms that this chemical “kitchen” creates pure, crystalline gold particles with a classic structure and smooth surface, each coated in a thin layer of oil. The average particle size was approximately 130–170 nanometers – over a hundred times smaller than the width of a hair, yet large enough to impede deep skin penetration.

In other words, the material naturally acts on the surface, which is desirable in ointments, creams, and balms.

The scientists investigated how human cells would react to the presence of these particles in a standard test.

“At low and medium gold concentrations (up to 500 µg/ml), no significant negative effects were observed; at 1000 µg/ml, a slight change was observed, and only the highest dose (2000 µg/ml) reduced cell survival. In comparison, the so-called positive control – a toxic substance used to verify whether the test detects any harmful effects – reduced survival by approximately 70%. This result indicates that the test itself functioned correctly, and the tested gold was safe at reasonable doses,” they said.

Gold particles are already widely used in diagnostics – for example, in rapid test strips – and in cosmetics, they find their way into creams and serums as a brightening and protective ingredient.

But the researchers’ paper, published in the scientific journal Materials Letters, is the first report of using tea tree oil in the ouzo method for such synthesis.

If this “Greek trick” proves effective in further trials, it could become a practical recipe for industry: quick, inexpensive, and easy to implement on a larger scale.

The natural next step is testing in finished products – on the skin and under real-world conditions – and investigating how such gold particles interact with typical ingredients in creams and lotions.

It is also worth exploring whether the choice of oil or minor changes to the “cocktail” will allow to adjust the size and properties of the particles for specific purposes, such as solutions for sensitive or problematic skin.

PAP - Science in Poland

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