|Any particular antibody fragment can be isolated from the 'library' using the technique of affinity purification, shown in Figure 11. This technique is based on the highly specific binding of an antibody with its antigen. The phage particles can be recovered from the column and cloned to produce many copies of the antibody fragment.
A mixture of phage particles is passed into the top of the antigen affinity column. The column's surface holds antigen molecules specific to the required antibody fragments.
Phages displaying the required antibody fragment bind to the antigen molecules and are held in the column.
Having been separated from the mixture, the desired phage molecules are washed free from the column. They can then be cloned.