“…Second, different from the homogeneous CHA, 22 the target-initiated CHA reactions in this study are all enriched in the tiny space around micron-sized magnetic beads (MBs). Particularly, unlike the traditional bulk measurement by recording the fluorescence signal of the whole solution, 23,24 in this study, the minuscule sized MBs bearing enriched fluorophores are investigated as separate reaction units one-by-one through a flow cytometer (FCM), thus even very weak fluorescence signals can be detected. Third, an on-bead FRET readout mode is introduced to be monitored by versatile FCM.…”