phage display principle 

Phage display is a kind of long-lasting laboratory platform for the large-scale study of molecules interaction, such as protein-protein, protein-peptide and protein-DNA interactions, and select molecules with the highest affinity for specific targets. The technology was firstly described by Smith (1985), and then be further expanded by such groups of pioneers, e.g. Greg Winter and John McCafferty (Laboratory of Molecular Biology), Richard Lerner and Carlos Barbas (Scripps Research Institute), and Frank Breitling and Stefan Dübel (German Cancer Research Center).

The phage display technique relies on engineering bacteriophages to display interested molecules (e.g. proteins and peptides) on their surface. To achieve this, the gene encoding the interested molecule is inserted into the gene of phage coat protein, which resulting in the expression of interested molecule fused with the coated protein of bacteriophage particles and a linkage between genotype and phenotype. The phage display library is then built up by assembling millions of genetically modified phages, which can be used for further screening and selection. This platform can contribute to mimic natural molecules within the cellular process and detect their interaction with other molecules.
https://www.creative-biolabs.com/phage-display-platform.html