This chapter provides an overview of state of the art in fluorescence detection using molecular-sized biosensors. In the past three decades, a number of activatable or tunable fluorescence biosensors have been developed, including FRET sensors, intercalating dyes, electron transfer-based sensors, fluorescein-based sensors, split GFP, biarsenical-tetracysteine sensors, aptamer sensors, H-dimer sensors, lanthanide-based sensors, carbon nanotube sensors, quencher transfer/detachment, FRET binary probes and chameleon NanoCluster Beacons. Researchers have proposed various methods to increase the dynamic range, the specificity, and the sensitivity of the aforementioned sensors. The requirements for using fluorescence sensors in biomedical imaging are reviewed, which provide general guidance for readers to conduct medical diagnosis with these newly-developed biosensing technologies. The chapter concludes with a brief perspective into the future of fluorescence-based biosensing systems.
Keywords: Activatable sensors, Fluorescence techniques, Nanomaterials sensors, Turn-on sensors, Tunable sensors.