Abstract
Existing methods of detecting explosives have many problems in terms of stability, sensitivity, high selectivity, and rapid sensing for any given situation. In this study, we selected a displacement method using a surface plasmon resonance (SPR) immunosensor, which is one of the ways to overcome these problems. In an SPR displacement immunoassay, the methods to realize a high sensitivity were investigated by experimental findings. However, they were not investigated by theoretical approaches. Hence, we developed a method with a higher sensitivity based on the kinetic theory of this system. The strategy of an SPR displacement immunoassay to realize a high sensitivity was determined using the two-layer model simulation by a theoretical approach. As a result of the simulation, we found that a high sensitivity was realized using a combination of an antigen analogue and an antibody with a small association constant or a combination of an antigen and an antibody with a large association constant. This means that the equilibrium constants affect the sensitivity of an SPR displacement immunoassay, which is one of assays under nonequilibrium conditions. In addition, we investigated the relationship between association equilibrium constants and the sensitivity using conjugates and a hapten to detect 2,4,6-trinitrotoluene (TNT). The result of the experiment supported the theoretical inferences.
Highlights
Various explosive detection methods have been used to prevent damage from explosives
surface plasmon resonance (SPR) immunosensors, which have high stability based on SPR as the sensing principle and high selectivity based on antigen-antibody interaction, can be used for real-time sensing.[1,2] SPR sensors can measure changes in refractive index over a gold film surface in real time and with high sensitivity without labeling using resonance between electrons on the gold film surface and light
In the case of using a low molecular weight antigen, the SPR immunoassay requires opposite composition; i.e., an antigen or an antigen analogue as a ligand immobilized on the sensor surface and an antibody as an analyte to induce antigenantibody interactions.[1,2,4,5,6,7,8,9] As the molecular weights of antibodies are generally about 150,000, they cause a refractive index change sufficiently large to be detected by highly sensitive SPR sensors
Summary
Various explosive detection methods have been used to prevent damage from explosives. In the case of using a low molecular weight antigen, the SPR immunoassay requires opposite composition; i.e., an antigen or an antigen analogue as a ligand immobilized on the sensor surface and an antibody as an analyte to induce antigenantibody interactions.[1,2,4,5,6,7,8,9] As the molecular weights of antibodies are generally about 150,000, they cause a refractive index change sufficiently large to be detected by highly sensitive SPR sensors. In the displacement method using SPR immunosensors, guides for combinations of antigens, antigen analogues, and antibodies, which enable a more sensitive detection of YYYY Y. explosives, were suggested by the experimental results of 10 ppb TNT.[1] no experiment was performed for a wide range of TNT concentrations, and the guides for combinations were not investigated theoretically. The purpose of this study is to theoretically find strategies for combinations of antigens, antigen analogues, and antibodies, which enable a more sensitive detection of explosives (preferably, 100 ppt sample detectable)
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