Lateral flow (LF) tests are frequently used for rapid delivery of qualitative diagnostic results. The detection sensitivity of these immunochromatography assays is largely dependent on the reporter technology. Many LF assays utilize reporters suitable for a visual interpretation of the test, implying less-sensitive detection than fluorescent reporter-based technologies that require LF strip readers to determine the test result. Here we describe the implementation of an unconventional and ultrasensitive fluorescent reporter technology: upconverting phosphor reporter particles. The reporter particles are excited with low energy 980 nm near infrared light and emit higher energy visible light that, similar to other fluorescent labels, allows a quantitative analysis of the test result. Detailed procedures regarding the LF strip production, bioconjugation of the reporter particles and the actual LF assay are described. The result of the UCP-LF assay is determined with dedicated readers and software, including a lightweight portable reader.