Abstract: A flow-through cell for the real-time capacitance monitoring of immunochemical interactions has been developed. It consists of a tantalum strip onto which tantalum oxide was grown electrochemically to a layer thickness as small as 5 nm. Antibody or antigen was immobilized onto the tantalum oxide surface, and binding of the corresponding analyte resulted in modification of the elec. capacitance of the system. With mouse IgG as the ligand, real-time monitoring of anti-mouse-IgG in the nanogram per mL range was possible. The behavior of the system with respect to analyte size and concentration. was investigated. The tantalum/tantalum oxide/electrolyte system can be manufactured easily and reproducibly.

Abstract: Plasma containing α-(difluoromethyl)ornithine (eflornithine hydrochloride; I) was diluted 200-fold with phosphate buffer, pH 7.4, and incubated with an affinity-purified antibody, conjugated to horse-radish peroxidase, for 15 min at room temperature Portions were injected into a carrier stream (0.3 ml/min) of the same buffer and the excess antibody was separated on a column (6 cm x 3.8 mm) of Reacti-Gel HW-65F beads to which a conjugate of the I with BSA was covalently attached. The outflow from this column, containing the bound I, was mixed with 10 mM 3-(p-hydroxyphenyl)propionic acid and 5 mM H2O2 in phosphate buffer, pH 8.5 (0.3 ml/min) and the fluorescence was measured at 405 nm (excitation at 320 nm). Calibration graphs were rectilinear for 0.05-2.5 nM-I with a detection limit of 20 pM and within-run RSD (n = 6) of 2.6, 0.5, and 2.4% and between-run (n = 5) of 6.3, 2.2 and 4.3% for 0.21, 0.84 and 1.7 nM-I, respectively. Cross-reaction with ornithine and putrescine was eliminated by the purification of the antibody. The Reacti-Gel column was used for 50 samples before regeneration. The method gave good correlation with the results from an amino-acid analyzer., with post-column detection with o-phthalaldehyde (r = 0.94, n = 76). A noncompetitive flow injection immunoassay method has been developed to assay small haptens. In this assay the sample containing the hapten is incubated with excess enzyme-labeled monovalent antibody for a brief period. The excess antibody is then separated from the bound antibody by eluting through an antigen-immobilized immunoaffinity column. The enzyme label of the eluting antibody-hapten complex is fluorometrically detected. The applicability of the method is demonstrated by assaying α-(difluoromethyl)ornithine (DFMO), an anticancer drug in human plasma samples. The assay is sensitive enough to detect 200 amol of DFMO. Interferences from other similar endogenous amines have been eliminated by selective immunoaffinity purification of the antibodies.

Abstract: The cited sensor has active sensing components consisting of a reaction cartridge containing a carrier with the immobilized receptor layer and an ISFET sensor mounted in a flow-through cell. Detection involved using urease as a pH-shifting marker enzyme. Cellulose nitrate membranes (0.45 µm pore size) were mounted in a special flow-by cartridge. Borosilicate capillaries were used as columns (10 cm x 0.8 mm) with the antigen molecules immobilized on the inner surface. The system was able to detect antibodies reactive against different peptide sequences of HIV. Measurements were carried out with use of both highly purified murine monoclonal antibodies and more realistic animal samples. The sensitivity was comparable with that obtained by conventional microtitre-plate ELISA tests. Rapid immunosensing was possible using well-defined monomolecular receptor layers.