Conductimetric membrane strip immunosensor with polyaniline-bound gold colloids as signal generator

For point-of-care examination, an immuno-chromatographic assay system based on conductimetric detection was investigated by utilizing, as signal gener ator, colloidal gold with polyaniline bound on the metal surface. Although the gold is a widely used label for antibodies to produce colorimetric sign als, the tracer does not lend itself for a suitable electric conduction alo ng the gold particles due to the presence of protein barriers (e.g, immunog lobulin and blocking agent) against electron transfer. To overcome this pro blem, we introduced a conducting polymer, for instance, polyaniline, as a c onductivity-modulating agent on the gold surface after immobilizing an anti body specific to human albumin used as model analyte, This novel signal gen erator amplified the conductimetric signal 4.7 times compared with the plai n gold, and the signal was also maximum 2.3-fold higher than that from the photometric system under the same analytical conditions. The latter effect resulted from an exponential pattern in the dose-response curve of the elec tric signal that was different from the conventional sigmoidal shape. (C) 2 000 Elsevier Science S.A. AU rights reserved.