L1CAM and Alzheimer disease: As illustrated in Figure 1B, this assay is comprised of two main steps: i) click chemistry‐mediated enrichment of two subpopulations of NEVs using Click MagBeads with one of the two TCO‐grafted antibodies targeting NEV markers, i.e., L1 cell adhesion molecule (L1CAM) and neural cell adhesion molecule (NCAM), and ii) assessment of β‐secretase activity of the enriched NEVs using β‐secretase FRET probes, providing a β‐secretase activity profile for each AD patient.