A new method for immunoassays using field-flow fractionation with on-line, continuous chemiluminescence detection.

Chemiluminescence detection has already been combined with different separation techniques such as HPLC and capillary electrophoresis. In this work, it was applied to gravitational field-flow fractionation, a low-cost, flow-assisted separation technique for micronsized particles suited to further on-line detection of the separated analytes. Horseradish peroxidase was used as model sample, either free in solution or immobilized onto micronsized, polystyrene beads. The chemiluminescent substrates were added directly into the mobile phase, and the continuous, steady-state chemiluminescence generated during elution was detected on-line by either a flow-through luminometer or a CCD camera. Ultra-low detection limits, two orders of magnitude lower than those achievable with spectrophotometric detection, were found. The possibility to fully separate and quantitate free and bead-immobilized enzymes is reported, as a step towards the development of multianalyte, ultra-sensitive, micronsized beads-based flow-assisted immunoassays.