Gold, colloidal adsorption

The adsorption of protein on colloidal gold occurs in a relative small pH range. Immunoglobulins are bound at pH 7.4, Protein A has an optimum at pH 6.5. For adjusting the pH, the gold colloid as well as the protein solution are dialyzed twice at RT against a 100-fold volume of Soln. A for 1 h each. 

Pergolese B, Muniz-Miranda M, Bigotto A (2005) Surface enhanced Raman scattering investigation of the halide anion effect on the adsorption of 1,2,3-triazole on silver and gold colloidal nanoparticles. J Phys Chem B 109 9665-9671... 

The double-layer forces between a metal and an insulator as well as between two metal surfaces have also been studied. For example, Biggs and coworkers [127,128] have measured forces between a gold colloidal sphere and a flat gold substrate as a function of ionic concentration and pH. Several groups have carried out measurements of the double-layer forces with molecular adsorptions taking place on the metal surface [129-133]. 

Bedford, E.E., Boujday, S., Humblot, V., Gu, F.X., Pradier, C.-M., 2014. Effect of SAM chain length and binding functions on protein adsorption P-lactoglobulin and apo-transferrin on gold. Colloids Surf. B Biointerfaces 116, 489—496. 

Fig. 2 Laser scanning microscope pictures recorded in reflection from the diazosulfonate terpolymerfilm after UV irradiation through a TEM grid mask and subsequent adsorption of gold nanocolloids brighter areas indicate the gold colloid layer.

A detailed study by Grieser and co-workers [169] of the forces between a gold-coated colloidal silica sphere and a gold surface reveals the preferential adsorption of citrate ions over chloride to alter the electrostatic interaction. 

Separation of colloids by GPC is an important technical advance that may help in the characterization of novel materials. One such separation was the shape separation of gold particles of nanometer size by GPC on a Nucleogel GFC 1000-8 column using sodium dodecyl sulfate and Brij-35 [polyoxyethylene (23) dodecanol] to modulate the adsorption properties of the colloidal gold.42 Rodlike and spherical particles were separated using UV-VIS detection. 

Non-Aqueous Colloidal Metal Solutions. It has been difficult to prepare colloidal gold in non-aqueous media due to limitations in preparative methods (low salt solubilities, solvent reactivity, etc.), and the fact that the low dielectric constant of organic solvents has hindered stabilization of the particles. In aqueous solution the gold particles are stabilized by adsorption of innocent ions, such as chloride, and thus stabilized toward flocculation by the formation of a charged double layer, which is dependent on a solvent of high dielectric constant. Thus, it seemed that such electronic stabilization would be poor in organic media. 

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. 

Geoghegan, W.D. (1988) The effect of three variables on adsorption of rabbit IgG to colloidal gold. J. Histochem. Cytochem. >6, 401-407. 

Nechaev, E. A., Nikolenko, N. V. (1986). Adsorption of chloride complexes of gold(III) on iron-oxides. Colloid Journal of the USSR, 48(6), 992-996. 

---