Drug Test Result "Positive"
Figure 5 shows a schematic diagram of a test strip used for the detection of morphine. After sampling, the collected sample is expressed into the SPC and delivered into the cassette, which contains a lateral-flow strip of nitrocellulose impregnated with test and reference lines. In the lateral-flow strip, phosphor-antibody complexes mix with sample/buffer and move by capillary action along the test strip. If the sample does not contain any morphine, the antibodies cross the membrane and bind with the membrane-fixed morphine molecules in the test zone (Fig. 5, top). When morphine is present in the oral-fluid sample, the drug will complex with the phosphor-antibody conjugate during flow. Upon reaching of the test lines, there is no reaction of the phosphor-antibody conjugate with the membrane-fixed morphine molecules in the test zone, because the active sites on the antibody are already occupied by the drug in the sample. Consequently, the subsequent analysis of the test lines using the Drager Drug-Test Analyzer will not produce a signal (Fig. 5, bottom). The assay reference band will not be influenced by the presence or absence of drug in the oral fluid and, therefore, will be present in all reactions.
On a multi-analytical test strip, different substances can be detected simultaneously. Figure 6 (left side) shows a schematic diagram of a test strip with three distinct and physically separate test zones to detect, e.g., cannabis, cocaine, and amphetamines. As a result of the immunological detection reaction, the antibodies coupled to the UPT particles will bind exclusively in the test zone corresponding to their drug (cocaine, cannabis, amphetamine). Through the changing of their composition, phosphor particles of varying emission spectra can be produced, allowing multiplexed testing. The use of different phosphors allows differentiation of different binding reactions without necessitating the physical separation of the test zones on the test strip. In the example shown in Fig. 6 (right side), amphetamine-specific antibodies are solely coupled to phosphors that emit green light, whereas cannabis-specific antibodies are fixed to phosphors that emit blue light. By means of clear spectral separation of the two emission spectra using optical filters in the Drager DrugTest Analyzer, it is then possible to detect separately green and blue light at the same spot and, therefore, the different drugs—in this case amphetamine and cannabis—associated with them. Unlike other labeling technologies (e.g., gold particles), the use of UPT can increase not only the sensitivity, but also the selectivity of the analysis.
Fig. 6. (opposite page) Schematic diagram of a test strip with three distinct and physically separate test zones to detect, e.g., cannabis, cocaine, and amphetamines (multi-analytical test strip, left side), and a schematic diagram of a test strip with one test zone, allowing multiplexed testing to detect, e.g., cannabis and amphetamines (right side).
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