Cells release extracellular vesicles (EV), which are present in all body fluids and regulate physiological processes. Moreover, because the properties of EV change during disease, EV are potential biomarkers for diseases as cancer, cardiovascular disease, and preeclampsia. Consequently, EV research is thriving as reflected by an exponentially growing number of publications and the 2013 Nobel Prize in Medicine. Nevertheless, an EV-based biomarker has still not been realized because existing technologies lack either sensitivity or speed. The technical challenge is to identify disease-specific EV between a multitude of other EV and non-EV particles with a diameter as small as 30 nm. To address this challenge, novel technology is urgently needed. In EV-Radar (RApid Detection And Recognition of EV), I will combine the sensitivity of dark-field microscopy with the speed of flow cytometry to achieve the first nanoparticle analyser capable of characterising single EV ≥30 nm at a clinically useful rate of 10,000 EV/s. The characterisation of 10,000 EV/s enables a significant count of disease-specific EV within minutes, which is a prerequisite to establish an EV-based biomarker. EV-Radar will consist of a disposable optofluidic chip and one camera to measure 1 scatter signal and 3 fluorescence signals per EV. To identify disease-specific EV, I will implement new analysis strategies based on combined fluorescence antibody detection, particle sizing, and refractive index determination. To demonstrate the clinical applicability of EV-Radar, I will identify tumour-derived EV in blood plasma of patients with prostate cancer. Once validated, EV-Radar will become the gold standard for single EV analysis in hospital laboratories. Outside the clinic, EV-Radar may become an important tool in microbiology (bacteria, viruses), materials science (synthetic nanoparticles), and oceanography (plankton, nanoplastics), as well as other fields where rapid identification of single nanoparticles is of critical importance.