Since the early 1980s, home-use pregnancy tests have played an important catalytic role in the applications of lateral-flow immunoassays in point-of-collection (POC) drugs-of-abuse (DOAs) testing. Today, the worldwide market demand for DOA testing devices is enormous, and the diverse application of these testing systems continues to increase. Such devices have the advantage of easy application as compared with instrumented devices, and the results are available immediately. A lateral-flow test strip typically consists of four parts: the sample pad, the conjugate pad, the nitrocellulose membrane, and the absorbent wick. The assembly and characteristics of these dry parts are discussed in other chapters (see Chapters 4 and 6). The proper functioning of the device, however, depends on the maintenance of the right conditions of the chemical buffers, the surfactants, and other molecules. Finally, there are also the biological components—the proteins and specific antibodies that allow visualization of the results. This chapter will describe the principles of this detection system and precautions to take in its preparation.

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