Colloidal gold based probes

A report of a particle-based FPIA<56) details improvement in the limit of detection by two orders of magnitude over a conventional FPIA format for rabbit IgG, to 10 ° M. Goat anti-rabbit capture antibody (binder) is immobilized on polystyrene microspheres or colloidal gold particles, and the sample competes with a fluorescein-labeled rabbit IgG probe. The observed increase in sensitivity is apparently due to the large increase in effective mass of the binding complex. The polarization range is rather limited, though, reportedly due to low concentrations of immobilized antibodies. 

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. 

O. J. F. Martin and co-workers [8] for the interacting plasmon resonant nanoparticles. The possible location of a molecular probe is some point between two or more islands on gold surface. We suppose that these points generate so called hot spots [9] on self-aggregated colloids that are exclusively active in SERS. The simple theoretical evaluations based on the field superposition near the dissipative medium are also in good agreement with the distance dependence obtained by us and the model of molecular probe location. 

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