Biomaterial Database

Noncompetitive immunoassays using bifunctional unilamellar vesicles or liposomes. 1995

A K Singh, and P K Kilpatrick, and R G Carbonell

Department of Chemical Engineering, North Carolina State University, Raleigh 27695-7904, USA.

Small unilamellar vesicles (SUVs) functionalized with an enzyme label and with specific ligands for biological molecules are useful as signal enhancement vehicles in the development of enzyme-linked immunoadsorbent assays and other biosensor applications. Bifunctional vesicles were prepared by covalently attaching horseradish peroxidase (HRP) and an antibody to the outside of the lipid bilayer of an SUV. The reaction conditions were optimized to obtain 7-12 antibody molecules and 100-200 HRP molecules per vesicle. The enzyme retained 70-80% of its specific activity after immobilization, and the presence of immobilized proteins on the vesicle surface apparently increased the vesicle stability. To minimize the background signal and maximize the specific signal, the immunoassay protocol was optimized with respect to (1) the type and concentration of blocking agent, (2) the diluents for HRP-antibody-vesicles and sample, (3) the incubation period, and (4) the incubation temperature. The bifunctional vesicles were used in a noncompetitive immunoassay to detect d-dimer, a fibrin dimer formed at the early stages of thrombosis. A second conjugate, HRP-antibody, was prepared, characterized, and used as a control against which to compare the assay using vesicles. The assay results using vesicles led to a detection limit for d-dimer in human plasma 9 times lower than what was achieved using the conventional enzyme-antibody conjugate assay.

UI	MeSH Term	Description	Entries
D007118	Immunoassay	A technique using antibodies for identifying or quantifying a substance. Usually the substance being studied serves as antigen both in antibody production and in measurement of antibody by the test substance.	Immunochromatographic Assay,Assay, Immunochromatographic,Assays, Immunochromatographic,Immunoassays,Immunochromatographic Assays
D008024	Ligands	A molecule that binds to another molecule, used especially to refer to a small molecule that binds specifically to a larger molecule, e.g., an antigen binding to an antibody, a hormone or neurotransmitter binding to a receptor, or a substrate or allosteric effector binding to an enzyme. Ligands are also molecules that donate or accept a pair of electrons to form a coordinate covalent bond with the central metal atom of a coordination complex. (From Dorland, 27th ed)	Ligand
D008051	Lipid Bilayers	Layers of lipid molecules which are two molecules thick. Bilayer systems are frequently studied as models of biological membranes.	Bilayers, Lipid,Bilayer, Lipid,Lipid Bilayer
D008081	Liposomes	Artificial, single or multilaminar vesicles (made from lecithins or other lipids) that are used for the delivery of a variety of biological molecules or molecular complexes to cells, for example, drug delivery and gene transfer. They are also used to study membranes and membrane proteins.	Niosomes,Transferosomes,Ultradeformable Liposomes,Liposomes, Ultra-deformable,Liposome,Liposome, Ultra-deformable,Liposome, Ultradeformable,Liposomes, Ultra deformable,Liposomes, Ultradeformable,Niosome,Transferosome,Ultra-deformable Liposome,Ultra-deformable Liposomes,Ultradeformable Liposome
D004797	Enzyme-Linked Immunosorbent Assay	An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed.	ELISA,Assay, Enzyme-Linked Immunosorbent,Assays, Enzyme-Linked Immunosorbent,Enzyme Linked Immunosorbent Assay,Enzyme-Linked Immunosorbent Assays,Immunosorbent Assay, Enzyme-Linked,Immunosorbent Assays, Enzyme-Linked
D006735	Horseradish Peroxidase	An enzyme isolated from horseradish which is able to act as an antigen. It is frequently used as a histochemical tracer for light and electron microscopy. Its antigenicity has permitted its use as a combined antigen and marker in experimental immunology.	Alpha-Peroxidase,Ferrihorseradish Peroxidase,Horseradish Peroxidase II,Horseradish Peroxidase III,Alpha Peroxidase,II, Horseradish Peroxidase,III, Horseradish Peroxidase,Peroxidase II, Horseradish,Peroxidase III, Horseradish,Peroxidase, Ferrihorseradish,Peroxidase, Horseradish
D000906	Antibodies	Immunoglobulin molecules having a specific amino acid sequence by virtue of which they interact only with the ANTIGEN (or a very similar shape) that induced their synthesis in cells of the lymphoid series (especially PLASMA CELLS).
D001667	Binding, Competitive	The interaction of two or more substrates or ligands with the same binding site. The displacement of one by the other is used in quantitative and selective affinity measurements.	Competitive Binding
D013696	Temperature	The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.	Temperatures
D015374	Biosensing Techniques	Any of a variety of procedures which use biomolecular probes to measure the presence or concentration of biological molecules, biological structures, microorganisms, etc., by translating a biochemical interaction at the probe surface into a quantifiable physical signal.	Bioprobes,Biosensors,Electrodes, Enzyme,Biosensing Technics,Bioprobe,Biosensing Technic,Biosensing Technique,Biosensor,Electrode, Enzyme,Enzyme Electrode,Enzyme Electrodes,Technic, Biosensing,Technics, Biosensing,Technique, Biosensing,Techniques, Biosensing