A method of cross-linking a peptide to form a homopolymer of the peptide, to immobilize the peptide on a solid phase and to enhance antigenicity of the peptide is disclosed. The method comprises the steps of preparing a fusion peptide by incorporating a cross-linking segment including a tetrapeptide sequence Q-X-K-(S/T) (SEQ ID NO: 15) into the peptide and cross-linking the peptide by a glutaminase.