Gold, colloidal metallic nature

The choice of polymer is determined by considering the solubility of the metal colloid precursor, the solvent of choice, and the ability of the polymer to stabilize the reduced metal particles in the colloidal state. Natural polymers such as gelatin and agar were often used before the advent of synthetic polymer chemistry, and related stabilizers such as cellulose acetate, cellulose nitrate [23] and cyclo-dextrins [24] have been used more recently. Thiele [25] proposed the Protective Value as a measure of the ability of a polymer to stabilize colloidal metal. It was defined, similar to the older Gold Number of Zsigmondy, as the weight of the... 

Well-defined sites either found in the natural protein or inserted via genetic engineering are decorated with metal particles deposited from the aqueous or gas phase. Dieluweit et al. constructed a super-lattice of uniform gold colloids with a precise repetitive distance of 13 nm based on the Slayer grid of Bacillus sphaericus using chemical modification with thiol-groups as artificial anchorpoints. 

As was mentioned in the previous section, the nature of the substrate is extremely critical in obtaining the maximum enhancement. For visible Raman excitation, the noble metals, such as Ag and Au, and the alkali metals are the substrates of choice. For other regions, other substrates are more suitable (e.g., Ge or Pt in the IR region). Probably the most common substrates used for SERS are the colloidal suspensions of silver or gold particles ( 5-20nm in diameter), and electrochemically roughened silver electrodes. 

Several metals have been used to catalyze redox reactions the most commonly studied are platinum and gold. There is debate concerning the exact catalytic nature - homogeneous or heterogeneous - of these catalysts. We summarize the results on the dependence of the reaction rate and TOP for redox reactions catalyzed by colloidal nanoparticles on (1) particle size, (2) local particle environment, (3) particle concentration, and (4) particle shape. 

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