Colloidal gold stability

EXAMPLE 13.4 Change of Stability Ratio with Ionic Concentration. Colloidal gold stabilized by citrate ions and having a mean particle radius of 103 A was coagulated by the addition of NaCI04. The kinetics of coagulation were studied colorimetrically and the stability ratio W for different NaCI04 concentrations was determined (Enustun and Turkevich 1963) ... 

Unsupported Au nanoclusters (or those contacting an inert support material such as BN) exhibit strong size-dependent reactivity, with optimal oxidation performance typically reached < 5 nm diameter [59], For example, colloidal gold stabilized by polyvinylpyrrolidone (PVP) shows pronounced size effects in the aerobic oxidation of benzylic alcohols in water under ambient conditions [60]. Figure 2.1 illustrates this phenomenon for p-hydroxybenzyl alcohol oxidation, wherein 1.3 nm Au clusters achieve 80 % conversion, whereas 9.5 nm clusters are catalytically dead. Differential oxygen adsorption onto these gold clusters is believed to play a crucial role in regulating reactivity. 

Monitoring the pH value during the preparation of gold sol, which leads to the below reported results, it has been observed that pH moves from ca. 3.2, before NaBH4 addition, to ca. 6.9, after NaBH4 addition. In this section a discussion of the influence of the initial pH value on the properties of the colloidal dispersion stabilized by a large amount (PVA/Au = 0.67) or a low amount (PVA/ Au = 0.05) of stabilizer is presented. Proper amounts of HCl or NaOH were used to produce the reported pH values. 

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. 

Determine the minimum amount of protein A required to stabilize the colloidal gold sol being used. The colloidal suspension should be adjusted, if needed, with 0.1M K2CO3 to pH 6-7. Measure the pH of the sol using a gel-filled electrode. Determining the stabilization amount of protein A can be done according to the method described in Section 1, this chapter. 

Mix a stabilizing amount of protein A plus an additional 10 percent with the appropriate volume of colloidal gold. For example, Herbener (1989) mixed 10ml of a 14nm gold particle sol at pH 6.9 with 0.3 mg of protein A dissolved in 0.2 ml water. Mix well. 

L. Wu, J. Chen, D. Du, and H. Ju, Electrochemical immunoassay for CA125 based on cellulose acetate stabilized antigen/colloidal gold nanoparticles membrane. Electrochim. Acta 51, 1208-1214 (2006). 

A.L. Crumbliss, J.Z. Stonehuerner, R.W. Henkens, J. Zhao, and J.P. O Daly, A carrageenan hydrogel stabilized colloidal gold multi-enzyme biosensor electrode utilizing immobilized horseradish peroxidase and cholesterol oxidase/cholesterol esterase to detect cholesterol in serum and whole blood. Biosens. Bioelectron. 8, 331-337 (1993). 

Add 10 mL of colloidal gold to 0.2 mL of protein solution containing the minimal amount of protein needed to stabilize the gold plus 10% (as determined in step 3) (see Note 2). 

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... 

The method of laser ablation from a metal has been used to prepare nanoparticles dispersed in a solution [202-207]. Recently, colloidal gold nanoparticles in water having an average diameter of 5.5 nm were prepared by laser ablation at 1064 nm (800 mJ/cm ) from a gold metal plate [208]. The final nanoparticle size depends on the laser fluence and the stabilizer concentration (Fig. 17). 

Mix a stabilizing amount of antibody plus an additional 10% with the appropriate volume of colloidal gold. For example, Geoghegan (1988) found that an addition of 10-14 pg of antibody per milliliter of gold colloid resulted in stable preparations. Mix well after addition of antibody to the gold suspension. 

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