To help combat deadly outbreaks of Ebola, health care workers need a simple, portable test to determine immune response to the disease. Now, researchers have developed a color-changing, paper-based strip that detects antibodies against the virus in blood serum (ACS Nano 2018, DOI: 10.1021/acsnano.7b07021). Molly M. Stevens of Imperial College London and colleagues printed lines containing three antigens produced by different subtypes of the Ebola virus on one end of a commercially available paper test strip. To use the paper device, the team delivers a drop of blood serum to the other end of the strip and follows it with a solution of antibodies that label the target Ebola antibodies with gold nanoparticles. As the fluids wick past the test lines, Ebola antibodies in the serum bind to the nanoparticles and then to the antigens, causing the test lines to turn reddish purple within 15 minutes. A smartphone app measures the intensity of the line colors to give a positive or negative result. Compared with results from the gold standard lab-based assay, the test was 100% accurate at detecting individuals who had survived Ebola and gave one false positive with an uninfected sample.