**1. Introduction**

The history of lateral flow immunoassay (LFIA, immunochromatography) began in the- 1980s. The first solved task was to transfer pregnancy tests from a specialized laboratory- directly to the point of sample collection [1]. The test strip developed for this purpose fully- complied with the requirements for nonlaboratory diagnostics, and its basic principles- remain to this day.-

© 2018 The Author(s). Licensee IntechOpen. Distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License (https://creativecommons.org/licenses/by-nc/4.0/), which permits use, distribution and reproduction for non-commercial purposes, provided the original is properly cited.

The overall design of the immunochromatographic test strip is shown in **Figure 1**. It is a composite of several membranes of different structures and porosities, fixed on a support. The bundling of the test strip can vary, so it makes sense to consider its design based on what analytical tasks are being performed on its different sites.-


The next two sections are located on the main **working membrane** of the test strip.-


Membrane components of the test strip are fixed on a **plastic support** and partially overlap with each other for effective fluid movement.-

Depending on the tasks to be performed, additional reagents can be used in the test strip, and some of the membranes can be added, combined, or eliminated. However, at the same time, the general design and principle of conducting analytical interactions during the movement of reagents along membranes is preserved.-

Simplification of the analysis is achieved by refraining from additional processing and incubation enhancing the signal as well as by visual (device-free) evaluation of the results. Because of this, traditional LFIA, meeting the needs of practice in simplicity and speed, is generally considered inferior to alternative immunoassays (such as ELISA) in sensitivity.-

At first, this restriction was not critical. Test systems made it possible to control target compounds in diagnostically demanded concentration ranges, which was enough for their mass application. The implementation of standard LFIA protocols for the detection of new compounds was viewed as an exclusively technological task for manufacturing companies, uninteresting in the scientific sense. In this regard, the number of publications on LFIA in the late 1990s to early 2000s was relatively small. It was believed that the all main methodological problems of LFIA had already been solved.-

**Figure 1.** Components of the immunochromatographic test strip and their functions.-
