An upconversion laser scanner has been optimized to exploit the advantages of photon-upconverting nanoparticles (UCNPs) for background-free imaging on a macroscopic scale. A collimated 980-nm laser beam afforded high local excitation densities to account for the non-linear luminescence response of UCNPs. As few as 2 000 nanoparticles were detectable and the linear dynamic range covered more than five orders of magnitude, which is essentially impossible by using conventional fluorescent dyes. UCNPs covered by a dye-doped silica shell were separated by agarose gel electrophoresis and scanned by a conventional fluorescence scanner as well as the upconversion scanner. Both optical labels could be detected independently. Finally, upconversion images of lateral flow (LF) test strips were recorded to facilitate the sensitive and quantitative detection of disease markers. A marker for the parasitic worm Schistosoma was used in this study.