Multiple-analyte fluoroimmunoassay using an integrated optical waveguide sensor

A silicon oxynitride integrated optical waveguide was used to evanescently excite fluorescence from a multianalyte sensor surface in a rapid, sandwich immunoassay format. Multiple analyte immunoassay (MAIA) results for two se ts of three different analytes, one employing polyclonal and the other mono clonal capture antibodies, were compared with results for identical analyte s performed in a single-analyte immunoassay (SAIA) format. The MAIA protoco l was applied in both phosphate-buffered saline and simulated serum solutio ns. Point-to-point correlation values between the MAIA and SAIA results var ied widely for the polyclonal antibodies (R-2 = 0.42-0.98) and were accepta ble for the monoclonal antibodies (R-2 = 0.93-0.99). Differences in calcula ted receptor affinities were also evident with polyclonal antibodies, but n ot so with monoclonal antibodies. Polyclonal antibody capture layers tended to demonstrate departure from ideal receptor-ligand binding while monoclon al antibodies generally displayed monovalent binding. A third set of three antibodies, specific for three cardiac proteins routinely used to categoriz e myocardial infarction, were also evaluated with the two assay protocols. MAIA responses, over clinically significant ranges for creatin kinase MB, c ardiac troponin I, and myoglobin agreed well with responses generated with SAIA protocols (R-2 = 0.97-0.99).