Capillary waveguide fluoroimmunosensor with improved repeatability and detection sensitivity.

An optical capillary waveguide fluoroimmunosensor based on glass capillaries internally coated with an ultrathin poly(dimethylsiloxane) (PDMS) film is presented. The evaluation of the capillaries developed was done in comparison with aminosilanized [3-(aminopropyl)triethoxysilane, APTES] glass and poly(methylpentene) (PMP) capillaries by immobilizing rabbit gamma-globulins on the internal capillary wall. Following reaction with (R)-phycoerythrin-labelled antibody, the capillary was scanned with a laser beam and the fluorescence waveguided through the capillary wall was detected by a photomultiplier placed at one of its ends. The capillaries developed provided considerably improved protein coating homogeneity (intracapillary coefficients of variation 2.9-6.6%) and repeatability (intercapillary coefficients of variation 2.1-5.0%) compared with APTES-treated ones (7.9-13.4 and 8.5-15.2%, respectively). With use of these capillaries in a sandwich-type immunosensor for the determination of rabbit gamma-globulins, the assay detection limit was improved eightfold (4.4 ng/mL) compared with that obtained using PMP capillaries (35.3 ng/mL), whereas the assay repeatability was improved threefold (intra-assay coefficients of variation 5.9-13.1%) compared with APTES-treated capillaries (15.6-36%).