LFIA kits are testing tools that utilize antigen-antibody reactions to enable low-cost, high-efficiency health diagnostics and crime scene analysis, rapidly detecting target components by direct and competitive methods.
Test kits are widely used to diagnose health conditions or investigate bloodstains at crime scenes. A variety of scientific principles are applied to the creation of these kits, and the need is to make them easy, fast, and accurate at low cost. This need has led to the development of various types of kits that apply antigen-antibody reactions to analyze the components present in a sample.
An antigen-antibody reaction is an immune response in which an antigen is combined with an antibody that reacts specifically to that antigen. Advances in antibody manufacturing technology have led to the development of various types of kits using lateral flow immunoassay (LFIA) that are highly portable and require short analysis times. In particular, these kits are becoming increasingly popular because they can be easily used at home as well as in the medical field. For example, pregnancy test kits or diagnostic kits for certain infectious diseases are based on LFIA technology and are designed to be easily used at home. This is an important innovation that provides convenience to the user while efficiently utilizing medical resources.
LFIA kits make it easy to determine the presence or absence of a target component in a liquid sample by looking at the line that appears on the kit. The LFIA kit is shaped like a long flat rod with a sample pad, a binding pad, a reaction membrane, and an absorption pad arranged side by side in this order. The sample absorbed by the sample pad moves with the complex from the binding pad across the reaction membrane to the absorption pad, where excess sample is absorbed. The complex on the binding pad consists of a specific substance attached to a labeled material, such as gold-nanoparticles or fluorescent beads. The labeled substance is colored by a chromogenic reaction, and the specific substance attached to the labeled substance varies depending on the kit.
In general, kits that detect a single target component have two strands of antibodies immobilized on the reaction membrane in a band, with the strand closer to the sample pad being the test line and the other strand being the standard line. When a labeled substance is placed on either the test or standard, a color reaction causes a reaction line to appear. If the test line is colored, the presence or absence of the target component can be determined. If the standard shows a colored reaction line, the test is successful. These structural characteristics of LFIA kits allow for rapid and accurate testing in a variety of environments.
LFIA kits are primarily manufactured using either the direct or competitive method, which has different implications for the color development of the test line. In the direct method, the specific substance in the complex is an antibody that can bind to the target component. If the sample contains the target component, the target component binds first to this antibody and then to the immobilized antibody on the test line. If the test line is colored, the target component is detected in the sample. In the competitive method, the specific substance in the complex is not an antibody against the target component, but the target component itself. If the sample contains the target component, the target component in the sample and the target component in the complex compete with each other to bind to the test antibody. If there is enough of the target in the sample, the target in the sample will prevent the target in the complex from binding to the antibody in the test, resulting in no color development. The direct method is used to detect bacteria or proteins with large molecular weights, while the competitive method is used when the target component is small, such as antibiotics.
In addition to portability and rapidity, the accuracy of a test kit is also important. To measure the accuracy of a kit, multiple tests are performed using the kit and the results are analyzed. If the kit determines that a sample contains the target ingredient, it is said to be positive. This is a true positive if the target component is actually present in the sample, and a false positive if the target component is not present in the sample. Conversely, if the kit determines that the sample does not contain the target component, it is a negative result. This is called a true negative if the target component is not actually present, and a false negative if the target component is present. In the real world, no kit can eliminate false positives or false negatives.
The accuracy of a kit is calculated from the results of multiple tests, which is the probability of getting the correct result when analyzing a sample. Accuracy is divided into sensitivity and specificity. Sensitivity is the percentage of times a kit tests positive for the presence of a target component in a sample. Specificity is the percentage of times the kit tests positive for the target component when it is not present in the sample. Ideally, a kit with both high sensitivity and specificity would be the most accurate, but in practice this is often not the case, so you should choose a kit based on sensitivity or specificity depending on the situation.
In conclusion, LFIA kits have many advantages as a rapid, simple, and accurate testing tool. Their applications in medical and non-medical fields are becoming increasingly widespread, and with the advancement of technology, more sophisticated and diverse kits are expected to be developed in the future. These kits will play a major role in improving the quality of life for many people by facilitating health management in everyday life and enabling rapid response in a variety of situations.
