Antigen colloidal gold labeling

One particularly novel carrier was reported to consist of 50-70 nm colloidal gold particles of the type often used in cytochemical labeling techniques for microscopy (Pow and Crook, 1993) (Chapter 24). Adsorption of peptide antigens onto gold and subsequent injection of the complex into rabbits in an adjuvant mixture resulted in rapid production of antibody of extremely high titer. The resultant antibodies could be used in immunocytochemistry at dilutions from l-in-250,000 down to l-in-1,000,000, which is orders-of-magnitude beyond the dilutions typically used with lower-titer antibodies. 

Romano EL, Romano M. Staphyloccal protein A bound to colloidal gold a useful reagent to label antigen-antibody sites for electron microscopy. Immunochemistry 1977 14 711-715. 

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. 

It has been reported that some commercial preparations of colloidal gold-antibody complexes may contain free active antibody. Such free antibody will compete with antibody-colloidal gold particles for antigen binding sites and may reduce labeling intensity. The presence of free protein may be identified using a simple test procedure (20)... 

The up-to-date trends in using colloidal-gold markers for bioanalytical studies are as follows (i) to minimize the analyte substance amount (antigens, oligonucleotides, lectins, etc.) and (ii) to enhance the sensitivity of analysis. For instance, a sensitivity up to 60-70 ng L" has been reported [104] for an assay based on a simple replacing of the nitrocellulose membranes by microarrays combined with a photometrical reader. 11 should be emphasized that the microarray assay utilizes microliter volumes both for analyte probes and for labeled markers. Besides, the photometrical reader, together with the accessory equipment, allows for 384 probes to be analyzed within a short time period. 

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