Escherichia coli with autodisplayed Z-domain of protein A for signal amplification of SPR biosensor.
ABSTRACT Generally, an immunoaffinity SPR biosensor detects a target analyte in a sample through highly selective adsorption by using the antigen-antibody interaction. For improving the sensitivity, various kinds of particles have been added to the already bound analytes on the SPR biosensor (sandwich assay). In this work, signal amplification was demonstrated by the expression of the IgG-binding Z-domain of protein A on the outer membrane of Escherichia coli via "Autodisplay". The amount of Z-domain of protein A expressed on the outer membrane was calculated to be 280,000 molecules per cell. In addition, the IgG-binding ability of the expressed protein was characterized using FACS analysis. The signal amplification of the SPR biosensor was performed in the sandwich assay format using a model of horseradish peroxidase (HRP); the limit of detection was determined to be significantly improved from 1 microg/ml to 1 ng/ml. Finally, myoglobin analysis was demonstrated for the medical diagnosis of cardiac diseases. The detection limit was estimated to be improved from 10 ng/ml to <1 ng/ml. These results show that Z-domain-displaying E. coli can be successfully used for the signal amplification of immunoaffinity biosensors, thereby improving the sensitivity and the limit of detection.
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ABSTRACT: We have optimized the display of the B domain of staphylococcal protein A on the surface of Lactococcus lactis. The maximum binding capacity was estimated at 0.146 μg of antibody per 10⁸ cells and was sustained at 86% after treatment with simulated gastric juice. A tumor necrosis factor alpha (TNF-α)-binding affibody was also displayed and bound TNF-α, which could be useful in the treatment of inflammatory bowel disease.Applied and environmental microbiology 10/2010; 76(20):6928-32. · 3.69 Impact Factor
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ABSTRACT: Enzyme-linked immunosorbent assay (ELISA) is a common tool to test human sera on an antibody reaction against a specific antigen. The 60-kDa Ro/SS-A antigen for autoantibodies can be found in sera from systemic lupus erythematosus (SLE) patients. As in the case of 60-kDa Ro/SS-A, antigens used in ELISAs are recombinantly expressed in Escherichia coli and time-consuming purification steps are needed to get the proteins. To avoid these disadvantages, 60-kDa Ro/SS-A was expressed on the surface of E. coli using autodisplay, an efficient surface display system. Cells displaying 60-kDa Ro/SS-A on the surface were applied as an antigen source instead of the purified antigen. In total, 39 patients and 30 control sera were screened on a 60-kDa Ro/SS-A antibody reaction. To eliminate antibodies against native E. coli, human sera were preabsorbed with E. coli cells prior to the assay. The new ELISA protocol (surface display ELISA [SD-ELISA]) using E. coli with autodisplayed 60-kDa Ro/SS-A showed a sensitivity of 86.67% and a specificity of 83.33% by a cutoff value of 0.28. Our results show that autodisplay provides simple, rapid, and cheap access to human antigens for an ELISA to screen human sera against specific antibody reactions.Analytical Biochemistry 12/2010; 407(1):72-8. · 2.58 Impact Factor
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ABSTRACT: The surface plasmon resonance (SPR) biosensors have been used to detect various target analytes by using highly specific antigen–antibody interactions. In this work, a parylene film modified to have primary amine groups was applied as a linker layer of the SPR biosensor, and the primary amine groups were used for the covalent immobilization of proteins to the SPR biosensor. The feasibility of the parylene film as a linker layer was presented by estimating the influence of the parylene film on the SPR measurement parameters, such as the sensitivity and the detection range. Then, a model protein called horseradish peroxidase (HRP) was used to demonstrate the improved immobilization efficiency as well as the sensitivity of the SPR biosensor with the parylene-A film. Additionally, a reconstruction method of the immunoaffinity layer was presented by using oxygen plasma.Sensors and Actuators B-chemical - SENSOR ACTUATOR B-CHEM. 01/2011; 154(2):89-95.