Immunoglobulin G Determination in Human Serum and Milk Using an Immunosensor of New Conception Fitted with an Enzyme Probe as Transducer

To completely overcome the problem of the presence of urea in the serum, which can be the cause (especially at low immunoglobulin G concentrations) of a small but non negligible interference in the enzyme reaction of the enzymatic marker, when the measurement was performed by a potentiometric immunosensor that we constructed and characterized in previous work, and which used urease as marker, we have now constructed an entirely different and highly innovative immunosensor. This new device uses the enzyme alkaline phosphatase as marker, sodium phenylphosphate as substrate but above all, a tyrosinase biosensor obtained by coupling a Clark type gas diffusion amperometric electrode and the tyrosinase enzyme, immobilized in a cellulose triacetate membrane, as transducer. After optimizing the 'competitive' measurement procedures, the new immunosensor was used to determine both HIgG and the anti-HIgG, with a limit of detection (LOD) of the order of 3x10-11 M. Clearly this highly innovative construction geometry makes the immunosensor extremely selective. This makes it possible to determine immunoglobulin G both in human serum and milk without the slightest interference by any urea present in these biological matrixes.