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 nonlinear luminescence response of UCNPs. As few as 2000 nanoparticles were detectable, and the linear dynamic range covered more than 5 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 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.

Central European Institute of Technology Masaryk University Brno 625 00 Czech Republic

Department of Biochemistry Biotechnology University of Turku 20520 Turku Finland

Department of Molecular Cell Biology Leiden University Medical Center 2300 RC Leiden The Netherlands

Institute of Analytical Chemistry Chemo und Biosensors University of Regensburg 93040 Regensburg Germany

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