Additive assay of cancer marker CA 19-9 by SPR biosensor

The detection of a cancer marker, carbohydrate antigen (CA 19-9) was performed by the additive assay which aims for immunoaffinity biosensors to measure the samples without any chemical treatment between analyses. Each concentration of the continually injected sample was calculated from the actually measured signal by using the correlation curve between the accumulated concentration and the accumulated signal. From the comparison between the real and the calculated concentration of CA 19-9, the error was estimated to be around 5% and the detection limit of CA 19-9 was calculated to be 410.9 U/ml. In order to improve the sensitivity of CA 19-9 detection, the antibodies against CA 19-9 was additionally injected after each sample injection for the formation of sandwich complex, and the detection limit was improved to be 66.7 U/ml.