Surface plasmon resonance immunoassay for cortisol determination with a self-assembling denaturalised bovine serum albumin layer on surface plasmon resonance chip

Abstract

A surface modification method has been developed to fabricate surface plasmon resonance (SPR) chip for small molecule determination. A novel denaturalised bovine serum albumin (dBSA)-SPR-chip was fabricated by a self-assembling method, while a dextran-SPR-chip was prepared by using a traditional method. The surface morphologies of the two chips were investigated by atomic force microscopy technology and their optical properties were characterised by using our home-made SPR analytical instrument. The surface binding capacity of the dBSA-SPR-chip is 2.5 times higher than that of the dextran-SPR-chip. On the basis of the experiments of immune reactions between cortisol antibody and cortisol derivative, the sensitivity of the dBSA-SPR-chip is much higher than that of the dextran-SPR-based SPR-chip. The antibody concentration was optimised at about 10 μg/ml in order to obtain high sensitivity, which was used in the followed inhibition immunoassays. The lowest detection limit for cortisol is 1 ng/ml with a linear range of 5-100 ng/ml by using the dBSA-SPR-chip. These dBSA-SPR-chips can also be applied to detect other small molecules based on the indirect inhibitive immunoassay.