Abstract: The invention relates to methods and devices for detecting the presence of a particle of interest (hereinafter an analyte particle) in a fluid. A detection device exemplary of the present invention filters a sample of the fluid to remove particles larger than the analyte particles. A reagent solution, containing reagent particles smaller than the analyte particles, is then added to the sample. The reagent particles will react with the analyte particles, if any are present, to form reagent-analyte complexes which are larger than the analyte particles. The sample is then filtered a second time to remove particles the same size as or smaller than the analyte particles. The sample is then tested for the presence of reagent-analyte complexes to detect the presence of the analyte particle in the fluid.