Immunosensor systems have been developed for the rapid and sensitive determination of pesticides, using the insecticide carbaryl as a model analyte. The systems are based on the principle of heterogeneous competitive enzyme immunoassay and used mouse monoclonal anti-carbaryl antibodies either in solution (indirect format) or immobilized (direct format). In both formats, enzyme label (horseradish peroxidase, HRP) and fluorometric detection were employed. In the direct format, antibodies were immobilized on a hydrazide-derivatized agarose gel, and 6-[((1-naphthyloxy)carbonyl)amino]hexanoic acid (CNH hapten) conjugated to HRP was used as the enzyme tracer. The limit of detection was 26 ng L-1 (11 min/assay), and the useful life of the sensor was 60−70 cycles. In the indirect format, CNH conjugated to bovine serum albumin was immobilized on an N-hydroxysuccinimide-derivatized agarose gel, and a rabbit anti-mouse antibody labeled with HRP was used as a secondary immunoreagent. The limit of detection was 284 ng...