Colloidal gold
When colloidal gold is called sols ( colloids ), or gels of tiny gold particles with a diameter of 2 to 100 nm . Colloidal gold is characterized by its deep red color, which is due to the small gold particle size.
Manufacturing
By reduction of chloroauric acid [AuCl H 4 ] in boiling aqueous solution with citric acid or in ethereal solution with white phosphor is obtained unstable gold colloids which readily coagulate . That is why stabilizers are added to them, for example citrates and / or detergents such as Tween 20 . Gold colloids can be precipitated from stabilized brines by adding ethanol .
Physical Properties
The plasmon oscillation can be observed in gold colloids : the collective oscillation of the gold electrons against the gold atomic cores . The wavelength of the light absorbed depends on the particle size and particle density: the larger and closer together the particles, the greater the absorbed wavelength. The density is crucial here, as it can lead to induced dipole interaction between the gold particles. Therefore, gold colloids are much more colorful than a compact gold bar.
use
Gold colloids are used to color glasses red; aggregated gold colloids gild porcelain and glasses.
In biochemistry, colloidal gold is used to mark proteins, for example for direct staining of Western blots . The advantage of staining is its high sensitivity and easy implementation. The disadvantage is that subsequent immunodetection is not possible and the color can only be removed (made invisible) under very harsh conditions. Furthermore, gold-marked antibodies are often used in rapid tests. In addition, gold-labeled antibodies can be used as immunogold staining in electron microscopy , e.g. B. for scanning electron microscopy (SEM), field emission electron microscopy (FESEM) and transmission electron microscopy (TEM). Antibody-marked areas of the sample are visible through the electron-dense gold particles. Colloidal gold is used as a carrier material for the gene gun .
The optical and electronic properties of colloidal gold promise great advances in microelectronics and microsensors .
See also
Individual evidence
- ↑ a b Marc Moeremans, Guy Daneels, Jan De Mey: Sensitive colloidal metal (gold or silver) staining of protein blots on nitrocellulose membranes. In: Analytical Biochemistry 145, No. 2, 1985, pp. 315-321, doi : 10.1016 / 0003-2697 (85) 90368-9 .
- ↑ TJ Nelson: Destaining of Nitrocellulose Blots After Staining with Silver or Colloidal Gold . In: Analytical Biochemistry . tape 214 , no. 1 , 1993, p. 325–328 , doi : 10.1006 / abio.1993.1496 .