Colloidal gold

As colloidal gold is referred to Sole ( colloids) or gels of tiny gold particles with a diameter of 2 to 100 nm characteristic of colloidal gold is the deep red color that comes through the small gold particle size about.

Production

By reduction of Tetrachloridogoldsäure H [ AuCl4 ] in boiling aqueous solution with citric acid or in ethereal solution with white phosphorus is obtained unstable gold colloids that coagulate easily. Therefore stabilizers, for example citrates and / or detergents such as Tween 20 from be added to such stabilized sols can be gold colloids was precipitated by addition of ethanol.

Physical Properties

When gold colloids, the plasmon oscillation can be observed, ie the collective oscillation of the electrons gold against the gold atom hulls. The wavelength of this light absorbed depends on the particle size and particle density: the larger and closer together the particles are, the greater the absorbed wavelength. The density is critical, as it may lead to induced dipole interaction between the gold particles.

That's why gold colloids are much more colorful than a compact gold bullion.

Use

Gold colloids are used to red coloration of glasses, aggregated gold colloids gild porcelain and glasses.

In biochemistry, colloidal gold is used for the labeling of proteins, for example for the direct dyeing of Western blots. Advantage of the coloring is their high sensitivity and ease of implementation. The disadvantage is that a subsequent immune detection is no longer possible and the coloring only under rather harsh conditions decolorized again ( made ​​invisible ) can be.

In addition to the gold-labeled antibody may be used electron microscopy. Antibody selected areas of the sample fall on the electron-dense gold particles. Furthermore, gold-labeled antibodies are often used in the rapid test area.

In addition, colloidal gold particles in the high-resolution and ultra-high -resolution test objects for the Rasterelektronenmikroskogie ( SEM), field emission electron microscopy ( FESEM ) and transmission electron microscopy (TEM ) was used.

The optical and electronic properties of colloidal gold promise great advances in microelectronics and microsensors.