(a) Schematic illustration of non-invasive tumor imaging based on multi parameter glucose metabolism and receptor-ligand engagement using dark quenched FRET acceptor. (b) Schematic illustration of Fluonanobody-based nanosensor via fluorescence resonance energy transfer for ultrasensitive detection of ochratoxin A. (c) Schematic diagram of high-performance fluorescent microspheres based on fluorescence resonance energy transfer mode for lateral flow immunoassay. (d) Schematic illustration of the Principle of the Ratiometric Fluorescence Aptasensor Based on Multivalent Aptamer Encoded DNA Flowers.