Exosomes are cell-derived vesicles that are secreted by both normal and cancer cells. Over the last decade, a few studies have revealed that exosomes cross talk and/or influence major tumor-related pathways such as angiogenesis and metastasis involving many cell types within the tumor microenvironment. The protein composition of the membrane of an exosome reflects that of the membrane of the cell of origin. Because of this, tumor-derived exosomes differ from exosomes that are derived from normal cells. The detection of tumor exosomes and analysis of their molecular composition hold promise for diagnosis and prognosis of cancer. Here, we present hydrogel microarrays (biochips), which contain a panel of immobilized antibodies that recognize tetraspanins (CD9, CD63, CD81) and prognostic markers for colorectal cancer (A33, CD147). These biochips make it possible to analyze the surface proteins of either isolated exosomes or exosomes that are present in the serum samples without isolation. These biochips were successfully used to analyze the surface proteins of exosomes from serum that was collected from a colorectal cancer patient and healthy donor. Biochip-guided immunofluorescent analysis of the exosomes has made it possible for us to detect the A33 antigen and CD147 in the serum sample of the colorectal cancer patient with normal levels of CEA and CA19-9.