Site-directed immobilisation of antibody fragments for detection of C-reactive protein.

C-reactive protein, CRP antibody Fab'-fragments have been attached on pre-cleaned gold slides and protein repellent polymers have been used to block the remaining free space in between the antibody fragments. At optimal conditions the antibody fragments are site-directly immobilised on the surface and non-specific binding is reduced. The amount of Fab'-fragments in the polymer host monolayer has been optimised for various buffers. Binding of CRP to Fab'-fragment/polymer layers produced in phosphate buffered saline decreased with NaCl salt concentration. In a 1M NaCl phosphate buffer, the antibodies seem to be randomly oriented on the surface with a similar response to CRP as that of an antibody F(ab)(2)-fragment layer. In a 150 mM NaCl phosphate buffer, on the other hand, the fragments seem to be site-directly oriented and the response to CRP was fivefold. The highest response to CRP was obtained to a layer with a Fab'-fragment concentration of 60 microg/ml. CRP could be detected in a concentration range of 1 ng/ml to 50 microg/ml from a standard solution in phosphate buffer and in a range of 4 ng/ml to 50 microg/ml from serum/PBS. CRP was, moreover, successfully detected in patient samples with good reproducibility. The layer would thus be sensitive enough to analyse the CRP concentration in human serum for predicting cardiovascular disease.