An improved coating for the isolation and quantitation of interferon-γ in spiked plasma using surface plasmon resonance (SPR)

A study was initiated to investigate the use of surface plasmon resonance (SPR) for the detection in plasma of a high p I model protein, recombinant human interferon-γ (IFN-γ). Initially a number of self-assembled monolayers (SAMs) and hydrogel-derivatised SAM-coatings were characterised for the adsorptive and desorptive properties of plasma components. Next a monoclonal anti-IFN-γ antibody, MD-2, was covalently attached to dextran-modified mercaptoundecanoic acid surfaces that performed best. On coatings consisting of carboxyl-modified dextran (CMD) a difference in interaction behaviour was observed when IFN-γ was injected in either buffer or diluted plasma. During the injection of IFN-γ in buffer, an acceleration of the interaction process was observed and the signal continued to increase after the injection plug had passed. Upon injection of diluted plasma spiked with IFN-γ, the response increased without acceleration of the binding process. After the injection was finished, some of the bound material desorbed as expected, resulting in a signal decrease. On non-charged dextrans, the interaction between the antibody-modified surface and IFN-γ in either plasma or buffer was similar. During sample injection the response increased with a binding rate depending on the concentration of IFN-γ present in solution. When the injection was finished, some of the bound material was washed away from the surface and only a minor contribution of non-specific adsorbed plasma components was noticeable. From the coatings tested, the non-modified dextran-coated SPR sensor disks prove to be best suited for the detection of IFN-γ in complex matrices like plasma. The interaction of IFN-γ in both diluted plasma and buffer is comparable and concentrations of IFN-γ of 250 ng ml −1 and higher can be detected in both buffer and 100×-diluted plasma. The non-specific adsorption of plasma components is low, whereas the specific IFN-γ response is relatively high.