Test line intensities were analysed using ImageJ software using a procedure depicted in the Supplementary Information (Figure ). In summary, test strip images were converted into a greyscale image. A rectangular selection box of 500 pixels in height and 200 pixels in width was drawn to include the test line region of interest. Values relating to intensity per pixel -such that pixels were averaged (mean) across the width of the strips -were then generated and plotted. In mitigating against potential bias when determining the test line signal, test line intensity was assigned based on the maximum value within the region of interest. To avoid bias when determining the noise of the nitrocellulose membrane, the value of noise for strips was represented through the mean average of all pixels in the region of interest. The mean noise value was then subtracted from the test line intensity value to give a signal minus noise representation of test line signal per strip.