Description of test setup
The core of every lateral flow immunoassay are porous nitrocellulose membranes, on which antibodies are usually applied in a line. These membranes enable the sample to migrate through the porous structures, the analyte from the sample being specifically enriched on the fixed antibodies on the membrane.
In addition to the nitrocellulose membrane, other differently functional, successively overlapping membranes are fixed on a self-adhesive plastic card. Before the sample migrates through the nitrocellulose membrane, it is applied to a sample pad, which ensures even distribution and pretreatment of the sample. The sample is transported from the sample pad to the adjoining conjugate pad, into which color-particle-labeled antibodies are introduced. These color particle conjugates bind specifically to the analyte in the sample and are required for visualization on the test line. From there, the sample-color particle-conjugate complex is led into the nitrocellulose membrane, on which a colored line is generated by the analyte enrichment and thus the enrichment of the colored nanoparticles. Excess dye-particle conjugates are bound to a second line on the nitrocellulose membrane and form a second reaction-independent control that indicates the functionality of the test. Finally, the sample is passed on to the wicking pad located behind the control zone and picked up there to prevent backflow.
Characteristics
The lateral flow assay has a number of unique selling points that make it a special POCT. The basis for producing a detection method based on paper strips makes it the most cost-effective immunoassay worldwide. The use of antibodies is responsible for sensitive and specific detection. The basis, the migration of liquids through porous structures, make all automation steps and devices superfluous. Added to this is the possibility of scalable production and the greatest advantage, the robustness. Few immunoassays show the same resistance to different environmental conditions as the lateral flow assay.
Some of the often described limitations of LFAs are a thing of the past. Inexpensive and high-quality analysis devices conquer the market and allow quantitative analysis results, where previously only yes / no statements were possible. Novel technologies also enable the establishment of multiplex analyzes.
Outlook
The translation of various research results to other POCT approaches, such as lab-on-a-chip technology, is difficult for a variety of reasons. The well-established LFA technology, on the other hand, is very well equipped for future challenges and applications.