Thus, in a preferred embodiment of the present invention, a conjugate between TCPN and a protein such as bovine serum albumin (BSA) is prepared by first thiolating the protein with 2-iminothiolane (Traut's reagent) and then adding the TCPN. The resulting conjugate is then used either as an immunogen, to immunize an animal, or as a screening antigen to test an antibody preparation.