This invention discloses using SPR technology to simultaneously and quantitatively measure the concentrations of different tumor markers in a serum sample, which can be used to screen for and determine susceptibility to cancer as well as for the differential diagnosis of metastases from an unknown primary tumor. It also discloses an efficient formula to make a mixed SAM that can greatly enhance the immobilization ability of the metal surface in SPR based techniques, which is good for the immobilization of monoclonal antibodies used for cancer susceptibility assessment and for differential diagnosis of metastases from an unknown primary tumor.