Two-colour fluorescent imaging in organisms using self-assembled nano-systems of upconverting nanoparticles and molecular switches.

The water-insolubility of a potentially versatile photoresponsive 'turn-on' fluorescence probe was overcome by incorporating it into a nano-assembly containing an upconverting nanoparticle wrapped in an amphiphilic polymer. The appeal of the nano-system is not only in the ability to turn "on" and "off" the fluorescence from the organic chromophore using UV and visible light, it is in the fact that the nanoparticle acts as a static probe because it emits red and green light when excited by near infrared light, which is not effected by UV and visible light. This dual-functioning emission behaviour was demonstrated in live organisms.