Capillary-based displacement flow immunosensor

We report on the preparation of a novel capillary flow immunosensor for 2,4,6-trinitrotoluene (TNT). Anti-TNT antibody is immobilized onto the silanized inner walls of an 800-mu m-i.d. glass capillary using a heterobifunctional crosslinker, followed by saturating the capillary with fluorophore-labeled antigen. To perform the assay, an aliquot of TNT solution is injected into the capillary. TNT competes for the binding pocket of the fluorophore-labeled antigen, which is detected downstream, We have demonstrated that the sensitivity of the capillary immunosensor is improved by at least 2 orders of magnitude compared to that of conventional packed-column;or membrane-based displacement flow immunosensors. The limit of detection (S/N > 3) for TNT using the capillary immunosensor is 15 pg/mL (7 fmol), and the linear dynamic range is 1-250 ng/mL. The entire assay can be performed in less than 3 min. During 15 injections of 100 ng/mL TNT solution, the signal reproducibility (RSD) was maintained to within 4%.