Fig. 1

Example of nitazene test strip images obtained from the limit of detection experiments, along with their visually assigned scores by two independent raters and their ImageJ scores. If both raters were confident that a test line was present or absent, the test was scored as negative (‘-’) (a-e) or positive (‘+’) (g), respectively. The test was indeterminate (‘?’) (f) if at least one of the raters had a lack of confidence in assessing the readout. The images depict one representative readout for each tested concentration of isotonitazene from NTS lot A, selected from a total of 6 replicate measurements conducted on three different days, with duplicates run each day (Fig. 2)