Abstract
Carcinoembryonic antigen (CEA) is an oncofoetal cell-surface glycoprotein that serves as an important tumor marker for colorectal and some other carcinomas. In this work, a CEA immunoassay using a surface plasmon resonance (SPR) biosensor has been developed. SPR could provide label-free, real-time detection with high sensitivity, though its ability to detect CEA in human serum was highly dependent on the analytical conditions employed. We investigated the influences of various analytical conditions including immobilization methods for anti-CEA antibody and composition of sensor surface on the selective and sensitive detection of CEA. The results show that anti-CEA antibody immobilized via Protein A or Protein G caused a large increase in the resonance signal upon injection of human serum due to the interactions with IgGs in serum, while direct covalent immobilization of anti-CEA antibody could substantially reduce it. An optimized protocol based on further kinetic analysis and the use of 2nd and 3rd antibodies for the sandwich assay allowed detecting spiked CEA in human serum as low as 25 ng/mL. Furthermore, a self-assembled monolayer of mixed ethylene-glycol terminated alkanethiols on gold was found to have a comparable ability in detecting CEA as CM5 with thick dextran matrix and C1 with short flat layer on gold.
Highlights
Diagnosis at an early stage and prognosis for successful therapeutic intervention are essential for the recovery of a cancer patient
We used anti-mouse rabbit IgG polyclonal antibody, Protein A and Protein G
Immobilization via Protein A and Protein G should allow most of the Fab portions of the immobilized anti-Carcinoembryonic antigen (CEA) IgG accessible to the antigen (CEA) [18, 19]
Summary
Diagnosis at an early stage and prognosis for successful therapeutic intervention are essential for the recovery of a cancer patient. CEA purified from liver metastases of colon carcinoma and pleural and ascites fluids, and quantitatively detected more than 120 glycans on human CEA [4]. Different glycosylation profiles between CEAs of liver metastases of colon carcinoma and pleural and ascites fluids were observed. In this regard, it will be very important quantify CEA level in serum and quantitatively evaluate glycoforms attached for the improved sensitivity and specificity of diagnosis and prognosis. To the best of our knowledge, the detection of the cancer marker CEA in human serum using a SPR biosensor is reported here for the first time. A sandwich assay was performed by applying second and third antibodies to increase the SPR sensitivity and the possibility to detect antigens of even smaller amount in serum sample
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