Flow sandwich immunoassay for specific anti-OVA IgG antibody by use of surface plasmon resonance sensor

A simple and sensitive method for the determination of a specific IgG antibody against ovalbumin (anti-OVA IgG antibody) for diagnosis of egg allergy by use of a surface plasmon resonance (SPR) immunosensor in a flow system is described. An OVA conjugate was immobilized on a sensor chip via a self-assembled monolayer of 11-mercaptoundecanoic acid through an amino coupling method. The determination of the anti-OVA IgG antibody was based on a kind of sandwich immunoassay using an anti-IgG secondary antibody in order to enhance the sensitivity of the SPR immunosensor. The sensitivity and detection limit of the present method for the anti-OVA IgG antibody were 7 mdeg/ppm and 300 ppb, respectively. The present method showed an enhanced sensitivity and detection limit for the determination of the anti-OVA antibody, compared with a direct immunoassay, by which the sensitivity and detection limit were 3 mdeg/ppm and 1 ppm, respectively. By assuming a Langmuir type of adsorption isotherm, the affinity constants of an anti-OVA IgG antibody immunocomplex with the anti-IgG secondary antibody and of the anti-OVA antibody to the OVA conjugate immobilized on the sensor chip were calculated to be 2.1 × 106 M−1 and 2.0 × 106 M−1, respectively. The present flow immunoassay for the anti-OVA IgG antibody by an SPR sensor has potential applications in both research and diagnosis of egg allergy.