The development of a four-band capillary optical immunosensor for the simultaneous determination of mesotrione, hexaconazole, paraquat, and diquat is described. Four distinct bands (each corresponding to a different analyte) are created in the internal walls of a plastic capillary by immobilizing protein conjugates of the analytes. To perform the assay, the capillary is filled with a mixture of anti-analyte-specific antibodies together with a standard or sample containing the analyte(s). After a short incubation, a mixture of the appropriate second antibodies labeled with fluorescein is introduced into the capillary. To measure the fluorescence intensity bound onto each band, the capillary was scanned, perpendicularly to its axis, by a laser light beam. Part of the emitted photons were trapped into the capillary walls and waveguided to a photomultiplier placed at the one end of the capillary. The analytical characteristics of the assays of mesotrione, paraquat, diquat, and hexaconazole were as follows: detection limits of 0.04, 0.06, 0.09, and 0.10 ng/mL, respectively; dynamic ranges up to 9, 6, 12, and 15 ng/ mL, respectively, intra- and interassay CVs less than 10%. The analytical characteristics of the assays were comparable with those of the corresponding single-analyte fluoroimmunoassays performed in microtitration wells, proving the ability of the proposed immunosensor for reliable multianalyte determinations. Moreover, the combination of low-cost disposable plastic capillary tubes with the low consumption of reagents, the short assay time, and the multianalyte feature of the proposed immunosensor indicates its potential for environmental analysis.

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The early diagnosis of acute myocardial infarction requires the determination of several markers in serum shortly after its incidence. The markers most widely employed are the isoenzyme MB of creatine kinase (CK-MB) and the cardiac troponin I (cTnI). In the present work, a capillary waveguide fluoroimmunosensor for fast and highly sensitive simultaneous determination of these markers in serum samples is demonstrated. The dual-analyte immunosensor was realized using glass capillaries internally modified with an ultrathin poly(dimethylsiloxane) film by creating discrete bands of analyte-specific antibodies. The capillary was then filled with a mixture of sample and biotinylated detection antibodies followed by reaction with streptavidin-horseradish peroxidase and incubation with a fluorescently labeled tyramide derivative to accumulate fluorescent labels onto immunoreaction bands. Upon scanning the capillary with a laser beam, part of the emitted fluorescence is trapped and waveguided through the capillary wall to a photomultiplier placed on one of its ends. The employment of tyramide signal amplification provided detection limits of 0.2 and 0.5 ng/mL for cTnI and CK-MB, respectively, in a total assay time of 30 min compared to 0.8 and 0.6 ng/mL obtained for the corresponding assays when the conventional fluorescent label R-phycoerythrin was used in a 65-min assay. In addition, the proposed immunosensor provided accurate and repeatable measurements (intra-assay and interassay coefficients of variation lower than 10%), and the values determined in serum samples were in good agreement with those obtained with commercially available enzyme immunoassays. Thus, the proposed capillary waveguide fluoroimmunosensor has all the required characteristics for fast and reliable diagnosis of acute myocardial infarction.