Biomedical subjects

U Narang

Publications and source records attributed to U Narang.

3 recordsLinked to original sources

PubMed1998

Multianalyte detection using a capillary-based flow immunosensor.

A highly sensitive, dual-analyte detection system using capillary-based immunosensors has been designed for explosive detection. This model system consists of two capillaries, one coated with antibodies specific for 2,4,6-trinitrotoluene (TNT) and the other specific for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) combined into a single device. The fused silica capillaries are prepared by coating anti-TNT and anti-RDX antibodies onto the silanized inner walls using a hetero-bifunctional crosslinker. After immobilization, the antibodies are saturated with a suitable fluorophorelabeled antigen. A "T" connector is used to continuously flow the buffer solution through the individual capillaries. To perform the assay, an aliquot of TNT or RDX or a mixture of the two analytes is injected into the continuous flow stream. In each capillary, the target analyte displaces the fluorophore-labeled antigen from the binding pocket of the antibody. The labeled antigen displaced from either capillary is detected downstream using two portable spectrofluorometers. The limits of detection for TNT and RDX in the multi-analyte formate are 44 fmol (100 microliters of 0.1 ng/ml TNT solution) and 224 fmol (100 microliters of 0.5 ng/ml RDX solution), respectively. The entire assay for both analytes can be performed in less than 3 min.

Antibodies↗

PubMed1997

Fiber optic-based biosensor for ricin.

We report on an evanescent wave fiber-optic biosensor for detecting a potently toxic protein, ricin, in the picograms per milliliter range. A sandwich immunoassay scheme was used to detect ricin. First, an anti-ricin IgG was immobilized onto the surface of an optical fiber in two different ways. In the first method, the antibody was directly coated to the silanized fiber using a crosslinker. Second, avidin-coated fibers were incubated with biotinylated anti-ricin IgG to immobilize the antibody using an avidin-biotin bridge. The assay using the avidin-biotin linked antibody demonstrated higher sensitivity and wider linear dynamic range than the assay using antibody directly conjugated to the surface. The linear dynamic range of detection for ricin in buffer using the avidin-biotin chemistry is 100 pg/ml-250 ng/ml. The limits of detection for ricin in buffer solution and river water are 100 pg/ml and 1 ng/ml, respectively. At higher concentrations of ricin (> 50 ng/ml), we observe a strong interaction of ricin with the avidin coated on the surface of the fibers. We have demonstrated that this interaction is primarily due to the lectin activity of ricin and is significantly reduced using fibers coated with neutravidin or by adding galactose to the ricin samples.

Adsorption↗

PubMed1996

Selective removal of ribonucleases from solution with covalently anchored macromolecular inhibitor.

Poly[2'-O-(2,4-dinitrophenyl)]poly(A)[DNP-poly(A)] has been found to be a potent inhibitor in solution for RNases A, B, S, T1, T2 and H as well as phosphodiesterases I and II. Kinetic measurements with RNase B and RNase T1 showed DNP-poly(A) to be a reversible competitive inhibitor with K1 equal to 1.03 and 1.05 microM, respectively. Data on the quenching of fluorescence of RNase T1 by DNP-poly(A) indicate the existence of more than one RNase-binding site in each DNP-poly(A) molecule. By attaching each DNP-poly(A) molecule at one end covalently to oxirane acrylic beads, an affinity column was prepared for selective removal of RNases from aqueous solutions by simple filtration. It was found that a 1000-fold reduction in RNase concentration can be obtained by passing either 7.0 microM or 7.0 nM RNase A solution through a 5-cm-long column. The column can be saturated by passing through a concentrated RNase solution and subsequently regenerated by washing with salt solution. The regenerated column can be used repeatedly with no significant decrease in RNase-binding affinity and capacity. By titration of the derivatized beads with RNase, the first dissociation constant (Kd) and binding capacity for the bound enzyme can be determined. The (Kd) was found to be 0.66 microM for RNase B and 0.48 microM for RNase T1; the corresponding binding capacities were found to be 21.0 x (10)-8 and 9.6 x (10)-8 mol/g, respectively.

Chromatography, Affinity↗