Preparation of Strept avidin-Gold Complexes

The following protocol is based on the method of Morris and Saelinger (1984) for the labeling of succinylated avidin with gold particles of 5.2nm diameter. Succinylated avidin was used to reduce the pi of the protein, thus eliminating nonspecific binding due to the strong positive 

Prepare a 200 ml gold sol by using white phosphorus reduction as described in Section 2, this chapter. 

Prepare 5 ml of a lmg/ml succinylated avidin solution by dissolving the protein in 50mM sodium phosphate, pH 7.5. 

With stirring, add the succinylated avidin solution to the colloidal gold suspension at room temperature. 

Remove excess protein by centrifugation at a minimum of 50,000g for several hours. 

---