Protein-Colloidal Gold Conjugates

Protein-labeled colloidal gold probes suit as well as for immuno-histochemistry in electron microscopy as for detection of antigens or glycoproteins on blots. There are several protocols for enhancement of electron density and visible color resulting in higher sensitivity. 

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Ready-to-use blocking solutions containing normal inactivated sera or BSA for use with colloidal gold conjugates are available from Aurion (http //www. aurion.nl/). When labeling with protein A and protein G conjugates, this step can be omitted. 

Colloidal gold A suspension (or colloid) of submicrometer-sized particles of gold in a fluid, usually water. A colloidal gold conjugate consists of gold particles coated with a selected protein or macromolecule, such as an antibody, protein A or protein G. Because of their high electron density, the gold particles are visible in the electron microscope without further treatment. 

Colloidal gold-antibody conjugates are also widely used, especially in indirect immunocytochemical methods. However, the stability of these gold conjugates is less than that for protein A, and depending on the antibody, the affinity may be less. Colloidal gold conjugated to avidin (see... 

Incubate grids for 30 min at room temperature in colloidal gold conjugated with protein A, protein G, immunoglobulin, or if a biotinylated secondary antibody was used, streptavidin (see Note 6). 

IgG conjugated colloidal gold is less stable than Protein A or Protein G gold. A recent study suggests that IgY from chickens may produce a more stable colloidal gold conjugate than IgG (9). 

In another application, an optical trap was used to manipulate cell-surface proteins (29). First, colloidal gold particles conjugated to monoclonal antibod-... 

General Method for Conjugating Proteins to Colloidal Gold... 

Rohnnger, R. and Holden, D W (1985) Protein blotting detection of protein with colloidal gold, and of glycoproteins and lectins with biotin-conjugated and enzyme probes Anal Biochem. 144, 118-127. 

Electrolyte-mediated coagulation forms the basis for creating all gold conjugates with other molecules. If macromolecules such as proteins are present in the colloidal suspension as the electrolyte concentration is raised to surpass the negative repulsion effects, then adsorption will occur with the protein molecules instead of with other... 

Biotin is a small vitamin molecule (Mr 244) that binds with highaffinity (kD 10 I5M I) to avidin. Avidin is a larger glycoprotein molecule (Mr 70,000), mostly distributed in egg whites. This protein has the advantage of conjugating with different markers, including peroxidase, fluorescent dyes, colloidal gold, and ferritin. Because of this property it is... 

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