As shown below, the peptide array is directly synthesized on a membrane with a maximum capacity of 384 peptide dots. The membrane is then overlaid with a purified target protein, followed by immunoblotting to find the interaction between the target protein and selective peptide dots. The minimum peptide sequence sufficient to bind to the target protein is revealed by analyzing several adjacent dots that all show positive binding with the target protein. Selected peptide candidates will be linked with a membrane-permeable sequence (roughly 10 aa long) so that they can penetrate both the blood-brain barrier and the plasma membrane of cells. We have used this technique extensively to identify small peptide sequences (roughly 10 aa long) that can be applied for either interference of protein-protein interaction by binding to the interaction interface of target proteins or selective knockdown of endogenous proteins using our peptide-mediated protein knockdown technology.